Properties of Speakers

[Buckle-meister]

Dear all

I've been thinking (I do that a lot :rolleyes: ) about speakers, their cabinets, drivers and crossovers, and have a few questions I'd like to put 'out there'. Im not looking to build my own speakers; I'm just curious about the parameters which lead folk to make speaker cabinets and drivers of the form that we commonly see.

1. I can understand why drivers are circular (as opposed to square etc. ;)), but why are they conical? Why not flat?

2. Since we don't see flat circular drivers, presumably the driver must be conical. This being the case, does the angle of slope of cone make a difference? If so, how do speaker/driver manufacturers decide what it should be? Most drivers for example are relatively shallow cones.

3. What about the central part of the driver? Excepting KEF's proprietory Uni-Q system of placing the tweeter in the centre of a midrange driver, is there a need for the central piece? Is it essentially a 'dust-cap'? If not, again, how does the speaker/driver manufacturer decide how big to make it? I would imagine for example that the larger the central piece was, the stiffer it would make the conical portion (good), albeit 'eating-up' a greater area of it (bad).

4. Whether there is or isn't a need for the central piece, how does the speaker/driver manufacturer decide on what form it should take? Monitor Audio drivers usually have an acute rocket-head-shaped central section, but many other manufacturers just have a flat disc. Is Monitor Audio's design purely for aesthetics?

5. Then there's the speaker cabinet/enclosure. Obviously when a driver moves it creates an opposite back-wave. In ported speaker designs, I believe that this is deliberately utilised to give the speaker, a small bookshelf for example, extra bass extension. Ideally though, I believe that ported designs aren't what one would want since although ports are 'tuned', the flow of air is still uncontrolled, hence the reason better speakers use 'passive radiators' which move in tandem with the actual drivers to try and negate the air-flow in, necessarily, a sealed cabinet enclosure. Is this true?

6. With room acoustics, a cube is the worst shape of room followed by a square-in-plan shape. So why are so many speaker cabinets made square-in-plan? Wouldn't the ideal speaker cabinet's dimensions all be dissimilar? If so, why don't we see more of this? Would it really be so difficult/expensive?

7. What about speaker cabinet edges/corners? Again, with room acoustics, all frequencies tend to find their way into the corners (hence the reason for placing bass-traps there), so why do we make the vast majority of speaker cabinets with straight edges and right-angled corners? Why not curved sides? Purely due to the expense of manufacturing?

8. What about speaker crossovers? Am I correct in saying that a normal crossover in a speaker consists of a small circuit board to divert frequencies from x to y up to the tweeter, and y to z down to the woofer etc etc? If so, what differentiates a typical crossover from a "Hard wired audiophile grade crossover" found in high-end speakers? Does the latter make a huge difference?

Well, that'll do me for the moment! :)

Regards

[Sheep]

I'll give someone these a whack.

1. There are flat drivers. But they are usually subwoofer drivers. I think they are conical for better sound dispersion.

2. I think the cones are at certain angle which works best to dispers the sound waves. If the agnle was sharper, the driver would be deeper.

3. The dust cap covers the voice coil, keeps dust of it, I guess. The size depends on the size of the voice coil.

4. I have only seen bullet phase plugs.

5. Next.

6. Probly expense.

7. Cost again...

8. Not touching that with a 40 foot poll. :rolleyes:

Sheep

[Buckle-meister]

I think the cones are at certain angle which works best to dispers the sound waves. If the agnle was sharper, the driver would be deeper.

So this implies that all drivers' conical sections are at the same angle. True?

The dust cap covers the voice coil, keeps dust of it, I guess. The size depends on the size of the voice coil.

I have only seen bullet phase plugs.

So the central portion does nothing at all? In that case, Monitor Audio's 'bullet'-shaped piece must just be for looks?

Not touching that with a 40 foot poll. :rolleyes:

Hehehe! Chicken! :)

Regards

[jaxvon]

1. It's about strength. Since the voice coil is located in the center of the driver, all of the force that moves the cone in and out comes from the center of the driver. If the driver was totally flat, then then it would flex like a drum head when you pushed on it and you would get distorted sound with all kinds of extra harmonics and such. Ideally, a flat surface would be great (as it has the greatest radiating area), but cannot be feasible due to the strength of the materials used. So a cone shape must be used. A cone has more rigidity in the direction the voice coil moves it and thus is less susceptable to flexing and distorting the sound (remember, the goal of a transducer is to create pistonic motion). The steeper the angle of the cone, the greater the rigidty, but the surface area that will actually push area is decreased. Some driver designers, like JL Audio (and others) use a W-Cone type design, where the voice coil is attched to a steep "W" shaped device wigh rigidity which is then affixed to a mostly flat inverted dome that actually interacts with the air to produce sound.

2.See #1.

3. The driver design you're talking about is called a "coaxial" driver. The two drivers share the same central axis about which they disperse sound. In one sense, this is a great design because it creates a nearly perfect "point source" type of sound production, where all of the sounds come from one point in space. However, because of the comprimises that must be made to affix the tweeter in such a position, the best sound is not always achieved ("Best Sound" being low distortion, etc, as well as a completely subjective though by me...Miklorsmith I know you love your Zu speakers).

The size of the hole in the middle of most speakers is dictated by the size of the voice coil. Most smaller drivers have a 1" to 1.5" voice coil, and thus the size of the dust cap is sized appropriately. Subwoofers often have a larger voice coil (3"+) to increase the power handlings as well as the strength of the voice coil. The size is also larger so all of the force is not concentrated in a very small area in the center of a 12" cone, but rather a more moderately sized area. Many designers often use inverted dust caps to utilize the maximum radiating area on the driver.

4. I'm not sure how driver designers decide on the dust cap/phase plug design. For reference a phase plug is the "rocket shaped" thing you're talking about. A phase plug (a true phase plug that is, not something that is an immitation and only looks pretty) is actually decoupled from the driver cone. This allows for air to enter the voice coil and cool the coils and magnets and increase power handling/endurance. The phase plug will also help guide the sound waves emited from the driver surrounding it.

5. Yes, many expensive speakers use a passive radiator/sealed enclosure design because the performance is more controlled. Of course, like you said, there are some drawbacks to the design, being bass extension, sound output (in dB), and efficiency.

6. I would think so, yes. And I don't know why more designers don't opt for this. I think it's more about cost.

7. Definitely about expese. B&W uses a design like this in their Model Nautilus speakers (beautiful, I must say), but then again, they cost around $80k/pr.

8. The components used in the crossovers are of varying quality. When you pay for a nicer speaker, the crossovers are made with parts of higher tolerances, and are often matched pairs so your speakers sound identical. High quality crossovers also utilize parts with higher power handling, or expensive, difficult to execute designs. Take Vandersteen for instance, their crossovers are all phase-correct/1st order designs. The benefit of this design means that the sound from all the drivers reaches your ears at the same time, all in phase. The bad part is that the rolloff is only 6dB per octave, which means drivers must be carefully selected because they have to operate outside of the normal range of their class (tweeters playing mids, etc).

[Sheep]

The phase plug is connected to the motor structure. It hepls disapate heat, and makes the cone lighter by not having a dust cap.

No, but the drivers may need a certain angle for strength, and sound. Even flat drivres still have a little indent on the back side.

[Buckle-meister]

It's about strength...If the driver was totally flat, then it would flex like a drum head when you pushed on it...

Ah yes, I should've thought of that.

B&W uses a design like this in their Model Nautilus speakers (beautiful, I must say)

I agree. Aren't they just stunning?

When you pay for a nicer speaker, the crossovers are made with parts of higher tolerances, and are often matched pairs so your speakers sound identical.

My speakers don't sound identical?

Take Vandersteen for instance, their crossovers are all phase-correct/1st order designs. The benefit of this design means that the sound from all the drivers reaches your ears at the same time, all in phase.

Is this the same as when I hear someone peak of 'time-aligned'? Wouldn't all drivers need to be time-aligned as a matter of course?

Also, it seems pretty daft to me that more manufacturers don't curve their cabinets. I mean, apart from looking better (opinion of course) and (surely) having a higher WAF, the additional cost to a, lets face it, mass produced speaker would be minimal I would have thought. Besides, even though it may be more expensive, folk would be prepared to spend more. The two negate each other.


Regards

[jaxvon]

My speakers don't sound identical?


Probably not if you measured them. I'm talking about super tight tolerances that are often more a matter of esoteric marketing.


Is this the same as when I hear someone peak of 'time-aligned'? Wouldn't all drivers need to be time-aligned as a matter of course?

Yes and yes. Dunlavy was another manufacturer that did this.


Also, it seems pretty daft to me that more manufacturers don't curve their cabinets. I mean, apart from looking better (opinion of course) and (surely) having a higher WAF, the additional cost to a, lets face it, mass produced speaker would be minimal I would have thought. Besides, even though it may be more expensive, folk would be prepared to spend more. The two negate each other.


Indeed. AV123 is the only manfacturer of "reasonably priced" speakers that I know of that offers curved cabinetry.

Some pictures!

Dunlavy:

http://www.soundstage.com/revequip/pics/dunlavy_sciva.jpg

Vandersteen:

http://vandersteen.com/images/mdl5big2.jpg

[Buckle-meister]

Yes and yes. Dunlavy was another manufacturer that did this.

You have me confused. You say that all drivers are time-aligned as a matter of course, yet you also say "Dunlavy also do this..." as if only few (high-end?) manufacturers do it. :confused:

AV123 is the only manfacturer of "reasonably priced" speakers that I know of that offers curved cabinetry.

Ah well, I guess it depends on one's definition of "reasonably priced"! :D

Some pictures!

I don't see anything out of the ordinary about the Dunlavys. :confused: I'd also tend to say that the Vandersteens were still angular rather than curved, albeit multi-faceted.

Regards

[MacManNM]

Good job Jax. This is a good thread. Well illustrated answers. Now, get to your homework!:p

[nibhaz]

Actually, all of the speakers in B&W's 800 range of speakers have curved cabinets. Whether or not these are considered affordable is a personal matter. Some snippets of B&W's speaker design philosophy can be found here (http://www.bwspeakers.com/bw800/). If you order the free DVD you'll find a wealth speaker design philosophy in lay terms, but of course you'll have to shift through some marketing BS.

[Buckle-meister]

Here's a few more for y'all:

1. Is the role of a passive radiator to negate the back-wave from the actual drivers, or simply to try and control the air movement within a speaker's cabinet?

2. As a passive radiator moves in conjunction with the actual driver to work on the air flow within a speaker's cabinet, isn't the passive radiator's back-wave, i.e what is coming out of the speaker, going to cause sound of it's own? It's a vibrating object after all. In other words, you're looking into the cabinet and trying to regulate the air flow inside, but forgetting about the air you are shifting behind you outside the cabinet!

3. What's the consensus on my previous question 8?: Would a "Hard wired audiophile grade crossover" found in high-end speakers make a huge difference to the speakers sound quality, or is the quality of loudspeakers mostly in the makeup of the drivers themselves?

4. Is rolloff a physical property of a driver? I thought the speaker designer decided on how smoothly or sharply the transferral from one driver to another (through use of the crossover) would be. Is this incorrect?

5. Are all drivers in all speakers 'time-aligned' as a matter of course, or is this something found only on more expensive speakers? If the latter, just how much of an improvement would this make?

Regards

[jaxvon]

Just for reference, it's spelled "ya'll". Keep in mind that "ya'll" is singular. The plural of "ya'll" is "all ya'll" :D

1. The purpose of a passive radiator is to utilize the negative movement [negative meaning in the direction towards the back of the speaker] of the main driver in producing sound. A port can also be used to do this, but problems arise with things like port noise. A passive radiator design will be able to produce higher SPL than a sealed enclosure or infinite baffle design with the same driver and amplifier, but still not to the same extent a vented enclosure can.

2. Yes, but that's the purpose! A passive radiator (for this example, positioned in line with the active driver but on the opposite side of the speaker cabinet) will create somewhat of a dipole effect, where it moves out from the cabinet when the other driver movies in, and vice versa. It is essentially an extension of the active driver. In a design like the BIC DV-84 speaker, with two active drivers and two passive radiators all placed on the front of the cabinet, the idea is to increase the SPL and bass response without porting the speaker. Keep in mind that a passive radiator design does attenuate bass response and decrease sensitivity, but not to the same degree that a totally sealed enclosure would.

On a side note, many people often prefer the sound of sealed enclosures or those with passive radiators because they feel the sound is subjectively "tighter", "punchier", and "more defined". I have nothing concrete to back up these statements, but I thought I'd throw them out there as food for thought.

3. Loudspeaker quality [in a traditional boxed enclosure with conical drivers] is divided between the cabinet design, driver design, and crossover design. Any of the three elements can greatly influence the sound, for better or for worse depending on the design.

Cabinets are generally designed to be inert as possible [this is of course dedicated by budget]. An inert design will stop the influences of resonance within the cabinet and thusly allow for lower distortion and more linear movement of the driver elements. Some designers, however (such as Sonus Faber and Boesendorfer) design speaker cabinets with real wood like one would design a musical instrument. Real wood, unlike MDF, has specific resonant properties that, when excited, will add harmonics to the sound that will often color it in a pleasing way [this indicates the presence of even-order harmonics].

A good driver design will have linear motion, fast transient response, and low distortion. No matter how high the quality of the other parts, a bad driver will yield "sloppy" [think Bose trying to do midbass and bass], distorted sound. When pushed with some higher power, the driver might bottom out, or start to resonate.

A proper crossover design is also integral in creating a quality loudspeaker with cohesive, low distortion sound. The crossover determines what frequencies are sent to which driver and can also alter the phase of the incoming electrical signals. An improperly designed crossover will result in poor driver integration and/or over-emphasis of certain frequencies. For instance, trying to send a 2kHz signal to a tweeter that is only flat down to 8kHz will yield bad results because it is being asked to reproduce a signal 2 octaves below its optimum operating range. The crossover controls this.

Using high quality components in a crossover is also important. When a passive crossover design is implemented (the kind one sees in almost every loudspeaker), the components must have a high-power handling to allow for uncompressed playback. The components must have a fine tolerance so the impedance doesn't vary too much and the function of the crossover doesn't change with use. The capacitors, inductors, resistors, and other devices used can determine the difference between a good design and a great design.

This does not mean that they need to use Vishray resistors, Black Gate capacitors, silver wire, and WBT silver solder with WBT terminations on the input board. If this is what you're getting at, then the idea that special "audio-grade" components are better is often BS. Vishray resistors are very high quality with tolerances, but this is why they work well in high-end designs. An example of this is the difference in the S/N ratio of 9dB or better when used in the RE Designs LPNA 150 monoblock.

4. The rolloff in speaker designs is determined by the crossover (as you rightly thought). However, a driver will have a frequency response, notated as one of the T/S parameters. This response dictates where the rolloff starts when a crossover is being designed. Take for instance the response chart for the Dayton 6" Reference Woofer (http://www.partexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=295-362):

http://www.partexpress.com/images/295-362m.jpg

http://www.partexpress.com/pdf/295-362g.pdf

5. No, this is a design choice that is often found in higher-priced speakers like Vandersteens, Dunlavys, Wilsons, and others. The design is a two part effort. First is the positioning of the drivers in the cabinet to allow for proper dispersion and in-phase radiation, and second, the crossover design. I know for a fact that Dunlavy and Vandersteen use a first-order crossover design that preserves electrical phase as it routes signals. Many people feel that this produces a very "complete" and "musical" sound. The downside is that a first-order crossover can only roll off frequencies at 6dB/octave, which means that the drivers used in such a design must have a wide usable bandwidth in order to accomodate signals that they do not usually encounter.


Keep the good questions coming, Robbie!

[Buckle-meister]

Just for reference, it's spelled "ya'll". Keep in mind that "ya'll" is singular. The plural of "ya'll" is "all ya'll" :D

Truly? I was under the impression that it was an abbreviation for "you all", hence "y'all".

...Robbie!

:mad: :mad: :mad:

BM or Buckle-meister please.

Regards

[malvado78]

This is one of the most informative threads I have ever read. I suggest it be Stickied somewhere. Maybe in the DIY. "Explainations of speakers designs"

Good job Jax. I would give you Chicklets all over the place but it won't let me because I've given yousome recently.

[j_garcia]

Buckle,

Most of what you are asking and more is answered in the Loudspeaker Design Cookbook Vol 6 in depth.

When you pay for a nicer speaker, the crossovers are made with parts of higher tolerances, and are often matched pairs so your speakers sound identical.

Drivers have tolerances too. The tweeters in my speakers come with their printed response curves and are selected to be as close to a matched pair as possible. The mids have good enough quality that they don't need to be matched. Crossover quality (components) does give you more driver control, but I wouldn't say it is going to make a huge difference in a well designed x-over once you reach a certain level of x-over component; meaning they should be of quality, but the most expensive components won't necessarily make a poor design or poor driver combination a good sounding speaker.

Time alignment can be done with the crossover as well, though companies that do a stepped baffle are also opting for a less complicated crossover, which is a good thing in my book. The spacing of the drivers, centerline to centerline is CRITICAL as well to minimize interactions at the crossover point(s).

Also, it seems pretty daft to me that more manufacturers don't curve their cabinets. I mean, apart from looking better (opinion of course) and (surely) having a higher WAF, the additional cost to a, lets face it, mass produced speaker would be minimal I would have thought.

The best shape, generally speaking, was found to be cylindrical with the driver perpendicular to the cylinder - very difficult to build. Guess what was second best? A FLAT, rectangular surface.

The phase plug is to break up reflections within the cone area. Sound leaves the cone surface and strikes the opposite side causing distortion - the closer to the center, the more it occurs. There are also parabolic curved drivers vs straight cone, though I don't know the implication of that on sound quality off hand.

A passive radiator does add to the overall output of the speaker. It keeps a sealed system, while allowing the primary driver to "think" it is in a larger enclosure.

YES, crossover plays a VERY key role in how good a speaker sounds, but exactly how is rather complicated.

My 902s use a 6dB/octave x-over, and they are quite musical. :)

[mulester7]

.....simply, a crossover chops, with rolloff of varying factors, the frequency signal sent to a specific speaker element, so the speaker element won't be required to attempt to reproduce extremes, and lose sound quality, or produce raspiness....with a three-way speaker enclosure, an internal three-way crossover chops the signal to the midrange element on both ends, high and low, with the top of the woofer being chopped, and the bottom of the tweeter being chopped.....



Crossover

The crossover splits up the frequency spectrum into pieces, which are then handed over to various speaker drivers. A crossover is necessary in a speaker because one driver cannot efficiently handle all sound reproduction tasks across the entire audible spectrum (the sounds distinguishable by the human ear – from around 20 Hz to 20 kHz).

A two-way crossover, for instance, may split the frequency spectrum into a frequency band from 20 Hz to 2 kHz and from 2kHz to 20 kHz. The woofer section of the speaker would then reproduce the section from 20 Hz to 2 kHz while the tweeter took over above 2 kHz. This scenario works essentially the same for all crossovers, however, there are two specific types of crossovers – active and passive.

Active crossovers are adjustable and require power (normally an AC power source from a wall outlet) to operate while passive crossovers are not adjustable (by the user, the factory can set the crossover but cannot change the setting without changing the crossover) and do not require power to operate.

http://www.audiovideo101.com/dictionary/dictionary.asp?dictionaryid=117&term=Crossover

[Buckle-meister]

...there are two specific types of crossovers – active and passive.

What are the advantages and disadvantages of each?

Regards

[j_garcia]

They do the same thing, except one is powered and the other is not. The active x-over is variable for each crossover point as well, and may offer a number of parameters to tailor the x-over to the particular design and drivers.

[mulester7]

What are the advantages and disadvantages of each?

Regards.....Buckle, I don't think there's an advantage or disadvantage to either, but simply a matter of what is required....with an active crossover, like a Paradigm X-30, a Behringer 2496, or the crossover in a powered sub, AC is required, but then again, I'm not for sure the crossover in a sub requires AC in any way, and the AC to a sub is probably only to power the amp section, I don't know for sure as I've never had a powered sub....the crossover in a speaker enclosure is considered passive, as it requires no AC and accepts wattage in an inductance form, and yes, you can put both ends of the speaker wire to a speaker in your mouth and turn up the gain and continue to smile, feeling nothing....other comments, please....Gene?.....

[mulester7]

The active x-over is variable for each crossover point as well, and may offer a number of parameters to tailor the x-over to the particular design and drivers......excellent.....

[j_garcia]

For a sub, the adjustments are a little different than an active x-over for other drivers. Subs generally use a passive x-over, but with the ability to adjust parameters of the x-over to suit a room. The bottom octave tends to have the most issues with room interactions, so the phase (preferably variable, not just 0 deg or 180 deg) and x-over point (dial in your blend as needed) controls can be a valuable tool to "tweak" the sound for a given setup.


5. ....Ideally though, I believe that ported designs aren't what one would want since although ports are 'tuned', the flow of air is still uncontrolled, hence the reason better speakers use 'passive radiators' which move in tandem with the actual drivers to try and negate the air-flow in, necessarily, a sealed cabinet enclosure. Is this true?

Properly designed ported speakers can sound very good. There are a variety of ways to vent a cabinet besides a port, but the resulting goal, sealed or vented, is the same - clean, linear response. There is such a thing as an ideal port design as well, which avoids turbulence generated as the air escapes the enclosure.

6. With room acoustics, a cube is the worst shape of room followed by a square-in-plan shape. So why are so many speaker cabinets made square-in-plan? Wouldn't the ideal speaker cabinet's dimensions all be dissimilar? If so, why don't we see more of this? Would it really be so difficult/expensive?

I'm not sure I understand this question? Are you talking about room shape or physical speaker shape? You did hit on a key point though, baffle size and shape (not including corners, see below) is quite important.

7. What about speaker cabinet edges/corners? Again, with room acoustics, all frequencies tend to find their way into the corners (hence the reason for placing bass-traps there), so why do we make the vast majority of speaker cabinets with straight edges and right-angled corners? Why not curved sides? Purely due to the expense of manufacturing?

Because it really doesn't make that much difference. It's pretty much entirely aesthetic. In the LDC vol6, there's info on a study done on baffle size showing that in order for chamfered corners to be effective, their size would need to be roughly equal to the size of the front baffle, making the speakers quite large in profile and offering little real benefit compared to the added size and cost of construction.

These (http://www.josephaudio.com/product.rm7sisigmk2.html) guys have a straight forward, rather plain looking cabinet design (aside from the beautiful birdseye maple shown) and they sound simply amazing... Read up on their x-over (120dB/octave!!), it's a very interesting type I had not seen before hearing these speakers, and let me tell you, it WORKS.

[Buckle-meister]

I'm not sure I understand this question? Are you talking about room shape or physical speaker shape? You did hit on a key point though, baffle size and shape is quite important.

Firstly, is the baffle the same as the front-face, i.e. the face the drivers are (usually) attached to?

As to your question; the speaker cabinet's shape.

If a square is such a bad geometric shape acoustically speaking, why are so many speaker cabinets made square (in plan)? I would have thought that, as for rooms, a speaker cabinet of dissimilar dimensions would be better.

Regards

[j_garcia]

Yes, baffle is what would be considered the front face that the drivers are attached to. The baffle width does play a role in a vertically oriented speaker.

Semi-related, here's another one to ponder: flush tweeters? :) Edge diffraction is one reason why the front baffle of the speaker is a factor; moreso for higher frequencies.

[Buckle-meister]

The baffle width does play a role in a vertically oriented speaker.

In what respect? Is a narrow or wide baffle preferred? No, don't tell me; it's not that simple! ;)

Regards

[j_garcia]

No, I don't think it's that simple, though I would say that is likely a fairly true statement. Too wide of a baffle will affect the sound due to edge diffraction - the sound waves are affected by the front baffle's surface, so the wider it is relative to the driver size, the greater that interaction is. How one goes about figuring out what is optimum for a given driver, I don't know.

Check out the driver spacing on my speakers. Notice how the mids overlap the tweeter slightly. This was done, I'm guessing, to get the proper centerline to centerline spacing of the drivers to minimize the interaction of the drivers. Also note the width of the cabinet compared to the driver size. Cabinet volume is achieved by depth:
http://www.gr-research.com/images/maplepair.jpg

(those aren't mine, these (http://www.gr-research.com/images/brians.jpg) are my actual mains).

[jaxvon]

These (http://www.josephaudio.com/product.rm7sisigmk2.html) guys have a straight forward, rather plain looking cabinet design (aside from the beautiful birdseye maple shown) and they sound simply amazing... Read up on their x-over (120dB/octave!!), it's a very interesting type I had not seen before hearing these speakers, and let me tell you, it WORKS.

Wow, that speaker design looks VERY similar to a design suggested by Seas, the driver manufacturer.

http://www.seas.no/trym.htm

Edit: obviously the crossover topology is different.

[j_garcia]

Wow, that speaker design looks VERY similar to a design suggested by Seas, the driver manufacturer.

http://www.seas.no/trym.htm

Edit: obviously the crossover topology is different.

Yep. I know a guy who built a kit based on the same drivers using a "normal" passive x-over (may be that actual design) and he says it still sounded pretty amazing. Those drivers are pretty nice stuff :)

[Buckle-meister]

Just.....can't.....stop...................thinking ....:eek:

1. In a multi-driver cabinet, is the cabinet internally split into distinct chambers that are completely sealed off from one another, or can the air circulate within the entire cabinet? Are chambers ever mostly but not completely isolated from other chambers? Might one driver have it's own chamber, but two others share one combined chamber?

2. Passive radiators are also known as ABR-loaded (Auxiliary Bass Radiator). Ports are also known as 'Reflex-loaded'. What exactly does 'Reflex' mean?

3. What exactly does a 'two-way' or 'three-way' design mean? Is it the number of crossover points that there are? I ask because although my own are 'three-way', I have five drivers in addition to the tweeter. The specification refers to the drivers as 1-bass and 4-mid. Would I therefore be correct in saying that the three crossover points for my speakers will be for the tweeter, (all) the mids, and the bass?

4. I know that 'porting' a cabinet reinforces the speakers bass, but how? My front towers have three ports (three-way?, three chambers?). When the music is at moderate volume, if I place my hand at the mouth of the port I can actually feel the air coming out of them. How is air coming out of the back of a speaker making me hear greater bass?

Regards

[j_garcia]

WOW, what's driving this thirst for knowledge? I've been curious about what goes into making a speaker sound good for years too, so I started buying books. It hurt my head at first, but after a lot of reading, it finally started to make a little bit of sense to my over taxed brain. There still seems to be a bit of voodoo if you ask me.

1. In a multi-driver cabinet, is the cabinet internally split into distinct chambers that are completely sealed off from one another, or can the air circulate within the entire cabinet? Are chambers ever mostly but not completely isolated from other chambers? Might one driver have it's own chamber, but two others share one combined chamber?

Depends (no not the diapers, deal with that yourself). They can be, but they don't have to be usually. Some manufacturers do completely isolate the mid and tweeter from the air volume for the bass drivers.

2. Passive radiators are also known as ABR-loaded (Auxiliary Bass Radiator). Ports are also known as 'Reflex-loaded'. What exactly does 'Reflex' mean?

Have to get back to you on that one.

3. What exactly does a 'two-way' or 'three-way' design mean? Is it the number of crossover points that there are? I ask because although my own are 'three-way', I have five drivers in addition to the tweeter. The specification refers to the drivers as 1-bass and 4-mid. Would I therefore be correct in saying that the three crossover points for my speakers will be for the tweeter, (all) the mids, and the bass?

Yes. X-over points, not the number of drivers.

4. I know that 'porting' a cabinet reinforces the speakers bass, but how? My front towers have three ports (three-way?, three chambers?). When the music is at moderate volume, if I place my hand at the mouth of the port I can actually feel the air coming out of them. How is air coming out of the back of a speaker making me hear greater bass?

The port is accentuating a particular frequency, the tuning point of the cabinet, which is based on the cabinet volume, the driver's specs, and the designer's intent. You have three ports because the tuning frequency desired would create a port that was too long to fit in the cabinet, so they used multiple ports to achive the tuning.

[j_garcia]

So when will we see your design? Buckle-Meister's Signature Series speakers? :D

Check these out too. Very cool cabinets: TIK (http://www.jbl.com/home/products/series.aspx?SerId=TIK).

[jaxvon]

Just.....can't.....stop...................thinking ....

1. Depends on the manufacturer. With cheaper speakers, there is generally nothing in the way of isolation. As you spend more money, manufacturers start doing this with their cabinets. The ultimate in terms of isolation would be a design like the B&W Model Nautilus, where every driver has its own chamber.

2. Reflex I guess is somewhat of a misleading term, as there is no "flexing" going on. It's just a term to denote the movement of the air out of the port in reaction to the movement of the driver.

3. You got it. An n-way design uses n crossover points in its crossover topology. You would be somewhat correct. A "crossover point" refers to the specific frequency where the crossover is centered. But you are right in the sense that the three groups in your 3-way speaker are the tweeter, the mids, and the bass.

4. Porting a speaker allows the backwave of the driver to escape the cabinet, which increases sound output. Because the back pressure of the driver is also reduced, it can move more easily which translates to higher efficiency.

The fact that your speakers have three ports is just the design, there is no special name for it.

The air you feel coming out the back of the speaker is the air being pushed by the driver when it is in negative motion [wherin "positive motion" is defined as excursion in the direction away from the cabinet and "negative motion" is defined as the direction into the speaker cabinet]. When a speaker cone moves outward in the positive direction, it compresses the air molecules in front of it. This is called a "compression". The point where it is fully exterted and creating the highest amount of pressure is the peak of the sound wave [for simplicity we're discussing a pure sine wave]. The driver then moves in the negative direction. It keeps going past its equilibrium point [the equilibrium point is the place where the driver will come to rest when no forces are acting on it] to a negative excursion determined by the amplitude of the incident electrical signal. At this point, the driver has created a low-pressure area in the air in front of it. This low-pressure area is called a rarefaction. These two points, the compression and rarefaction, translate to the peaks and valleys on a two dimensional graph of a sine wave. So how does this affect your speaker? Well, you normally are only creating sound from the compressions and rarefactions produced by the front of the driver. When you add a port, a passive radiator, or in the case of the Linkwitz Orion remove the cabinet entirely, you gain the use of the compressions and rarefactions created by the back of the driver cone. This means you have effective two sources of sound waves, operating 180 degrees (or pi radians for you purist types) out of phase. This is the dipole effect. Now, your speakers are not true dipoles because they do not have exposed drivers to the rear. However, the utilization of the backwave is along the same lines as a dipole speaker (like the Orion, Martin Logan designs, or Magnepans).

Note: Bi-pole is not to be confused with Di-pole. A bi-polar speaker has two radiating elements that operate in-phase, meaning that when one exterts outward, the other does the same thing. A di-polar speaker operates 180 degrees out of phase, meaning that when one driver moves out, the other moves in.

And of course, a port on the back of your speaker will increase your bass because it will interact with the room (perhaps a wall) near your speakers and, if they're near a wall or in a corner, you will experience a room-gain.

Edit: Derr...forgot about th port tuning. Thanks Mr. Garcia.

[Buckle-meister]

WOW, what's driving this thirst for knowledge?

Understanding is happiness.

I've been curious about what goes into making a speaker sound good for years too, so I started buying books.

Why buy books when I have you?! You're the best J Garcia!!! :eek:

The port is accentuating a particular frequency, the tuning point of the cabinet, which is based on the cabinet volume, the driver's specs, and the designer's intent.

What? One frequency? Do you mean a range of frequencies centred around a particular frequency?

You have three ports because the tuning frequency desired would create a port that was too long to fit in the cabinet, so they used multiple ports to achive the tuning.

Indeed. I just read another post in an adjacent thread. I had no idea ports (http://www.krellonline.com/html/m_LAT_p_LAT1b_ALL.html) (thank you Jaxvon) were so long!

[Buckle-meister]

Out of curiosity (another question might be in the pipeline!), what would a typical crossover frequency to a tweeter be?

Regards

[jaxvon]

There is no typical one, it depends on the driver. B&W uses a 4kHz crossover on their 705 bookshelves, but another manufacturer like Paradigm crosses over their Monitor line of speakers at 2kHz.

[j_garcia]

What? One frequency? Do you mean a range of frequencies centred around a particular frequency?

Yes, that would be more correct, but I would suspect the range is pretty narrow, centered around that frequency.

Bass reflex:
The bass-reflex enclosure makes use of a tuned port which projects some of the sound energy from the back of the loudspeaker, energy which is lost in a sealed enclosure. But care must be taken to avoid the back-to-front cancelation of low frequencies which characterizes unenclosed loudspeakers. This is avoided by tuning the cavity resonant frequency of the enclosure to the free-cone resonant frequency of the loudspeaker. This has the effect of projecting bass frequencies from the port in phase with the sound from the front of the cone, at least at the resonant frequency. The overall effect is the increasing of bass efficiency and the extension of the bass response to lower frequencies.

"Normal" tweeters? It's hard to define. Some may start around 1500Hz, others may roll off at 3000Hz and need to be blended higher than that. It is application dependent and will depend mostly on the driver that it needs to be blended with and how smooth of a transition you're looking for. In the typical 2-way, it will likely be lower than it would in a 3-way speaker for example, because the tweeter can be crossed higher due to the fact that the midrange driver is likely covering a higher range as well; handing off only the lowest extension of the speaker as a whole to the bass driver.

[Buckle-meister]

There is no typical one, it depends on the driver. B&W uses a 4kHz crossover on their 705 bookshelves, but another manufacturer like Paradigm crosses over their Monitor line of speakers at 2kHz.

That's ok, it will serve for my purposes (it's just what I thought).

Whilst the human ear is typically taken to hear from 20Hz to 20kHz, I understand that very few instruments play frequencies at either end of the spectrum. I read recently that the major part of music reproduction falls within 12kHz. This being true, and given that a typical tweeter is crossed-over at somewhere around 2 to 4kHz:

Wouldn't this mean that the tweeter was undisputedly the most important driver in any speaker because of the greater proportion of frequency range that it must reproduce compared to the other drivers?

Regards

[Buckle-meister]

In the typical 2-way, [the tweeter]...will likely be [crossed-over]...lower than it would in a 3-way speaker for example, because the tweeter can be crossed higher due to the fact that the midrange driver is likely covering a higher range as well; handing off only the lowest extension of the speaker as a whole to the bass driver.

Why wouldn't one always shoot for a tweeter crossed over as low as possible? I mean, given that the other drivers are more massive, which I understand impacts on transient response (how dynamic/quickly the driver can be made to move back and forward I believe?), and the fact that with a larger surface area, almost by inspection, the other drivers will distort more than a tweeter, why not punt more audible information to a nice small, extremely accurately vibrating membrane? :)

Regards

[jaxvon]

That's ok, it will serve for my purposes (it's just what I thought).

Whilst the human ear is typically taken to hear from 20Hz to 20kHz, I understand that very few instruments play frequencies at either end of the spectrum. I read recently that the major part of music reproduction falls within 12kHz. This being true, and given that a typical tweeter is crossed-over at somewhere around 2 to 4kHz:

Wouldn't this mean that the tweeter was undisputedly the most important driver in any speaker because of the greater proportion of frequency range that it must reproduce compared to the other drivers?

Regards

Ah, but it does not! Remember that music is based around octaves. One octave is a doubling of the frequency. Take the standard tuning note of A440 (440Hz). One octave up from that is 880Hz. So if you crossover at 4kHz on a tweeter, it's only covering around 3 octaves. The midrange is actually the most important driver, as that is where the majority of the sound in music is.

The reason tweeters don't cover more of a range is because of the physical properties of the driver. They simply can't reproduce frequencies below a certain point in the same way a midrange can't produce frequencies at an audible level or with low distortion above a certian level. Also, lower frequencies require much more extension of the driver in order to produce sound at the correct level.

[j_garcia]

I read recently that the major part of music reproduction falls within 12kHz.

Where'd you read that? I'd be curious to read what else it said. People hear differently, and some are either sensitive to certain freuquencies that others may not be sensitive to or may not hear at all. The vocal range is roughly 300-3000 and IMO, that's what I'm generally listening for when I audition a speaker - the midrange and how clear it is. That was a big factor in my choosing the speakers I own. The highs have an influence too though, as they do play quite a bit of content, a surprising amount actually in some cases. Ever taken a bi-wirable speaker and disconnected one of the terminals? It's interesting when you hear just what each of the drivers is playing.

[Buckeyefan 1]

If anyone's experimented with the graphic eq on the Denon 3805, they'd soon realize the frequencies that have the greatest effect on sound are the 250Hz through 2kHz.

63Hz, 125Hz, 4kHz, and 8kHz don't affect the sound nearly as much as those between 250-2000Hz. Denon doesn't even bother putting anything under 63Hz, nor above 8000Hz because so little occurs outside of these frequencies. Many pro-audio eq's rarely go outside the 31.5Hz to 16,000Hz range.

[Buckle-meister]

I read recently that the major part of music reproduction falls within 12kHz.

Where'd you read that?

'Twas here (http://www.audioholics.com/techtips/roomacoustics/Acoustics101THX.php) ;) The following quote has been taken from it:

Most audiophiles believe “the goal” of a high performance home theater set-up is to achieve 20Hz – 20KHz bandwidth. That’s easier said than done. But what if that lofty 20Hz to 20KHz capability isn’t really all that necessary 99% of the time? John stated that “everyday sounds” usually fall between 40Hz and 12,000Hz. He’s correct. 40 hertz is open fret on the E-string of a bass guitar. Twelve thousand hertz is roughly the third harmonic of the highest fundamental frequency on a piano which is C7 at 4186Hz. Get beyond the third harmonic to the fourth at 16,000Hz + and the level of that harmonic is now around -20dB below the 4186Hz primary frequency.

This is why, once frequencies start getting over 12KHz, reviewers start describing the sound with terms like “air around the instruments”. To be sure, the difference can be heard. But it is very, very subtle and requires a listening environment with an extremely low noise floor.

Regards

[Buckle-meister]

The midrange is actually the most important driver, as that is where the majority of the sound in music is.

I guess this explains why four of my front tower's five bass drivers are dedicated to the midrange. :cool:

Ever taken a bi-wirable speaker and disconnected one of the terminals? It's interesting when you hear just what each of the drivers is playing.

Yes! It is! I have my towers biwired (I know, I know ;)), but the amp-end of the cables are plugged into the Speaker A and Speaker B terminals which, via a little button behind the front panel of the amp, I may select which to listen to (normally both A and B are required to be selected). It is interesting.

Further questions:

1. If, as seems to be the case, my three-way speakers are crossed over for the (single) woofer, the (four) midrange drivers and the tweeter, would I be correct in saying that for a given SPL, the four midrange drivers (all acting simultaneously) will have an excursion (i.e. physical movement backwards and forwards) one quarter of say the bass driver reproducing the same tone at the same SPL (even though in principle the bass driver wouldn't be sent the same information, what with the crossover directing a different range of frequencies to it)?

2. If 1 above is correct, does it automatically follow that that is a good thing, since the less each driver moves, the more accurately it will reproduce sound?

3. I understanding that speakers are tested in anechoic chambers with a microphone spaced 1m away from the 'baffle' ;) whilst being fed 1 Watt of power giving rise to the common specification x-dB/W/m. But how do they test a multi-driver speaker? Is the mic lined up with the centre of the tweeter?, the midrange? the woofer? Are separate tests done for each driver, or is the mic placed in one 'average' position for the entire speaker?

Regards

[jaxvon]

1. I don't think there is a linear relationship here as you're implying, but I don't honestly know what the function would look like.

2. Yes. Driver distortion is lower when the cone moves less. As cool as it is to watch a subwoofer move like 3" in its excursion, it will produce better sound when it isn't being driven towards the edges of its performance envelope. The same goes for any driver.

3. I believe the standard practice is to line up the microphone with the tweeter. Many manufacturers also provide measurements 15, 30, and 60 degrees off axis in the horizontal plane.

[MacManNM]

#3. Sometimes they move back 2 or 4 meters make the measurement and calculate the rating at 1M.

[Buckle-meister]

Another few for you:

1. Why, if the midrange is the most important part of a speaker, is it recommended that the tweeter ideally be at ear height?

2. Why are we interested in the off-axis response of a speaker in an anechoic chamber? I could guess that it is because most folk have their front mains speakers pointing slightly behind them, i.e. off-axis, but I've got a feeling that that's not it at all.

3. Why, no matter how loud I have the volume, do I not feel a shock if I touch the terminals at the back of the speaker? I was under the impression that a reasonable amount of current was required to drive speakers?

Regards

[jaxvon]

1. The upper frequencies of the audio spectrum reproduced by the tweeter are the most directional. Also, tweeters tend to lose their flat response when you move off axis, much moreso than midrange and bass drivers.

2. That's partially it. Research at the NRC has also proven that good off-axis response is one of the main ingredients in a good-sounding speaker. Good off-axis response also ensures a wider "sweet spot". This might not be a problem with your speakers, but if you've ever experienced a speaker with poor off axis response, it can be somewhat of a pain to listen. Magnepans are a good example. When you're in the sweet spot, the soundstage and everything is amazing. But move your head too much and there is an audible decline in the overall quality of the sound.

3. Why on EARTH were you doing this? Regardless, there is often not that much power going into your speakers. Even at really loud levels, you might be pushing 50w into them. In addition, to really feel like you're being electrocuted, you need a decent amount of voltage. I doubt that your amp is putting out that kind of voltage.


Addendum: Regarding question #1 from post #1 on page #1, there is one company I know of that makes flat drivers. That would be Phase Tech. But unlike most drivers, their flat faced drivers are made of solid, low density material. Read up on them here:

http://phasetech.com/cgi-bin/index.cgi?page=12 It's all interesting, but the pertinent info is under the links "Solid Piston Driver" and "Why RPF?"

[Buckle-meister]

Thank you Jaxvon. ;)

The upper frequencies of the audio spectrum reproduced by the tweeter are the most directional. Also, tweeters tend to lose their flat response when you move off axis, much moreso than midrange and bass drivers.

Ah yes, I had forgotten that higher frequencies are more directional. However, take a look towards the bottom of this (http://forums.audioholics.com/forums/showpost.php?p=93295&postcount=6). As WmAx states, the air is causing higher frequencies to deviate from flat anyway. I got the impression from the link that a flat response for the high frequencies would sound far too 'bright' for, more than likely, the majority of people.

Why on EARTH were you doing this?

To test my theory. :) It's not like I stuck my tongue to it or anything.

...to really feel like you're being electrocuted, you need...

Oh jeez. :eek: :D

Regards

[chikoo]

Dear all


1. I can understand why drivers are circular (as opposed to square etc. ;)), but why are they conical? Why not flat?


Regards

Conical shape allows the speaker to produce all ranges of sound.
Low frequency sounds are produced at the outer edges of the driver and hence most subwoofers are more effective as they grow in diameter since they have more area on the periphery to move the air.
The smaller the cone diameter, the better it will reproduce the higher frequency.

In fact as a kid growing up I have used with great satisfaction dual cone Philips speakers, which basically makes a tweeter in the full range speaker by attaching a small cone in the middle on top of the dust cap.
see the picture for better visualization:

http://store1.yimg.com/I/yhst-3248687470797_1873_287019

[Buckle-meister]

I've thought of another question, but first...

Conical shape allows the speaker to produce all ranges of sound. Low frequency sounds are produced at the outer edges of the driver and hence most subwoofers are more effective as they grow in diameter since they have more area on the periphery to move the air.

I understood that bass drivers had to be fairly large to effectively move the air for the long wavelengths of bass, but I didn't know that 'bass was produced at the outer edges of the driver'. Is this definitely correct? :confused:

As for my own question to put 'out there':

Say we have a speaker with a tweeter, midrange driver and passive radiator. As I understand things, the passive radiator is not actually powered, but instead relies upon the pressure in the speaker cabinet caused by the midrange driver to drive it.

The thing is, if that is true, then doesn't that mean that the midrange driver and passive radiator are 180 degrees out of phase with each other? I mean, when the midrange driver moves into the cabinet, it must cause high pressure which would then cause the passive radiator to move out from the cabinet and vice versa; i.e. out of phase! :)

Regards

[WmAx]

I understood that bass drivers had to be fairly large to effectively move the air for the long wavelengths of bass, but I didn't know that 'bass was produced at the outer edges of the driver'. Is this definitely correct? :confused:

That is not correct. The poster to which you are responding to is in error.



The thing is, if that is true, then doesn't that mean that the midrange driver and passive radiator are 180 degrees out of phase with each other? I mean, when the midrange driver moves into the cabinet, it must cause high pressure which would then cause the passive radiator to move out from the cabinet and vice versa; i.e. out of phase! :)

No. The air coupled link and mass equivalent of the passive radiator acts as a spring and is bound by the physical laws therein. The two will move in contradictory (as a solid coupled connection) only under the resonant frequency of the spring system. As you approach the resonant/tuning frequency, they move in phase together.

-Chris

[Buckle-meister]

Would you mind clarifying this a bit if you don't mind?

The air coupled link and mass equivalent of the passive radiator acts as a spring and is bound by the physical laws therein.

I read this as 'everything must obey the laws of physics' True? If so, I agree. ;)

The two will move in contradictory (as a solid coupled connection) only under the resonant frequency of the spring system.

This is where I'm a little confused. I read this as '(if the two acted as though rigidly connected to one another) the two will move out of phase only when they vibrate at the resonant frequency of the system (that is the drivers/air etc)'. The thing is, if that is true, then...

As you approach the resonant/tuning frequency, they move in phase together.

...this wouldn't make sense as it would contradict the previous statement.

Please help me understand.

[WmAx]

This is where I'm a little confused. I read this as '(if the two acted as though rigidly connected to one another) the two will move out of phase only when they vibrate at the resonant frequency of the system (that is the drivers/air etc)'. The thing is, if that is true, then...

I mean that below the resonant frequency of the passive radiator tuning frequency, the air inside of the enclosure is stiff enough to move the passive radiator through volume displacement. At these low frequencies, when the speaker moves out, the radiator moves in, thus the two are producing sound pressure that is contradictory(out of phase). As you approach the resonant frequency, the two begin to move in phase(the radiator moves outward when the speaker moves outward) because the air volume begins to act as a spring. If you have ever held a spring at one end, with a weight attached to the other end, you realize that if you move it up and down very slowly, it will move together with the motions of your hand. However, if you speed up the motion, the spring will begin to move in an opposite/inverse direction from your hand motion. In addition, the movement of the speaker cone is drasticly reduced around the tuning frequency of the passive radiator, because the passive radiator is operating around and at it's resonant frequency. Imagine that same spring with weight attached experiment, where a very small hand motion incites a much larger movement of the spring in the inverse direction. BTW, a ported enclosure operates on the same principles(you just replace mass loaded drone cone with a mass of air in a port).

-Chris

[Buckle-meister]

Thanks very much WmAx.

I mean that below the resonant frequency of the passive radiator tuning frequency, the air inside of the enclosure is stiff enough to move the passive radiator through volume displacement. At these low frequencies, when the speaker moves out, the radiator moves in, thus the two are producing sound pressure that is contradictory(out of phase). As you approach the resonant frequency, the two begin to move in phase(the radiator moves outward when the speaker moves outward) because the air volume begins to act as a spring.

Does that mean that in a similar way to an actual powered driver, a passive radiator is only effective from its tuning frequency and above?

If you have ever held a spring at one end, with a weight attached to the other end, you realize that if you move it up and down very slowly, it will move together with the motions of your hand. However, if you speed up the motion, the spring will begin to move in an opposite/inverse direction from your hand motion. In addition, the movement of the speaker cone is drasticly reduced around the tuning frequency of the passive radiator, because the passive radiator is operating around and at it's resonant frequency. Imagine that same spring with weight attached experiment, where a very small hand motion incites a much larger movement of the spring in the inverse direction.

The spring example is an excellent analogy. Does the drastic reduction of the powered driver's motion at the passive radiators resonant frequency not simply result in a transferral of (it sounds like) excessive excursion from one driver (powered) to another (passive) though? If so, how is this a good thing?

...a ported enclosure operates on the same principles(you just replace mass loaded drone cone with a mass of air in a port).

Isn't this similar to how a Helmholtz resonator works?

[WmAx]

Does that mean that in a similar way to an actual powered driver, a passive radiator is only effective from its tuning frequency and above?

The passive radiator or port is effective at and around the tuning frequency. It reduces in efficiency/output rapidly as you rise above or below this resonant frequency.

The spring example is an excellent analogy. Does the drastic reduction of the powered driver's motion at the passive radiators resonant frequency not simply result in a transferral of (it sounds like) excessive excursion from one driver (powered) to another (passive) though? If so, how is this a good thing?

This is a good thing in terms of energy efficiency at the lower frequencies. This is a good thing in terms of reducing speaker motor non-linear distortion, because the motor gets to operate within a much narrower portion of the magnetic gap and within a much narrower region of the mechanical movement of the speaker(speaker suspensions are not perfectly linear, nor are the motors, and these properties become worse as the excursion is increased).

A ported box has two tunings. One is the tuning of the box volume, which dictates the low frequency response before the passive radiator/port output contributes to output. The 2nd tuning is the actual passive radiator/port tuning. These two distinct tunings can be seen easily in impedance measurements.

[/quote]Isn't this similar to how a Helmholtz resonator works?[/QUOTE]

Yes, exactly.

-Chris

[Buckle-meister]

The passive radiator or port is effective at and around the tuning frequency. It reduces in efficiency/output rapidly as you rise above or below this resonant frequency.

It almost sounds from the above that passive radiators, and indeed ports contribute very little. This would seem to agree with Helmholtz resonators where a very specific and I gather, relatively narrow band of frequencies is acted upon.

A ported box has two tunings. One is the tuning of the box volume and speaker resonance, which dictates the low frequency response before the passive radiator/port output contributes to output. The 2nd tuning is the actual passive radiator/port tuning. These two distinct tunings can be seen easily in impedance measurements.

If my first comment has any truth in it, does the above quote imply that a port or passive radiator's main contribution is in SPL rather than bass extension lower than that obtainable from the drivers and cabinet alone?

[WmAx]

It almost sounds from the above that passive radiators, and indeed ports contribute very little. This would seem to agree with Helmholtz resonators where a very specific and I gather, relatively narrow band of frequencies is acted upon.

Let's examine the average response of the same driver( that has an EPB equally suited to sealed or ported enclosure ) in both situations:

http://www.linaeum.com/images/ebp_equal.gif

F3=55Hz in sealed alignment.

F3=36Hz in ported alignment.

If my first comment has any truth in it, does the above quote imply that a port or passive radiator's main contribution is in SPL rather than bass extension lower than that obtainable from the drivers and cabinet alone?

Depends on what you mean by bass extension. Becuase the passive radiator/ported system is a 4th order alignment, it will average 24db/ octave attenuation rate. A sealed system is a 2nd order alignment, thus averaged attenuation rate is 12db/octave. Ultimately the sealed system will have greater extension, but only at frequencies that are far below the *0dB reference level that is considered flat. Note the response of the sealed vs. ported example in my illustration. I did not extend the dB scale low enough for you to see, but looking at the slope angles, you can see that the ported output will eventually not be as great as the sealed output, but this occurs well under reference of *0dB. Considering practically useful output, the ported system extends lower. In the above graph, lowest frequency extension can be raised by a couple of dB with a much larger enclosure, but then it becomes critically damped, and the SPL output of the bass above the lowest frequency range would be reduced further than what it is already.

-Chris

*0dB reference refers to the region where the output is flat. In the above graph, 0dB reference corresponds to 85dB marker.

[Buckle-meister]

Let's examine the average response of the same driver (that has an EPB equally suited to sealed or ported enclosure)

EPB?

Becuase the passive radiator/ported system is a 4th order alignment, it will average 24db/ octave attenuation rate. A sealed system is a 2nd order alignment, thus averaged attenuation rate is 12db/octave.

Does this necessarily mean that the passive radiator/port will sound cleaner than the sealed box due to greater attenuation outwith the F3 point? What I'm trying to say is that beyond the F3 point, the speaker is outwith its (typically) specified range of +-3dB, so isn't a good thing to have the non-cleanly delivered frequencies die away quicker with the passive ratiator/port setup than the sealed box setup?

[WmAx]

EPB?

Sorry, that is a typo on my part. It should be EBP(efficiency bandwidth product). It is a calculation used to determine the suitability of a driver to a specific enclosure type.


Does this necessarily mean that the passive radiator/port will sound cleaner than the sealed box due to greater attenuation outwith the F3 point? What I'm trying to say is that beyond the F3 point, the speaker is outwith its (typically) specified range of +-3dB, so isn't a good thing to have the non-cleanly delivered frequencies die away quicker with the passive ratiator/port setup than the sealed box setup?

One can not so easily attribute terms such as 'sound cleaner' to any particular design based solely upon if it's a sealed or ported design. Many other factors are involved(which I'm going to have to bow out of here, as I am burnt out on this thread at this point) that decide how it 'sounds' in the end. But I will remind you that a ported/passive radiator system's woofer will increase in excursion as frequency lowers substantially beyond the tuned frequency, because their is not an inherant resistive force at this point. A sealed enclosure's air volume stiffness increases as as you go into very low frequencies, reducing driver movement, assuming a non-critically damped alignment.

-Chris

[Buckle-meister]

Thank you. :)

[Buckle-meister]

Question: :rolleyes:

Is the sound heard through earphones identical to what one would hear in an anechoic chamber (i.e. all direct sound + zero reflected sound)? Does this explain why music through headphones is incredibly detailed?

[WmAx]

Question: :rolleyes:

Is the sound heard through earphones identical to what one would hear in an anechoic chamber (i.e. all direct sound + zero reflected sound)? Does this explain why music through headphones is incredibly detailed?

From the aspect of 100 percent of the sound being direct sound, this is true. But the speakers will still provide a degree of spatial effect not possible with the headphones, because the speakers are located in front, at an angle, in relation to your ears/head. The head shape and ear shape will apply a frequency response filtration on the high frequencies, and the left and right channels of speaker sound will cross-mix(you will pick up left channel audio with right ear and you will pick up right channel audio with left ear). Headphones eliminate this effect. Also, resonances will be an issue that have to be considered between headphones and speakers. On a speaker, assuming high quality drivers and crossover, the cabinet is the most difficult part to get right concerning audible resonances. The size/mass of the cabinet on a full size speaker generally makes it expensive to manufacture while preventing audible resonances on conventional designs. Exceptions exist such a open back speakers which make the issue easier/cheaper to deal with. Headphones, being very low mass and small size, are easy/cheap to construct without the risk of problematic resonances of the frame/rear enclosure(homologous to the cabinet of a speaker). The headphone and speaker can be equally free of resonances, but it's much easier/cheaper to accomplish with headphones. However, in an anechoic chamber, resonances are less audible than in a regular reflective room. Resonances are [1]easier to detect when the signal is repeated/delayed. So, along with the inherant simple/small size construction of a headphone that makes reduction of resonances easier in the first place, they are in essence equal to listening to speakers in an anechoic chamber, so any resonances that are present are even more difficult to detect as compared to reflective/live environment. This must also be weighted/considered.

-Chris

[1]The Modification of Timbre by Resonances: Perception and Measurement
Floyd Toole, Sean Olive
JAES, Vol. 36, No. 3, 1988, March, pages 122-141

[Buckle-meister]

...the speakers will still provide a degree of spatial effect not possible with the headphones, because the speakers are located in front, at an angle, in relation to your ears/head.

Yes, it's odd isn't it? When listening to music through headphones, the music is in the centre of your skull. 'Tis a strange concept; people singing inside my head! :D

[Buckle-meister]

I've been thinking a little more on x-db/octave slopes.

I understand that the crossover in a speaker directs frequencies from x to y to say the tweeter and from y to z to say the woofer (in this example consider the speaker a two-way design).

Is it the crossover type that dictates the rolloff of the drivers? If so, what governs the decision to use a 12dB/octave crossover as opposed to say a 24dB/octave crossover? What I'm getting at, is that I would have thought that the theoretically perfect multi-driver speaker would have a brick-wall crossover between the drivers so they didn't overlap a portion of the frequency response. But if this were so, speaker manufacturers would simply always use the x-dB/octave crossovers with the greatest slope that they could, no?

...the passive radiator/ported system is a 4th order alignment, it will average 24db/ octave attenuation rate. A sealed system is a 2nd order alignment, thus averaged attenuation rate is 12db/octave.

What does 2nd order/4th order mean? Is there a first/third/fifth etc?

[WmAx]

Is it the crossover type that dictates the rolloff of the drivers?

Yes, the crossover, but also the natural acoustic rolloff of the drivers contributes. The crossover is integrated with the acoustic rolloff to achieve a final target response. For example, if driver X has a natural 6dB/octave roloff after 4kHz, and you want to low pass this driver at 4kHz, the natural rolloff is going to coincide with part of the electrical crossover's bandwidth. This means that if the final target response is 12dB/octave, that the electrical crossover will be 6dB/octave, becuase the natural rolloff will cascade with the electrical rolloff to provide a final effective target attenuation of 12dB/octave. This is over-simplifying things, but it is a fair summary.

If so, what governs the decision to use a 12dB/octave crossover as opposed to say a 24dB/octave crossover?

This is an engineering matter. It's like asking why use aluminum in one application vs. magnesium in another. It's a complex matter that must be addressed within a specific scenario, weighting the target objectives.

What I'm getting at, is that I would have thought that the theoretically perfect multi-driver speaker would have a brick-wall crossover between the drivers so they didn't overlap a portion of the frequency response.

(1) The steeper the roll-off, the more complex/expensive the passive crossover becomes.

(2) An analog brick-wall filter would create audible phase distortion if used in the lower midband range of frequencies.

(3) A linear phase FIR digital brickwall filter could be used that has no phase distortion, but this is only true for the on-axis response. Off axis(a driver's amplitude/phase response is not the same as you move around it's axis), a very odd pre-ring phase distortion will occur on almost all speakers. The extent of this effect on reflected soundfield in the room and the perceptual weighted effect has not been investigated with credible preceptual research as of this point, at least not of which I am immediately aware. Therefor I can not comment on the effect this will have on sound quality. However, in a situation where the speaker is used where no reflected/off axis sound is contributing the final response, this is a viable method of crossover.


What does 2nd order/4th order mean? Is there a first/third/fifth etc?

For simplicity's sake, you can interpret each 'order' to mean '6dB/octave'. Therefor, 1st order is 6dB/octave, 2nd order is 12dB/octave, 3rd order is 18dB/octave, etc..

-Chris

[Buckle-meister]

Many thanks. I understand. :)

[bigpapa]

The Spring on a Weight analogy really hit it for me and helped me understand.:cool:

Awesome exchange guys (and skirts). Of course, this only creates more questions. I'll divert to another thread so to not derail this one.

[Buckle-meister]

This has become something of a pet thread of mine...:)

Two questions:


When speaker manufacturers build cabinets as massive as they can and/or stiffen the cabinet internally, I understand this is to try and minimise as much as possible the colouration a vibrating cabinet adds to the sound from the drivers alone. Am I right in saying that it's not that the vibrating cabinet is bad in its own right, i.e. if we could somehow mute the drivers yet allow the cabinet to continue vibrating we'd not actually hear sound from the cabinet, but that instead it's the interaction of cabinet vibration with driver motion that causes us not to hear what the driver on its own is attempting to reproduce?
Assuming a speaker is considered as the sum of three components; the drivers, cabinet and crossover, what proportion expressed as (approximate) percentages do each contribute to the final sound that leaves the speaker? In other words, are the proportions analogous to the room/speakers/hi-fi (respectively?) where the room has enormous influence and the speakers and hi-fi far less?

[zumbo]

This is great thread. I am not as educated in the field as the people in this thread, but I do have a few opinions.

A curved or odd shaped cabinet is the best design.

Each speaker in it's on sealed section is the best design.

The crossover design/quality/match is extremely important. Great drivers can sound like crap with a poor crossover.

I am not a fan of passive radiators or ports. But, my speakers and sub are ported.:(

Driver arrangement is also important.

I like this idea:http://www.gr-research.com/images/maplepair.jpg

My Quarts:
http://i47.photobucket.com/albums/f174/zumbo02/MBQ830.jpg

While I did skim some of this thread, I didn't see the properties of a 2 & 1/2 way speaker such as mine mentioned. The two mids share most of the midrange, while the top mid gets a higher rolloff, and the lower mid makes it to the lowest freq spec of the speaker. While not the best technical explination, you can get the idea.

[Buckle-meister]

Zumbo, you've just caused me think of something else: :)

Once its 'latitude', diameter and length are calculated, does it matter whether a port is on the front or rear face (assuming these are of identical width) of a speaker?

[Sheep]

This has become something of a pet thread of mine...:)

Two questions:


When speaker manufacturers build cabinets as massive as they can and/or stiffen the cabinet internally, I understand this is to try and minimise as much as possible the colouration a vibrating cabinet adds to the sound from the drivers alone. Am I right in saying that it's not that the vibrating cabinet is bad in its own right, i.e. if we could somehow mute the drivers yet allow the cabinet to continue vibrating we'd not actually hear sound from the cabinet, but that instead it's the interaction of cabinet vibration with driver motion that causes us not to hear what the driver on its own is attempting to reproduce?
Assuming a speaker is considered as the sum of three components; the drivers, cabinet and crossover, what proportion expressed as (approximate) percentages do each contribute to the final sound that leaves the speaker? In other words, are the proportions analogous to the room/speakers/hi-fi (respectively?) where the room has enormous influence and the speakers and hi-fi far less?


1.) That cabinet would have to compensate for EVERYTHING the driver did. If it was a subwoofer, it would have to act like a passive radiator. I was at FS the other day looking at the car subs, and one dolt wired the drivers in the same box out of phase. The subwoofer made no noise (barely) because one driver was compensating for the others movement.

2.) I would say drivers, crossover, then cabinet.

SheepStar

[Sheep]

While I did skim some of this thread, I didn't see the properties of a 2 & 1/2 way speaker such as mine mentioned. The two mids share most of the midrange, while the top mid gets a higher rolloff, and the lower mid makes it to the lowest freq spec of the speaker. While not the best technical explination, you can get the idea.

I think WmAx explained this at one point. It has something to do with dispersion and cancellation, and having a tapered crossover solves this problem. The Energy Veritas line uses these style crossovers.

SheepStar

[Buckle-meister]

A couple of things Sheep;

That cabinet would have to compensate for EVERYTHING the driver did. If it was a subwoofer, it would have to act like a passive radiator.

It sounds as if you're assigning the greatest importance to the cabinet here but...

I would say drivers, crossover, then cabinet.

Then you say that you reckon the cabinet's the least important. :confused:

Also, what about those percentages (even if rough)? For all I know, they could as easily be 33%, 33% and 34% as 90%, 6% and 4%...

[Sheep]

A couple of things Sheep;

It sounds as if you're assigning the greatest importance to the cabinet here but...

Then you say that you reckon the cabinet's the least important. :confused:

Also, what about those percentages (even if rough)? For all I know, they could as easily be 33%, 33% and 34% as 90%, 6% and 4%...

How many wood cabinets act like a passive radiator? As far as sound goes, the drivers are the first in the list, maybe 55%. The response of the speaker is determined by the drivers.

Next, the crossover has to split the 2 drivers at the right spot. Also very important for the sound. 25%

While I put the box last I didn't mean it was useless. That said, any 3/4inch MDF enclosure with some polly fill and bracing will suffice for a speaker. Subwoofers might need more, but in general, you can get away with the earlier. 20%

Edit: For your first remark, that whole question was based on the cabinet affecting the sound. Obviously I would stress the importance of the cabinet in that role.

SheepStar

[WmAx]

T
When speaker manufacturers build cabinets as massive as they can and/or stiffen the cabinet internally, I understand this is to try and minimise as much as possible the colouration a vibrating cabinet adds to the sound from the drivers alone.

Am I right in saying that it's not that the vibrating cabinet is bad in its own right, i.e. if we could somehow mute the drivers yet allow the cabinet to continue vibrating we'd not actually hear sound from the cabinet, but that instead it's the interaction of cabinet vibration with driver motion that causes us not to hear what the driver on its own is attempting to reproduce?

Incorrect. The cabinet baffles, of an average speaker, will have substantial acoustic output. The majority of output is limited to the specific resonances of the panels. The contribution of this will alter the percieved timbre of the speaker, the degree of which, is determined by the amplitude, frequency and bandwidth(Q) spread of the effect(s). There are numerous ways to prevent the cabinet from producing appreciable acoustic output: high level of mass loaded dampening on walls, exotice low resonance construction materials, massive structure that is very heavily braced to spread resonant frequencies to a spectrum that is not very important, efficient lower mass structural design to the same, mechanical decoupling system(s), or a combination of these.


Assuming a speaker is considered as the sum of three components; the drivers, cabinet and crossover, what proportion expressed as (approximate) percentages do each contribute to the final sound that leaves the speaker?

It is an equal distribution: the failure of one will compromise the entire system.

-Chris

[WmAx]

Once its 'latitude', diameter and length are calculated, does it matter whether a port is on the front or rear face (assuming these are of identical width) of a speaker?

On a midbass application, the port may output mid frequency resonances/noises. There for, it is preferable to have the port fire from the rear on such application(s).

-Chris

[WmAx]

While I put the box last I didn't mean it was useless. That said, any 3/4inch MDF enclosure with some polly fill and bracing will suffice for a speaker. Subwoofers might need more, but in general, you can get away with the earlier. 20%



The cabinet resonances fall in the spectrum of the midrange. There for, it is rarely a consideration of resonances, that one has to account for a subwoofer. Not just 'any' 3/4" MDF enclosure will be suitable. The bracing must be intelligently designed to shift/distribute the resonances to a minimal contribution. Another option is to use large amount(s) of mass loaded dampening materials on the walls such as Dynamat. However, it should be noted that a single layer is not sufficient. You will have to use such material at 1/4-1/3 the thickness of the MDF walls in order to achieve optimal effect. This can contribute significantly to cost, depending on the size of the cabinet. However, it is possible to use some alternatives, such as roofing materials, in the same capacity at a somewhat reduced cost.

-Chris

[Buckle-meister]

Incorrect. The cabinet baffles, of an average speaker, will have substantial acoustic output.

Interesting. I never thought it'd be so bad as to be audible, even on a less than 'average' speaker. Oh well. Live and learn. :)

It is an equal distribution: the failure of one will compromise the entire system.

I understand that, but I could just as easily say that failure of the speakers will compromise the entire system (in other words no sound at all!) in my room/speakers/hi-fi analogy. What I'm trying to get an appreciation of is what, assuming all parts are working, the relative importance of each is. With this in mind, do you still say they're all of equal importance?

Another option is to use large amount(s) of mass loaded dampening materials on the walls...

Like the material 'grania'?

[WmAx]

Interesting. I never thought it'd be so bad as to be audible, even on a less than 'average' speaker. Oh well. Live and learn. :)

In fact, the output is so high from lower quality floor standing speakers, that you can play music, lean your ear very close to the enclosure panels(almost touching), and hear the narrow midband contribution of the cabinet from the side panels. Now realize the large surface area of the total panel area. This contributes significant radiation. Think about this related issue, for a similar phenomenon: If someone has a stereo playing in the room next to you, and the door is closed, you can still hear it THROUGH THE WALL. That is usually 2 layers of 1/2" drywall(a fairly well dampened material) between you and the sound source. The majority of the sound is caused by the resonant modes of the structure(s) and wall(s). If you notice, the majority sound that breaches is not full range, but is distributed in narrow bands. Most of the full range breach is caused by air breaches between the the room you are in and the source room.



I understand that, but I could just as easily say that failure of the speakers will compromise the entire system (in other words no sound at all!) in my room/speakers/hi-fi analogy. What I'm trying to get an appreciation of is what, assuming all parts are working, the relative importance of each is. With this in mind, do you still say they're all of equal importance?

It will be up to you to define your weighting. My response was meant to apply to hi-fidelity reproduction, not basic operation. The connection wire is critical for basic operation....

Like the material 'grania'?

I am not familar with a material by that name.

-Chris

[zumbo]

On a midbass application, the port may output mid frequency resonances/noises. There for, it is preferable to have the port fire from the rear on such application(s).

-Chris

I agree. Even on a sub. If there is to be a port, I prefer it in the rear. Mainly, because I just don't like the nasty sounds that can come from them.

[Sheep]

I agree. Even on a sub. If there is to be a port, I prefer it in the rear. Mainly, because I just don't like the nasty sounds that can come from them.

It doesn't matter where they fire, you will hear port noise.

SheepStar

[zumbo]

It doesn't matter where they fire, you will hear port noise.

SheepStar

I agree. That is why I prefer a sealed design. I do believe "rear firing" will cancel-out some of that noise, or smooth it out.

[Buckle-meister]

On a midbass application, the port may output mid frequency resonances/noises. There for, it is preferable to have the port fire from the rear on such application(s).

It doesn't matter where they fire, you will hear port noise.

I agree. That is why I prefer a sealed design. I do believe "rear firing" will cancel-out some of that noise, or smooth it out.

Why are some ports placed on the front then? Is it purely for aesthetics?

It will be up to you to define your weighting.

Bah!

I am not familar with a material by that name.

Sorry WmAx, :o I meant Granitech (http://www.mission.co.uk/pigs/pigpilastro.pdf) (you'll need to scan through the text a little).

[zumbo]

Why are some ports placed on the front then? Is it purely for aesthetics?

Not sure. I have a guess. Let's say the speaker maker designed the speaker to reproduce sound a certain way. If the port is in the rear, there would be a bigger difference in sound depending on placement and room acoustics. I would think it would be much harder to guess what the sound would be during building and testing. No real way to design the speaker to sound a certain way.

Now, with a front port, I think it's a little different. The sound would change much less with placement and room acoustics. It is still a factor, but I would think it would be much less of one. So, the speaker would sound closer to the sound intended when used in different applications.

Shorter explanation. A front ported speaker may be easier to place due to room acoustics.

[Buckle-meister]

Shorter explination. A front ported speaker may be easier to place due to room acoustics.

Argh! Now you've gone and raised the opposite question; if the above is true, why don't speaker manufacturers always place ports on the front? After all, a speaker that sounds fabulous independant of a room's acoustics sounds like it'd be the Holy Grail to speaker manufacturers to me.

[Sheep]

Buckle, relax, we need you breathing :D

I have used front and rear firing subs (2 front, 1 rear) and the front firing ones gained very little from corner placement. That rear firing sub sounded different IMO. It excited differnt room modes, or something, because the output changed drastically. The Athena AS-P400 and Velodyne DPS-12 had a similar style response in my room while in the same spot. Ofcourse the Velodyne went down lower and had a different sound characteristic, but the peaks and valleys seemed to be in the same spots.

Take this with a grain of salt.

Maybe I will flip my sub around and tell you how it sounds, if you're nice. :rolleyes:

SheepStar

[zumbo]

Argh! Now you've gone and raised the opposite question; if the above is true, why don't speaker manufacturers always place ports on the front? After all, a speaker that sounds fabulous independant of a room's acoustics sounds like it'd be the Holy Grail to speaker manufacturers to me.

Probably because the reasons listed about the nasty port sounds you can get from time-to-time. I am pleased with the ports on my towers, but not so pleased with the port on my sub(at HIGH volumes).

Let's look at the favorite design features I listed.

Sealed: Much more power is needed. The consumer has to invest in a high-power amp. There is a better market for speakers that can run off of a 100w receiver.

Curved or odd shaped cabinets: (a)More expensive to build. Have to pass the cost on to the consumer. (b)You can do some fancy work inside the cabinet and achieve similar results.

High-quality crossover network: See #2(a).:D

IMO, the best speakers are sealed, curved or odd shaped, and expensive. There is just not much of a market for that.:( But if one were to build their own, this is what I would do.;)

[WmAx]

If the port is in the rear, there would be a bigger difference in sound depending on placement and room acoustics.

Placing a port on an opposite side as the driver only makes placement a bigger problem due to logistics: You can't put the speaker right up against a wall because it will obstruct the port. Other than this, of course, you are moving part of the LF response the distance of the enclosure depth away from where a front port would create sound. Any change in posisition in the room will affect the LF interaction(s) in some way (magnitude of which is depedant in particular circumstances), so of course the same speaker with a front port as compared to the same speaker with a rear port, would sound different in the same spot.

-Chris

[WmAx]

It doesn't matter where they fire, you will hear port noise.

SheepStar

A subwoofer that creates audible port noise[chuffing] during normal operation is poorly designed. A midrange/midbass enclosure that creates audible port noise will be a different type of noise; being a narrow band of frequencies reflected/resonated in the tube. This varies in actual severity(is it audible in a particulare case, for example). But the majority of frequencies created in either case(subwoofer or midrange/midbass) will be high enough in frequency that the width of the cabinet will be substantial in relation to the frequency wavelength in air. There for, you can redirect the noise, and it will attenuate/diffuse to some degree before arrival, as compared to being a directly radiated from the front of the cabinet.

-Chris

[Buckle-meister]

Speaker manufacturer's frequency response specifications are virtually always stipulated on-axis (though I believe that some stipulate additional, off-axis responses.

I know that people commonly 'aim' speakers slightly past them, so clearly good off-axis response is an advantageous property for a speaker to possess. Or is it?

If a speakers off-axis response isn't particularly good, why not simply turn the speaker so that it faces you directly? The front soundstage might alter a little, but ignoring room acoustics for the sake of simplicity, at least you'd be back to within ±3dB.

[WmAx]

I know that people commonly 'aim' speakers slightly past them, so clearly good off-axis response is an advantageous property for a speaker to possess. Or is it?
Consistent off axis response is very important if you want to have a consistent tonal balance across more than a single listening spot. Off axis response is critical to sound quality [as demonstrated in published perceptual research studies] in situations where room acoustics are a variable, as has been discussed in other threads.

If a speakers off-axis response isn't particularly good, why not simply turn the speaker so that it faces you directly? The front sound stage might alter a little, but ignoring room acoustics for the sake of simplicity, at least you'd be back to within ±3dB.

Yes, for the direct arrival sound, this is a solution. But it does not solve the problem of the uneven sound balance radiated into the ambient field. If you have treatments approaching the level found in an audio control room, then obviously, off axis response is of little concern so far as the room ambient field is concerned.

-Chris

[nfrnoman]

Is anyone out there aware of a component that converts traditional sound signal to multi-tonal vibration? I'm struggling to locate such an item and thought I might go fishing in the forums. Thanks.

[Buckle-meister]

For my next two questions, :rolleyes: I first need to give a bit of background information.

I currently have Mission's Elegante e82 system in 5.1 configuration. My curent surround speakers are therefore the e80s, the specification for which maybe found here (http://www.mission.co.uk/pigs/e82_system_flyer.pdf).

At some point in the future I'll be upgrading to a 7.1 configuration and maybe a 9.1 configuration. However, instead of buying 2 additional e80s for the surround-backs or 4 for surround-backs and presence, I am considering buying up to 4 of the larger e81s from Mission's larger e83 system, the specifications for which may be found here (http://www.mission.co.uk/pigs/e83_system_flyer.pdf). If I do, then my little e80s would be perfect for use as the presence channels.

Note: I am not looking for advice on various brands of speaker to buy. I will definately be getting either the e80s or e81s as I want them to be in keeping with the look of my existing speakers (not to mention that they'd be timber matched).

So, my questions are:


How can it be that a speaker (e81) which has more drivers in it than another (e80) can be easier to drive? Why isn't the opposite true that the e81s require more power due to their additional driver when compared to the e80s?
Somewhat along the same lines, how is it that the lower bound figure for the e81's frequency response is the same as that of the e80s? If there're more drivers in the former why aren't they able to extend lower than the latter?

[Sheep]

1.)How can it be that a speaker (e81) which has more drivers in it than another (e80) can be easier to drive? Why isn't the opposite true that the e81s require more power due to their additional driver when compared to the e80s?

2.)Somewhat along the same lines, how is it that the lower bound figure for the e81's frequency response is the same as that of the e80s? If there're more drivers in the former why aren't they able to extend lower than the latter?

1A. More drivers equals more sound. I think adding an extra driver will give you a 2dB boost (if the crossover is right). The e81 can handle more power though.

2A. That would depend on the cabinet, tuning, etc.

SheepStar

[Buckle-meister]

Hello all (again ;)),

Out of curiosity I clicked Audioholics' home page's link to the Axiom speaker package and more specifically the frequency response of the EP600 (http://www.axiomaudio.com/ep600_main.html#) subwoofer (scroll down and click on 'Graph' on the left hand side of the page). I couldn't help but notice that for all intents and purposes, the graph falls off in a straight line below the natural limit of the driver.

Now, I'm not picking on this speaker in any way. I only chose it because it was handy. Any plot for a woofer would, I suspect, be similar but for the driver's limits moving further up or down the scale. My question is:

Why does the response fall off in an almost straight line? If a driver reaches its lower limit and then progressively struggles to output at the same SPL, why doesn't the graph show a slowly, but progressively steepening curved response falling off (such as in the attached plot below)?

[Sheep]

Is that just a driver or a driver in a box?

When a driver isn't in a box (IE: Free Air) the back waves cancel out the front waves (in the low end). Thats why it rolls off steeper.

SheepStar

[Buckle-meister]

Is that just a driver or a driver in a box? When a driver isn't in a box (IE: Free Air) the back waves cancel out the front waves (in the low end). Thats why it rolls off steeper.

The Axiom's response, which is the steeper of the two, is in its own enclosure.

[Sheep]

The Axiom's response, which is the steeper of the two, is in its own enclosure.

Is it sealed? Looks similar to a sealed roll off in an anechoic chamber, but it rolls earlier then I've seen.

SheepStar

[Buckle-meister]

Is it sealed?

The axiom's enclosure is not sealed.

[Sheep]

The axiom's enclosure is not sealed.

Then..


EWWWW!

SheepStar

[WmAx]

Hello all (again ;)),

Out of curiosity I clicked Audioholics' home page's link to the Axiom speaker package and more specifically the frequency response of the EP600 (http://www.axiomaudio.com/ep600_main.html#) subwoofer (scroll down and click on 'Graph' on the left hand side of the page). I couldn't help but notice that for all intents and purposes, the graph falls off in a straight line below the natural limit of the driver.

Now, I'm not picking on this speaker in any way. I only chose it because it was handy. Any plot for a woofer would, I suspect, be similar but for the driver's limits moving further up or down the scale. My question is:

Why does the response fall off in an almost straight line? If a driver reaches its lower limit and then progressively struggles to output at the same SPL, why doesn't the graph show a slowly, but progressively steepening curved response falling off (such as in the attached plot below)?

The Axiom graph is perfectly normal for a ported system. The graph that you attached to your forum post is probably a sealed system. A ported system attenuates at *24 dB/octave compared to *12 dB/octave for a sealed system. Also, your attached graph is not comparable to the Axiom graph. Please note the dB scales of both graphs.

*Note: The actual attenuation rate at any given point can vary dramatically, depending on the specific box alignment used. For example, one can design a non-conventional ported system with the roll off characteristic of a sealed system for much of it's attenuation range, only beginning to attenuate more rapidly at the lowest limits.

-Chris

[Sheep]

Hey ya, thats not even the right graph...


http://www.axiomaudio.com/global/images/diagrams/EP600_graph.gif

Thats the EP600..

SheepStar

[Buckle-meister]

First of all, sorry for the delayed response WmAx. Last time I looked at the thread, Sheep hadn't a clue. :D

...your attached graph is not comparable to the Axiom graph. Please note the dB scales of both graphs.

Shoot! Yes, I should've spotted that myself. Sorry 'bout that. :(

So, given that roll-off exhibits a non-linear slope (x-dB/Octave = linear decrements of dB for a halving of frequency), is it correct to say that when the scales/limits of graphs that're being compared are compatible, both the theoretical and actual response (with the latter a little more 'ragged' looking) would be a straight line plateaux and at its lower end; a smoothly (with ever increasing slope) curved roll-off?

EDIT: Shoot! Just remembered that the response is typically plotted using a logarithmic scale!

Also, regarding speaker drivers, now and again I hear of folk talk of perfect driver motion as being 'pistonic'. Now I know what a piston is, but I was wondering whether what was meant by pistonic literally referred to the same type of motion as a car engine's pistons where the locus of the cylinder head over time would show a sinusoidal curve, or whether what was meant was a square-wave type of graph of a perfect driver moving backwards and forwards over time?

[jaxvon]

First of all, sorry for the delayed response WmAx. Last time I looked at the thread, Sheep hadn't a clue. :D



Shoot! Yes, I should've spotted that myself. Sorry 'bout that. :(

So, given that roll-off exhibits a non-linear slope (x-dB/Octave = linear decrements of dB for a halving of frequency), is it correct to say that when the scales/limits of graphs that're being compared are compatible, both the theoretical and actual response (with the latter a little more 'ragged' looking) would be a straight line plateaux and at its lower end; a smoothly (with ever increasing slope) curved roll-off?

EDIT: Shoot! Just remembered that the response is typically plotted using a logarithmic scale!

Also, regarding speaker drivers, now and again I hear of folk talk of perfect driver motion as being 'pistonic'. Now I know what a piston is, but I was wondering whether what was meant by pistonic literally referred to the same type of motion as a car engine's pistons where the locus of the cylinder head over time would show a sinusoidal curve, or whether what was meant was a square-wave type of graph of a perfect driver moving backwards and forwards over time?


You'd want pistonic in the automotive sense. The goal of any driver is to track the incoming sinusoidal signal as precisely as possible. Now, keep in mind that the musical signal will look almost nothing like a single tone sine wave, as music consists of hundreds if not thousands of different waveforms of differing frequencies and amplitudes summed into a single signal (one for each channel). Your speakers' drivers must then move as best they can to replicate that wave. To better stress the point, I've included a simple visual.

Here is your basic sine curve with amplitude A:

http://users.uma.maine.edu/faculty/rsm/slides/chap4/f4-3a.gif

If you are playing a test tone of say, 1kHz, the input should look like the above graph. The equilibrium of a sine curve is the line where A=0. In the above graph this line is the t axis. This is where the greatest rate of change takes place. How does this translate to driver movement? With an input of voltage V and current I, a driver will exhibit a given output that corresponds to that input. The movement of the driver can be expressed by the same sine wave. When the driver is at rest, it is sitting at the equilibrium point. When moving with input signal of f=1000Hz, it should ideally move back and forth, perfectly tracking the sine wave, with the greatest velocity occuring when the driver passes the equilibrium point during its stroke.

[Buckle-meister]

You'd want pistonic in the automotive sense. The goal of any driver is to track the incoming sinusoidal signal as precisely as possible...Your speakers' drivers must then move as best they can to replicate that wave.

Are you sure? Aren't we getting confused by what the input signal to the driver is versus what behaviour we would ideally have the driver possess?

I understand that music can be built up from the sum of a multitude of sine waves - this is the basis of digital recording is it not. However, say we introduce a square wave to a driver, unless I am mistaken, the driver will not be able to play it perfectly because the simple act of moving backwards and forwards will lend the driver momentum (which does not form a part of the input) and so the 'square' part of a square wave input cannot faithfully be reproduced. In other words, even when the input stops, because of momentum no driver can ever stop at the same instant.

Now consider the opposite case. Here we have a (theoretical) driver that can exactly reproduce a square wave type input. Such a driver would have the capacity to 'turn on a hair's breadth' so to speak would it not? Thus my argument that pistonic driver motion would actually take a square wave form in terms of driver capacity, but that it is the source input of sound that is (comprised of) sinusoidal (components).

Does this make sense, :confused: or is it still completely wrong? :D

[ChrisJam]

Just for reference, it's spelled "ya'll". Keep in mind that "ya'll" is singular. The plural of "ya'll" is "all ya'll" :D


I may be a newbie to HT and its related components, but now we're in *my* ballpark! <cue evil laugh: muhahaha> :D

As a full-time writer who does some freelance editing, I can assure you that the correct spelling is "y'all." The contracted word is "you," which puts the apostrophe between "you" and "all."

Don't belive me? No problem! :) Check this well-respected American English usage book: _Garner's Modern American Usage_, from the Oxford Press, 2003. Even my handy-dandy desktop dictionary has "y'all," not "ya'll."

You are right--well, almost <s>--about the plural. It involves another "all": the plural is "all y'all." Now it gets fun if we go to the possessive of the plural: "all y'all's."

OK, enough of the off-topic stuff. I now return control of your TV set to you. (Oops, I was having an "Outer Limits" moment.)

BTW, jax, I'll probably be asking more audio newbie questions, and look forward to having you help me again. Best wishes! :)

[ChrisJam]

I saw strange lines in the bottom part of my reply, and tried fixing them. It didn't work. But you can read my words, which shouldn't have had any strike-out lines through them. I don't know where they came from. Maybe this is something else I can learn from the audiophiles at this forum. :-)

[ChrisJam]

Mulester7 told me in a PM how to remove my double post. I took the advice and, voila, the extra post is gone. Thanks! I still don't know where the strike-out lines in my original post came from. I hope it's as readable on your computers as it is on mine.

But hey, I'm still right about the spelling of "y'all." :D


Chris

[WmAx]

So, given that roll-off exhibits a non-linear slope (x-dB/Octave = linear decrements of dB for a halving of frequency), is it correct to say that when the scales/limits of graphs that're being compared are compatible, both the theoretical and actual response (with the latter a little more 'ragged' looking) would be a straight line plateaux and at its lower end; a smoothly (with ever increasing slope) curved roll-off?

You may have to clarify what you wish to inquire about. But if you are asking if the graphs shown are correct(as would be expected to be predicted by a typical calculation), then yes, they are.

Also, regarding speaker drivers, now and again I hear of folk talk of perfect driver motion as being 'pistonic'. Now I know what a piston is, but I was wondering whether what was meant by pistonic literally referred to the same type of motion as a car engine's pistons where the locus of the cylinder head over time would show a sinusoidal curve, or whether what was meant was a square-wave type of graph of a perfect driver moving backwards and forwards over time?

So far it seems that the typical/common reference to pistonic is not being used in this thread in the correct perspective. When one refers to 'pistonic' behaviour, they usually mean a diaphragm that moves as a single, solid unit. In real life, most diaphragms have a degree of flex due to stress past a certain frequency[where the driver enters break-up mode(s)], or when the driver is under very great pressure/stress(such as a LF driver at high excursion/incursion) where the stress exceeds the mechanical stiffness to retain a solid shape. The edges of the diaphragm will not be moving in exact unison/phase with the center, for example.

-Chris