Properties of Speakers

[Buckle-meister]

I remembered.

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

Where'd you read that?

'Twas here 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.

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. 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.

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:

 

[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?

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?

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:

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:

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?