Myths about subwoofers

[haraldo]

Here is another site I just came across and it has some fantastic articles written by Carl Kennedy “the Alchemist”.

Some very informative stuff, and very well written, as well as having a excellent well put together site...

Take some time and enjoy his site...
http://theprofessionalanswer.com/WordPress/

Great stuff

 

[snappy_snoopy]

Great stuff

wicked i spent some time reading as well, very informative.

FUNNY how those who advertise well can have really bad products and those who produce brilliant equipment no one ever hears of. Funny a particular brand comes to mind that starts with "B" and ends with "ose".

Dad uses one of their systems, if only i found you website in time to save him the dissapointment.

 

[mtrycrafts]

wicked i spent some time reading as well, very informative.

FUNNY how those who advertise well can have really bad products and those who produce brilliant equipment no one ever hears of. Funny a particular brand comes to mind that starts with "B" and ends with "ose".

Dad uses one of their systems, if only i found you website in time to save him the dissapointment.

Well, if your dad is not a critical listener, most likely he likes what he has for his casual enjoyment, no?

 

[jamesnicholes]

subwoofers

Cool Stuff.............................man

 

[2wired]

Great info!

 

[highfigh]

This is certainly a very good read, there are just a few things I wonder about though.

• 
  I have always had the impression (using my ears) that sealed box subwoofers sound better and more natural than ported subwoofers, in general, it's hard to be 100% firm on this, because there a well designed and poor designs in both camps, but fur music, I would pick a sealed sub

• 
  I'm getting the impression from this article that driver size is unimportant, if you look at the physics, I don't seem to undertand that.... An 18" driver generally has like 3 to 5 times the mass of a 10" driver, and if you have to pair the sub with satellites with 4" bass/mid drivers, I don't think the 18" will provide for a good match

• 
  A ported subwoofer will have a much more significant phase aberration and group delay compared to a sealed box, because of the much sharper roll off..... Whether this is audible or not...... People might start a war on this subject...... I certainly know that it's a fact, but whether it's important or not should probably be up to each of us to sort out. If you can hear a difference, then it may be important.
  Personally I believe this may make a difference.

Regards

Harald N

1) As the list stated, the Qts (can be derived through (QesxQms/Qes+Qms) makes a huge difference. A Qts of 1 (small sealed or decently tuned vented box) will be slightly boomier than a Qts of .7 (generally considered "correctly tuned" sealed box), which tends to be good for many kinds of music. A Qts of more than 1.5 is kind of a "one note wonder" and is really good for some kinds of source material, like Rap and Hip Hop but doesn't work well for rock, pop, jazz or classical. A really low Qts is considered "dry" sounding because the notes hit and die away almost immediately. I have seen Qts=.707 called "critically damped".

If you want to think of the effect of low, medium and high Qts, a low Qts affects a broader frequency range and falls off at less dB/octave and a high Qts is like an undamped drum head that rings at one frequency, with much less at neighboring frequencies. This link shows this:
http://en.wikipedia.org/wiki/Image:Resonance.PNG

2) A small, correctly tuned driver/enclosure can reproduce very low frequencies. You may not hear them in a large room or from a great distance, but it can do this. A speaker just makes air vibrate and a larger one will do it more, but in the wrong room, tuning or enclosure, it won't do it well. It is all about matching efficiencies, sensitivity, room volume and how a given system works within a certain volume of air. A cone with high mass requires a large force to get it to accelerate quickly and it also needs another large force to bete it to stop again. Lighter cones have the advantage here- if it accelerates/decelerates easily, the motor assembly will be more faithful to the signal, within the parameters of the thermal compression mentioned. Once the motor can move accurately, it's a matter of getting the air in the box, port and room to cooperate and work together. Listen to a really good car stereo (not one designed for the SPL contests) and make note of the speaker size. Many of the really good sounding ones will have 6-1/2" - 10" woofers and they hit very low frequencies because of how the interior volume of the car works with the sound from the speakers. Open the window and the frequency response changes considerably because you have just created a bandpass enclosure.

3) The rear of the pressure wave comes out through the port and of things aren't right, the phase relationships won't be, either. The phase cancellations will be a comb filter and it can be really ugly.

 

[highfigh]

Whether you go sealed or ported depends on the parameters of the driver you are working with. A sealed enclosure will have an F3 somewhat above Fs, but roll off will be 12db per octave. However with sealed to get good output at 20 Hz some Eq is going to be required, and that raises the specter of thermal compression.

The ported enclosure can have F3 very close to Fs. I agree there will be some phase and time delay problems below Fb, but I think these are not highly objectionable. You can tune a ported enclosure so the bass does not splash all over the place. The other problem with ported enclosures is that the driver rapidly decouples below F3 so you can easily bottom the driver without a subsonic filter. So it is swings and roundabouts.

I personally favor the TL for the most natural bass, however TLs with F3 down in the low 20 Hz range occupy significant real estate. The support is broad however, and roll of 12 db per octave. I have found that TLs with F3 in the neighborhood of 25 Hz really give you bass you can feel without advertising it, and touch lightly until there is serious program in that range.
Once people experience bass from a TL they seldom go back to anything else. Dual lines tuned 1/2 octave apart give nice smooth natural bass over 2 1/2 octaves. I'm not sure why, but they just don't boom at all. It is smooth deep even and effortless. So many of my friends notice that.

Nowhere in the formula for deriving F3 is the diameter of the driver relevant directly. However larger cones tend to be heavier, so you have a heavier weight on the spring so to speak. However you can make the spring less stiff and accomplish the same thing. The vintage JW driver, had a four inch tractrix aluminum cone that weighed only six grams. The suspension was unique in that the cone and voice coil were suspended under slung on three long beryllium cantilevers. This JW module was capable of quite astonishing bass reach.

Have you seen this site?
http://www.quarter-wave.com/

Opinions?

 

[WmAx]

1) As the list stated, the Qts (can be derived through (QesxQms/Qes+Qms) makes a huge difference. A Qts of 1 (small sealed or decently tuned vented box) will be slightly boomier than a Qts of .7 (generally considered "correctly tuned" sealed box), which tends to be good for many kinds of music. A Qts of more than 1.5 is kind of a "one note wonder" and is really good for some kinds of source material, like Rap and Hip Hop but doesn't work well for rock, pop, jazz or classical. A really low Qts is considered "dry" sounding because the notes hit and die away almost immediately. I have seen Qts=.707 called "critically damped".

If you want to think of the effect of low, medium and high Qts, a low Qts affects a broader frequency range and falls off at less dB/octave and a high Qts is like an undamped drum head that rings at one frequency, with much less at neighboring frequencies. This link shows this:
http://en.wikipedia.org/wiki/Image:Resonance.PNG

Of course, this is a pure function of frequency response. One can for example, take a woofer and put it in a very tiny sealed box, effecting a Qtc of 2, and it can then be corrected with electronic line level filters to make it in effect a QTC of 0.7 or any other response target. This is the common technique used for sealed commercial subwoofers. The downside is that to make this work well requires a driver with very high excursion that is linear and very high power ability to avoid compression, and of course, a very high power amplifier. This used to be a poor choice overall unless space was at a premium. But today, drivers exist that make it possible to do this and still retain very high performance and very low distortion. Refer to JL's W7 drivers as a popular example. Unfortunately, there are still very few proven (by 3rd party credible analysis/measurement) drivers suited to this application, and they all tend to be rather costly unless you find them on a clearance or other special deep discount pricing.

However, a proper ported design still offers superior performance if the added volume is acceptable in an application and I only recommend sealed systems in very specific situations where it proves an advantage due to the underlying circumstances.

A cone with high mass requires a large force to get it to accelerate quickly and it also needs another large force to bete it to stop again. Lighter cones have the advantage here- if it accelerates/decelerates easily, the motor assembly will be more faithful to the signal, within the parameters of the thermal compression mentioned.

In fact, the only true result of higher mass is lower efficiency. It should be noted, that the highest performance(defined as distortion vs. spl and motor linearity and power compression) subwoofers available today have very high mass cone/VC assemblies.

-Chris

 

[highfigh]

Of course, this is a pure function of frequency response. One can for example, take a woofer and put it in a very tiny sealed box, effecting a Qtc of 2, and it can then be corrected with electronic line level filters to make it in effect a QTC of 0.7 or any other response target. This is the common technique used for sealed commercial subwoofers. The downside is that to make this work well requires a driver with very high excursion that is linear and very high power ability to avoid compression, and of course, a very high power amplifier. This used to be a poor choice overall unless space was at a premium. But today, drivers exist that make it possible to do this and still retain very high performance and very low distortion. Refer to JL's W7 drivers as a popular example. Unfortunately, there are still very few proven (by 3rd party credible analysis/measurement) drivers suited to this application, and they all tend to be rather costly unless you find them on a clearance or other special deep discount pricing.

However, a proper ported design still offers superior performance if the added volume is acceptable in an application and I only recommend sealed systems in very specific situations where it proves an advantage due to the underlying circumstances.



In fact, the only true result of higher mass is lower efficiency. It should be noted, that the highest performance(defined as distortion vs. spl and motor linearity and power compression) subwoofers available today have very high mass cone/VC assemblies.

-Chris

The whole thing is a tightrope balancing act with all kinds of people tugging at the rope. Change one thing a little and it affects the rest. Compensate for something and another change occurs. It's a wonder some things work at all, eh?

Re: heavy assemblies- they also need to have strong drive characteristics and must be matched to the right amplifier for it to work properly. Adding all kinds of circuitry changes the response but can cause other issues. Still, there are a lot of small subs that do more than anyone thought possible, before.

 

[Adzjwarner]

Agreed, i liked this

 

[UT_EE]

Nice article, much appreciated!

 

[Cpyder]

Overall a good read! I feel like the author is speaking in extremes for some of the points though.

"One of the biggest myths about woofers is that 8’s and 10’s are “tighter” and “cleaner” than 15’s or 18’s. Nothing is further from the truth."

Smaller subs do sound tighter, however. It's true that all subs will move at the same frequency for each note but sometimes that note isn't played long enough for the driver to fully respond. If there's a bass hit that lasts for 1/10 of a second, a smaller sub, like a 6.5" driver will be able to respond more accurately because it will be able to accelerate faster than a large sub (like an 18" for example) Over the same time interval the larger sub may not have been able to change it's velocity (accelerate) sufficiently. It's simple physics. Why do you think you use a tweeter for highs and subs for lows. They cannot share jobs.

"So in conclusion, the only reason to use a smaller bass driver is for space, weight and potentially power considerations..."

Does everyone agree with this?

Also, one reason so many people say smaller subs are faster/cleaner etc is because of the same reason a piano sounds different than a violin. It has to do with harmonics. When you play a middle C on a piano and violin, you don't just get a frequency of 263hz (or whatever a middle C is - I think it's around this frequency). You get that note plus all the other harmonics at higher frequencies. Smaller subs have different harmonics than larger ones. Hence, they sound different when playing the same notes as larger ones. This is also one reason why people say larger subs sound "boomy."

"Your subwoofer driver does not have a conscience, and it does not perform better with one type of music over another"

I cannot agree with this. Surely some subs sound better with certain types of music that other subs. I can attest for this myself as I have had 12s, 15s, and 6.5s in my car and certainly thought some songs sounded a lot better with different subs. The 6.5s make my want to blow a load with higher frequency snappiness. And the larger subs, I found, were better with lower, longer bass notes.

Reflect your thoughts. Am I crazy?

 

[TLS Guy]

Overall a good read! I feel like the author is speaking in extremes for some of the points though.

"One of the biggest myths about woofers is that 8’s and 10’s are “tighter” and “cleaner” than 15’s or 18’s. Nothing is further from the truth."

Smaller subs do sound tighter, however. It's true that all subs will move at the same frequency for each note but sometimes that note isn't played long enough for the driver to fully respond. If there's a bass hit that lasts for 1/10 of a second, a smaller sub, like a 6.5" driver will be able to respond more accurately because it will be able to accelerate faster than a large sub (like an 18" for example) Over the same time interval the larger sub may not have been able to change it's velocity (accelerate) sufficiently. It's simple physics. Why do you think you use a tweeter for highs and subs for lows. They cannot share jobs.



"So in conclusion, the only reason to use a smaller bass driver is for space, weight and potentially power considerations..."

Does everyone agree with this?

Also, one reason so many people say smaller subs are faster/cleaner etc is because of the same reason a piano sounds different than a violin. It has to do with harmonics. When you play a middle C on a piano and violin, you don't just get a frequency of 263hz (or whatever a middle C is - I think it's around this frequency). You get that note plus all the other harmonics at higher frequencies. Smaller subs have different harmonics than larger ones. Hence, they sound different when playing the same notes as larger ones. This is also one reason why people say larger subs sound "boomy."

"Your subwoofer driver does not have a conscience, and it does not perform better with one type of music over another"

I cannot agree with this. Surely some subs sound better with certain types of music that other subs. I can attest for this myself as I have had 12s, 15s, and 6.5s in my car and certainly thought some songs sounded a lot better with different subs. The 6.5s make my want to blow a load with higher frequency snappiness. And the larger subs, I found, were better with lower, longer bass notes.

Reflect your thoughts. Am I crazy?

Yes you are under some misapprehensions.

Whether bass is tight or not has nothing to do with driver size, but the total system Qtc. If it is around 0.5 it will be tight. It will be very boomy and muddy over 0.8.

You are also confused about fast bass. A woofer is incapable of producing any attack transient by itself. A sharp transient requires the ability to at least produce a facsimile of a square wave. Even a 20 Hz square wave requires a substantial high frequency component to reproduce it. So fast bass from a sub is in and of itself an oxymoron. Any sub cut in below 80 Hz, is incapable of producing a transient by itself. The reason is that if you do Fournier analysis the sharp up stroke of even a very low frequency has a strong high frequency component.

There for the sharp attack comes from a sub with low Qtc integrated well with the other speakers. In fact the later is very hard to achieve. That is why I have designed and built true full range speakers and go subless. If you click on my signature you will see the speakers.

On an SACD of the opening of Aho's symphony number 12, there is a lot of Laplander rhythmic drumming, that requires superb bass attack. I'm unable to get even very expensive systems at high end dealers to reproduce this disc anything close to realistically. In fact it is widely reported on the net the disc is poorly engineered. I can assure you it is not, it is a tour de force. there are just few systems on the planet, that can likely reproduce it.

 

[Cpyder]

Is achieving a good Qtc dependent or independent of driver size?

 

[TLS Guy]

Is achieving a good Qtc dependent or independent of driver size?

It is independent.

 

[Erika111]

Of course, this is a pure function of frequency response. One can for example, take a woofer and put it in a very tiny sealed box, effecting a Qtc of 2, and it can then be corrected with electronic line level filters to make it in effect a QTC of 0.7 or any other response target

 

[annunaki]

Of course, this is a pure function of frequency response. One can for example, take a woofer and put it in a very tiny sealed box, effecting a Qtc of 2, and it can then be corrected with electronic line level filters to make it in effect a QTC of 0.7 or any other response target

Very true, but again a set of compromises/requirements comes into play. In doing such said driver must have substantially low power compression, long linear excursion capability, and of course, loads of power on tap. That is assuming one would like the driver usable to the 20hz range.

VERY, VERY FEW drivers fit said requirements. It is definitely not an efficient approach.

 

[audiohonic65]

Thanks Annunaki! Good link to update myself on this gadget. Its better to know the truth then to get confused by the myths. Thanks for clearing my doubts.

 

[WmAx]

Very true, but again a set of compromises/requirements comes into play. In doing such said driver must have substantially low power compression, long linear excursion capability, and of course, loads of power on tap. That is assuming one would like the driver usable to the 20hz range.

VERY, VERY FEW drivers fit said requirements. It is definitely not an efficient approach.

Annunkai makes a great point. VERY FEW drivers are truly suited to the small sealed application. A few suitable examples: JL W7, TC Sounds TC2000(AP REVO), TC3000(AP AXIS), LMS5400( AP ULTRA LMS), R.E. Audio XXX, etc.

The TC Sounds LMS drivers (Sound Splinter has LMS technology drivers made by TC for them, re-badged as SS) are the best drivers for this application at any price to my knowledge; this is based on 3rd party analysis of the actual driver performance in acoustic tests and objective analysis of the motor system. The LMS offers the absolute longest true linear stroke of any known driver and has massive thermal dissipation capabilities.

-Chris

 

[TriMe]

thanks for posting this article - like it.