Subwoofer Tests Round 5, 6th of October 2007, Test Summary ***READ ME***

[ISLAND1000]

SteveCallas wrote:

I think you're taking this a bit too seriously man

Nah . . . . . I'm OK . . . .
What's happened in the months since I assembled my LMS-5400 18" based system is that I realized how smooth and distortion free the upper range of the frequency response is. I've decided that a 120HZ X-over point is reasonable and am now searching for a way to design a two way speaker to go along with the LMS. The problem is to match the spl output and power handling capability of both the LMS and the new two way unit .I could use the two way as mains and/or surrounds.
Anybody here have any real world experience with a 6.5 inch driver that is rated at 150 watts and can do 110 db?

[ISLAND1000]

Ilkka has performed additional measurements labeled under "Miscellaneous Measurements" on several subwoofers and has again supplied food for thought.
The performance enhancements produced by "response shaping electronic controls" contained within the subwoofer units provides additional adjustments usable in differing room sizes and treatments.
The graphs also show that electronic shaping of the response curve is very doable and very accurate. If anyone has lingering doubts about the ability of receivers, amps, BFDs, Room EQs, and parametric equalizers to add performance enhancements to a sound system, they should now rest easy.

[Ilkka]

ISLAND1000 wrote:

Ilkka has performed additional measurements labeled under "Miscellaneous Measurements" on several subwoofers and has again supplied food for thought.
The performance enhancements produced by "response shaping electronic controls" contained within the subwoofer units provides additional adjustments usable in differing room sizes and treatments.
The graphs also show that electronic shaping of the response curve is very doable and very accurate. If anyone has lingering doubts about the ability of receivers, amps, BFDs, Room EQs, and parametric equalizers to add performance enhancements to a sound system, they should now rest easy.

Phil,

I moved your post/thread here. Please do no start new threads because I want to keep the main page as clean as possible so that each subwoofer will be easier to find. Thanks!

[hikejohn]

Interesting stuff, have you ever tested a Wilson Watch Dog 2 sub? or the Revel 30?

John

[Ricci]

I've come across something interesting in Illka's tests. I was running through the DIY subs that were tested and simulating them with WinISD to see how closely the predicted max output matched up with what was the actual real world results that were measured. Most of them are quite close, which was actually a bit of a surprise.

All of the subs had the most deviation from the theoretical down at the lowest freq's 12.5 & 16hz. The 2TC subs... TC2000 and LMS5400 were extremely close to what WinISD predicts. The TC2000 was short a maximum of 2.1db at 12.5hz from predicted in the 270L vented design. The LMS was off a maximum 0.9db from the predicted max output at 16hz in the 100L sealed! Seems like what you simulate is pretty close to what you will get with TC's subs.

The SDX subs on the other hand were way short of the predicted max output in both the dual driver 140L and single driver 100L sealed. They are both really close down to 25hz, and the 100L sub is only -2db off at 20hz. The 100L is 4db short of the predicted output at 16hz and 5.9db short at 12.5hz. The 140L dual driver sub is even further off from the predicted output...it is -6.5db at 20hz, -5.8db at 16hz, and -9.4db at 12.5hz from what is predicted. I wouldn't think anything of this if the 2 TC drivers weren't so close to what is predicted.

Anybody have any thoughts on this? Seems like maybe the SDX really doesn't quite have 30mm of useable xmax? Perhaps the distortion just gets way out of hand even though there may be output left? Maybe the enclosure volume was too small? The 100L performed much better than the dual driver that only had 70L per driver... I'm just guessing here.

[Mike P.]

Interesting find, Josh. When you entered the parameters in WinISD for both subs, did you use the "auto calculate" feature or did you enter the the parameters as stated by the manufacturers?

[Ricci]

I enter them in the order suggested by WinISD and with the autocalulate feature turned on. I understand where you are going with this, but the small differences between the auto calculated params and the mfg'r supplied ones will not cause that big of a difference in a sealed box. Maximum theoretical output for a sealed system on the low end is all about VD, which is not affected by the parameters much at all(excluding SD and xmax of course).

[Ilkka]

Ricci wrote:

I've come across something interesting in Illka's tests. I was running through the DIY subs that were tested and simulating them with WinISD to see how closely the predicted max output matched up with what was the actual real world results that were measured. Most of them are quite close, which was actually a bit of a surprise.

All of the subs had the most deviation from the theoretical down at the lowest freq's 12.5 & 16hz. The 2TC subs... TC2000 and LMS5400 were extremely close to what WinISD predicts. The TC2000 was short a maximum of 2.1db at 12.5hz from predicted in the 270L vented design. The LMS was off a maximum 0.9db from the predicted max output at 16hz in the 100L sealed! Seems like what you simulate is pretty close to what you will get with TC's subs.

The SDX subs on the other hand were way short of the predicted max output in both the dual driver 140L and single driver 100L sealed. They are both really close down to 25hz, and the 100L sub is only -2db off at 20hz. The 100L is 4db short of the predicted output at 16hz and 5.9db short at 12.5hz. The 140L dual driver sub is even further off from the predicted output...it is -6.5db at 20hz, -5.8db at 16hz, and -9.4db at 12.5hz from what is predicted. I wouldn't think anything of this if the 2 TC drivers weren't so close to what is predicted.

Anybody have any thoughts on this? Seems like maybe the SDX really doesn't quite have 30mm of useable xmax? Perhaps the distortion just gets way out of hand even though there may be output left? Maybe the enclosure volume was too small? The 100L performed much better than the dual driver that only had 70L per driver... I'm just guessing here.

Hi Ricci,

You can't really compare the CEA-2010 max output figures with the WinISD "max output figures" because the CEA-2010 numbers are THD limited (please see this PDF for explanation on the CEA-2010 standard) and are using a burst signal instead of simple sine wave approximation of the WinISD. Also the WinISD approximation is only a function of the maximum power handling of the driver (Pe) or the maximum "linear" excursion (Xmax), whichever is reached first at each frequency. In other words it's EXTREMELY simplified approximation which basically doesn't always (ever) add up with the real word tests, even when not using any THD limiting or burst signals. Simulations are only simulations based on small signal T/S values which change a lot with larger input signals. Also basic simulations don't simulate the effects of any non-linearities (power compression etc.)

But when it comes to the SDX15, the CEA-2010 output down low is limited by the high 2nd order distortion component. This means that the compliance (Cms) non-linearity is quite high i.e. the suspension is causing a lot of distortion which limits the CEA-2010 numbers at the low end. The 3rd order harmonic is quite low which tells that the Bl related distortion is low, thanks to the XBL^2 motor.

[Ricci]

Thank you for the explanation Illka. I figured that it was distortion related to the suspension,but I'm no expert.Now I know and knowing is half the battle.

Do you think that the 30mm linear xmax rating for the SDX is a bit optimistic, or would that be unrelated to the distortion issue?

[Ilkka]

Ricci wrote:

Thank you for the explanation Illka. I figured that it was distortion related to the suspension,but I'm no expert.Now I know and knowing is half the battle.

Do you think that the 30mm linear xmax rating for the SDX is a bit optimistic, or would that be unrelated to the distortion issue?

Can't really tell without Klippel or similar measurement, but when one remembers that...

------------------------------
Xmag = Excursion limit due to the magnetic limitations of the driver's motor. Xmag is defined as the displacement at which the BL product has fallen to 70.7% of its value at the cone's rest position.
Xsus = Excursion limit due to the driver's suspension. Xsus is defined as the point at which the compliance of the suspension has decreased to 25% of the value at the cone's rest position.

From these two figures, Xmax is then derived as follows:
Xmax = The shorter of the Xmag and Xsus values, in each direction of cone travel.
-------------------------------

...so linear doesn't usually really mean perfectly linear, so there can be a lot of distortion even when still operating under "linear" range. I wouldn't worry about sub 20 Hz distortion that much though.

[Ricci]

I wasn't really concerned with THD down low too much. I'm more interested in the output. Do you think that the SDX's had much left to give in the 12.5, 16 and 20hz bands, or were they almost out of gas? Isn't the CEA-2010 measurement supposed to be an indicator of when a system is "losing it"?

[Ilkka]

Ricci wrote:

I wasn't really concerned with THD down low too much. I'm more interested in the output. Do you think that the SDX's had much left to give in the 12.5, 16 and 20hz bands, or were they almost out of gas? Isn't the CEA-2010 measurement supposed to be an indicator of when a system is "losing it"?

It's supposed to be an indicator when the distortion becomes audible. If you want to see the maximum level without any distortion limiting, you should at the following graphs:





From those you can see the absolute maximum output level at each frequency before major compression. The signal used is a long sine sweep which is more taxing than the very short burst of the CEA-2010 test. Therefore you will see less max output in the upper range but on the other hand more output down low because the THD isn't limited. The amount of power compression at the low end isn't that bad yet, but usually these kind of drivers won't compress that max until they quickly bottom out or otherwise fail. So I would say there's not much output left beyond that highest curve (at the low end).

[Ricci]

Thanks for the info!

[noah katz]

"The signal used is a long sine sweep"

How long? I'd think there would be danger of cooking the voice coils w/sustained high power.

[Ilkka]

noah katz wrote:

"The signal used is a long sine sweep"

How long? I'd think there would be danger of cooking the voice coils w/sustained high power.

30 seconds per sweep from 100 Hz down to 10 Hz.

Of course there is a risk but out of the ~60 subwoofers I have tested, not a single one has had a fried VC. The trick is to listen to the sound and look at the amount of compression.

[noah katz]

"The trick is to listen to the sound and look at the amount of compression."

Not sure what a hot voice coil sounds like, but compression is definitely a good indicator.

[bjs]

I'm considering the SDX15 and am trying to understand the peak at 40Hz.

CSS claim on their website that a 100 litre box should be maximally flat. And indeed when I input the parameters into Unibox it agrees. However Ilkka's test results show a decided peak of 3 dB at 40 Hz.

So a question for you experts...why would this discrepancy exist and what is it's significance? It seems it would take a MUCH larger box to actually produce a flat response (if indeed it could be done). Add room gain to that curve and I'm not sure it looks particularly good.

[Ilkka]

bjs wrote:

I'm considering the SDX15 and am trying to understand the peak at 40Hz.

CSS claim on their website that a 100 litre box should be maximally flat. And indeed when I input the parameters into Unibox it agrees. However Ilkka's test results show a decided peak of 3 dB at 40 Hz.

So a question for you experts...why would this discrepancy exist and what is it's significance? It seems it would take a MUCH larger box to actually produce a flat response (if indeed it could be done). Add room gain to that curve and I'm not sure it looks particularly good.

The reason is called inductance. If inputted correctly, the Unibox can predict the final response pretty accurately. Usually most simulation programs don't simulate the effect of inductance or simplify the model too much.

100 litre sealed is fine for the SDX15. Room gain will be the unpredictable factor without measurements. In any case I suggest a good EQ which will help to make any subwoofer sound better.

[bjs]

Ilkka wrote:

The reason is called inductance. If inputted correctly, the Unibox can predict the final response pretty accurately...

CSS doesn't list the le2/re2 values...have you (or anyone else with the actual drivers) measured them by any chance? Anything to improve the model correlation is a good thing.

[Ilkka]

bjs wrote:

CSS doesn't list the le2/re2 values...have you (or anyone else with the actual drivers) measured them by any chance? Anything to improve the model correlation is a good thing.

I can measure them for you, just give me few days.

[bjs]

Great Ilkka! Especially since my request to CSS for the info has so far gone unanswered. Thanks.

My (very rough) correlation of the Unibox model with your test results suggests some pretty big numbers (assuming the rest of the published CSS numbers are correct) so I'm interested in what you get.