Subwoofer Tests Round 5, 6th of October 2007, Test Summary ***READ ME*** - Page 6 - Home Theater Forum and Systems - HomeTheaterShack.com

 
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post #51 of 71 Old 01-17-08, 08:25 AM
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Re: Subwoofer Tests Round 5, 6th of October 2007, Test Summary ***READ ME***

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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?
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post #52 of 71 Old 02-01-08, 02:52 PM
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Ilkka's measurements

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.
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post #53 of 71 Old 02-01-08, 09:40 PM Thread Starter
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Re: Ilkka's measurements

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ISLAND1000 wrote: View Post
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!
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post #54 of 71 Old 05-03-08, 09:05 AM
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Re: Subwoofer Tests Round 5, 6th of October 2007, Test Summary ***READ ME***

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

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post #55 of 71 Old 05-05-08, 12:04 PM
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Re: Subwoofer Tests Round 5, 6th of October 2007, Test Summary ***READ ME***

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.
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post #56 of 71 Old 05-05-08, 12:35 PM
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Re: Subwoofer Tests Round 5, 6th of October 2007, Test Summary ***READ ME***

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?




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post #57 of 71 Old 05-05-08, 01:20 PM
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Re: Subwoofer Tests Round 5, 6th of October 2007, Test Summary ***READ ME***

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).
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post #58 of 71 Old 05-17-08, 03:01 PM Thread Starter
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Re: Subwoofer Tests Round 5, 6th of October 2007, Test Summary ***READ ME***

Quote:
Ricci wrote: View Post
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.
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post #59 of 71 Old 05-17-08, 06:27 PM
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Re: Subwoofer Tests Round 5, 6th of October 2007, Test Summary ***READ ME***

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?
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post #60 of 71 Old 05-17-08, 06:42 PM Thread Starter
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Re: Subwoofer Tests Round 5, 6th of October 2007, Test Summary ***READ ME***

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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.
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