Subwoofer Tests Round 5, 6th of October 2007, Test Summary ***READ ME*** - Page 7 - Home Theater Forum and Systems - HomeTheaterShack.com

 
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post #61 of 71 Old 05-17-08, 10:12 PM
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Re: Subwoofer Tests Round 5, 6th of October 2007, Test Summary ***READ ME***

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"?
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post #62 of 71 Old 05-18-08, 07:52 AM Thread Starter
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Re: Subwoofer Tests Round 5, 6th of October 2007, Test Summary ***READ ME***

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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).
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post #63 of 71 Old 05-18-08, 12:55 PM
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Re: Subwoofer Tests Round 5, 6th of October 2007, Test Summary ***READ ME***

Thanks for the info!
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post #64 of 71 Old 05-18-08, 01:55 PM
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Re: Subwoofer Tests Round 5, 6th of October 2007, Test Summary ***READ ME***

"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.
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post #65 of 71 Old 05-18-08, 02:04 PM Thread Starter
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Re: Subwoofer Tests Round 5, 6th of October 2007, Test Summary ***READ ME***

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"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.
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post #66 of 71 Old 05-18-08, 04:20 PM
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Re: Subwoofer Tests Round 5, 6th of October 2007, Test Summary ***READ ME***

"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.
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post #67 of 71 Old 06-26-08, 10:24 PM
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Re: Subwoofer Tests Round 5, 6th of October 2007, Test Summary ***READ ME***

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.
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post #68 of 71 Old 06-27-08, 05:52 PM Thread Starter
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Re: Subwoofer Tests Round 5, 6th of October 2007, Test Summary ***READ ME***

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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.
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post #69 of 71 Old 06-29-08, 11:47 AM
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Re: Subwoofer Tests Round 5, 6th of October 2007, Test Summary ***READ ME***

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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.
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post #70 of 71 Old 07-07-08, 03:58 PM Thread Starter
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Re: Subwoofer Tests Round 5, 6th of October 2007, Test Summary ***READ ME***

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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.
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