Subwoofer Tests Explained - Page 3 - Home Theater Forum and Systems - HomeTheaterShack.com

 
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post #21 of 45 Old 07-31-08, 07:23 PM
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Re: Subwoofer Tests Explained

Quote:
noah katz wrote: View Post
The loading at Fb ought not restrict excursion at higher freq, and would have certainly been noticed in ported systems.
It guess its not so much a question of restricting the higher frequency excursion, but adding distortion to it. A case in point can be seen in some of Ilkka's Round 5 results if you compare the % THD plots between the sealed LMS-5400 and the 2xPR LMS-5400. For every SPL level 105db and higher, there is significantly more THD between 35 Hz and 100 Hz for the passive radiator version (even though it has twice the volume).

2xPR LMS-5400:
http://personal.inet.fi/private/zipm...200l%20thd.png

Sealed LMS-5400:
http://personal.inet.fi/private/zipm...100l%20thd.png

-Darrell

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post #22 of 45 Old 07-31-08, 07:32 PM
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Re: Subwoofer Tests Explained

Most interesting; I'm not sure what to think of that.
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post #23 of 45 Old 08-01-08, 12:06 AM
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Re: Subwoofer Tests Explained

1) The output levels between the two subs at each of those sweeps is not equal - the PR'd sub puts out more, longer. EQ the sealed to match the FR and output of the PR'd and you will see distortion rise for the sealed.

2) The PRs probably aren't as linear as the driver itself, so when they begin contributing to output, distortion increases. One of a handful of benefits a port has over a PR.


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post #24 of 45 Old 08-01-08, 11:46 AM
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Re: Subwoofer Tests Explained

Quote:
1) The output levels between the two subs at each of those sweeps is not equal - the PR'd sub puts out more, longer. EQ the sealed to match the FR and output of the PR'd and you will see distortion rise for the sealed.
The 2xPR has more output only from 30 Hz down. Are you saying that if the test were repeated with the sweep restricted to 35-100 Hz, the results for that part of the %THD plot would be different?


Quote:
2) The PRs probably aren't as linear as the driver itself, so when they begin contributing to output, distortion increases. One of a handful of benefits a port has over a PR.
How much are the PRs really moving between 35-100Hz
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post #25 of 45 Old 08-01-08, 01:50 PM
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Re: Subwoofer Tests Explained

"The PRs probably aren't as linear as the driver itself, so when they begin contributing to output, distortion increases."

Disagree; the PR's have no motor nonlinearities, only suspension which is mostly the highly linear air spring.
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post #26 of 45 Old 08-01-08, 06:03 PM
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Re: Subwoofer Tests Explained

Quote:
darrell wrote:
The 2xPR has more output only from 30 Hz down.
That does not appear to be the case. Look at the pink 115db sweep for instance - the PR sub is 1-2db higher from 40-80hz and that increases to 6db higher in the 20-40hz range.

Quote:
noah wrote:
Disagree; the PR's have no motor nonlinearities, only suspension which is mostly the highly linear air spring.
Are the PRs using the same soft parts as the driver?


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post #27 of 45 Old 08-01-08, 06:13 PM
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Re: Subwoofer Tests Explained

I believe so
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post #28 of 45 Old 08-01-08, 06:36 PM
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Re: Subwoofer Tests Explained

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That does not appear to be the case. Look at the pink 115db sweep for instance - the PR sub is 1-2db higher from 40-80hz and that increases to 6db higher in the 20-40hz range..
Even if you use the 118dB %THD curve from the sealed 5400, it has considerably less distortion than the 115dB %THD curve from the 2xPR 5400

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post #29 of 45 Old 08-03-08, 11:37 AM
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Re: Subwoofer Tests Explained

The sealed 118db sweep most closely matches the PR'd 115db sweep in terms of output.

But there is something causing a difference in the distortion profile - I'd still have to say the PRs. If we look at the SVS Ultra 20hz, 15hz, or 10hz tunes vs the sealed version, we see less distortion at higher output levels everywhere above tuning with the ported versions. In my mind this is because the air in a port is more linear than a PR.


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post #30 of 45 Old 08-04-08, 01:07 PM
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Re: Subwoofer Tests Explained

Steve,

I agree about the SPL and %THD plots for the sealed vs 10/15/20 Hz tuned SVS PB-13 results, but they are much closer to one another (for upper frequencies) than the sealed vs PR'd versions of the LMS-5400.

Ilka,

For the next round of testing, would it be possible to perform the spectral contamination test for the sealed and ported (PR'd) versions of the SVS PB-13 and LMS-5400 subs?

Thanks,
Darrell
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