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In Reply to: RE: Isn't the amp or reciever's THD more important? posted by b.l.zeebub on September 06, 2016 at 03:03:32
Here is one compendium:
http://www.data-bass.com/systems
And another:
http://www.hometheatershack.com/forums/subwoofer-tests-archived/
Unfortunately, a lot of the more recent tests start at 105 dB and go up to 115 or even 120 dB. So the distortion they're measuring is almost entirely dynamic compression. I don't think that's very useful since most people will never play them that loud.
I look more at the 90 dB and 95 dB results (where I can find them) since that's about the loudest I play them. At 95 dB, there are a lot of subs that can hit 20 Hz at 10% THD or less, even some sealed 12 inchers. Some of the biggest subs are at 2-3% THD at 20 Hz and 95 dB.
Follow Ups:
Take a look at the sidebar on "page 90" of the Polk SDA-SRS review linked-to. Julian Hirsh reports "we have never measured a low-bass distortion level as low as that of the [Polk] SDA-SRS."
Specs are 0.7% THD from 70 to below 20 hz except for a rise to about 2% that was traced to a measurement anomoly ("hum picked up by the system") The THD was primarily second-harmonic.
This seems...spectacular...compared to the ~10% THD of the subwoofers mentioned.
Now, being a vented (passive-radiator) box, of course the bass became increasingly out-of-phase below 53 hz; and I wouldn't place any bets on how, exactly, the THD measurements were taken. At 2.5 volts--supposedly 90 dB in the midrange--the bass output seems shy on volume. I have the sense that the article was written to appear all scientific and thorough, while in fact presenting "best-case" info. But I've been wrong before.
0.7% THD at 20 Hz is extremely low, even at 90 dB. Almost seems too good to be true.
The big Funk Audio subs might be able to equal that. Unfortunately, the distortion measurements made on the FW18 and FW21 started at 110 dB. The FW21 stays under 1% THD through the middle and upper bass at 110 dB, and it has a relatively slow rise in distortion at lower frequencies. So it's conceivable that it could remain flat at 1% or less down to 20 Hz if tested at 90 dB. Nothing else I've seen comes close. You're doing well if your sub can stay under 2-3% THD at 90-95 dB over most of it's range above 30 Hz. And all but the biggest subs show a sharp rise in distortion below 30 Hz.
Cheers!
Thanks for those, quite interesting.
Seems ported subs are on average quite a bit better than sealed when it comes to distortion.
If I remember correctly drivers start to produce more 3rd order once they run out of linear excursion so that would be something to look for.
I was hoping to find some incarnation of my woofers but no luck so far.
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