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<blockquote data-quote="envengineer" data-source="post: 2993334" data-attributes="member: 571710">THD always refers to the level of distortion relative to the level of the reproduction of the original signal.&nbsp; It is the sum of the even and odd harmonic distortion values along with intermodulation distortion.So when I said 20%, I meant that many subs produce distortion levels that are 20% as strong as the original signal.&nbsp; npdang has a very good explanation over at DIYMA, far better than my attempt at explaining it.Take a look at the Aura ns12 review here <a href="http://www.diymobileaudio.com/forum/showthread.php?t=11335" target="_blank">http://www.diymobileaudio.com/forum/showthread.php?t=11335</a> and the Atlas vs. TC2 review here <a href="http://www.diymobileaudio.com/forum/showthread.php?t=8" target="_blank">http://www.diymobileaudio.com/forum/showthread.php?t=8</a> .&nbsp; You can see the distortion is quite high. On the distortion analysis plot you can see three distortion figures (BL, suspension, and inductance)The reason nobody really cares is because it is almost inaudible due to the harmonics being so close.&nbsp; At 20 hz you&#039;ve got distortion at 40 hz, 60 hz, etc.&nbsp; and at only 20% of the original volume, the distortion is virtually indistinguishable from the original signal to the human ear.In a tweeter on the other hand, the distortion products are very audible.&nbsp; Say you play a test tone at 5 khz.&nbsp; You&#039;ve got harmonics at 10 khz, 15 khz etc.&nbsp; Those are all very distinguishable.&nbsp; If you want to hear 5 khz, you are definitely going to notice a 15 khz tone being reproduced as a result of distortion, even if it is a relatively low percentage.To help better clarify, take a look at this velodyne link&nbsp; <a href="http://www.velodyne.com/velodyne/tech/faqanswer.aspx?ID=12&amp;amp;sid=316d224n" target="_blank">http://www.velodyne.com/velodyne/tech/faqanswer.aspx?ID=12&amp;amp;sid=316d224n</a>&nbsp;&nbsp; they give a target of 10% as being very good for a subwoofer.&nbsp;&nbsp; I just kind of pulled that link out of my *** by doing a google search but it helps make my point.</blockquote>

[QUOTE="envengineer, post: 2993334, member: 571710"] THD always refers to the level of distortion relative to the level of the reproduction of the original signal. It is the sum of the even and odd harmonic distortion values along with intermodulation distortion. So when I said 20%, I meant that many subs produce distortion levels that are 20% as strong as the original signal. npdang has a very good explanation over at DIYMA, far better than my attempt at explaining it. Take a look at the Aura ns12 review here [URL="http://www.diymobileaudio.com/forum/showthread.php?t=11335"]http://www.diymobileaudio.com/forum/showthread.php?t=11335[/URL] and the Atlas vs. TC2 review here [URL="http://www.diymobileaudio.com/forum/showthread.php?t=8"]http://www.diymobileaudio.com/forum/showthread.php?t=8[/URL] . You can see the distortion is quite high. On the distortion analysis plot you can see three distortion figures (BL, suspension, and inductance) The reason nobody really cares is because it is almost inaudible due to the harmonics being so close. At 20 hz you've got distortion at 40 hz, 60 hz, etc. and at only 20% of the original volume, the distortion is virtually indistinguishable from the original signal to the human ear. In a tweeter on the other hand, the distortion products are very audible. Say you play a test tone at 5 khz. You've got harmonics at 10 khz, 15 khz etc. Those are all very distinguishable. If you want to hear 5 khz, you are definitely going to notice a 15 khz tone being reproduced as a result of distortion, even if it is a relatively low percentage. To help better clarify, take a look at this velodyne link [URL="http://www.velodyne.com/velodyne/tech/faqanswer.aspx?ID=12&sid=316d224n"]http://www.velodyne.com/velodyne/tech/faqanswer.aspx?ID=12&sid=316d224n[/URL] they give a target of 10% as being very good for a subwoofer. I just kind of pulled that link out of my *** by doing a google search but it helps make my point. [/QUOTE]

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