Subs & Group Delay

Low-order harmonic distortion is benign. I'm aware of a controlled listening test in which 30% second harmonic distortion was statistically undetectable - so don't go nuts pursuing low harmonic distortion specs.

Group delay typical of a vented woofer system has been shown to be detectable on test tones, but to the best of my knowldege not conclusively so on music program material - thus the "hotly debated" reference in Shadorne's post.

In my opinion the in-room frequency response makes a bigger difference.

Duke
dealer/manufacturer

Hi Duke, you said, "In my opinion the in-room frequency response makes a bigger difference."

How close of a freq response do you think is "needed", for low freq say from 20 to 100hz to sound good? My thought is +- 3db with one to two peaks and nulls up to 5 to 6db will be close enough for good playback, in most rooms.
What are your thoughts on this?

Bob

I'm aware of a controlled listening test in which 30% second harmonic distortion was statistically undetectable

Second harmonic is fairly benign but 3rd harmonic is bad - so it depends on the type of distortion. The other issue is that 1% distortion at the 3rd harmonic of a 20 Hz fundamental will sound nearly equally as loud as the fundamental note itself due to your increased hearing sensitivity at 60 Hz compared to 20Hz (see Equal loudness contours). So in the end, a distorting subwoofer simply populates the bandwidth where your hearing is much more highly sensitive from 60 to 180 Hz with audible response. This is may be quite the opposite of your original intention when buying the sub - which was to augment the bottom octave rather than overwhelm the 60 to 180 Hz range.

Unless you listen almost exclusively to Baroque Organ, I can't imagine much 20hz content. For HT use, where the 'musical' properties of a sub are.....less needed......it may even be a non-starter when listening to 'effects'.
Also, if Crossed-over low enough, that mitigates the effect of 20hz 3rd harmonic. I cross over at between 40/45hz and even my vented HSU produces pretty tight stand up bass. So the amplitude of 3rd/5th harmonic 20hz is pretty well attenuated.

A couple of follow up questions.

1)An SVS 13" Ultra with its ports sealed shows app 5% THD at 20hz at 100db anechoic. In a real world listening room, that's presumably a crushing spl, so could one safely assume distortion is no issue?

2) The same sub stays below 20ms group delay at 20hz. Is there any benefit to looking for a lower # here? Also, is the goal in GD minimizing the value, or matching it to the gd of your main speaker near the x-over point? (Does that question even make sense?)

3)Magfan - how does a low x-over attenuate 3rd order harmonic distortion. I assume that the sub generates this distorted output as a by-product of its response to a 20hz inpu signal. It seems that the x-over point - which attenuates inputs signals - shouldn't affect this - Am I mistaken?

Thanks in advance.

Marty