Subs & Group Delay

Bob,

The general idea is that low frequencies are much less audible compared to midrange frequencies...with the biggest loss as you go down from 60 to 20 Hz. I may have exaggerated it some but it certainly "significant" whichever way you look at it.

The implication is that harmonic distortion in the 3rd and higher harmonic of a 20 Hz note may be detrimental - even in tiny amounts - making the sound louder than intended on the recording. See what Seigfried Linkwitz has to say - scroll to the bottom of the page.

This is a review of an important AES paper on subwoofers that appeared in Stereophile - The Science of Subwoofing.

Subwoofer

distortion guidelines are offered: Harmonic distortion will not be audible if the second harmonic is below 3%, the third around 1%, and higher harmonics no greater than 0.1–0.3%.

and

The authors sadly report that it is evidently believed in the loudspeaker industry that woofer distortion is not particularly important; as a result, there are very few drivers built that possess adequate linearity. All of this bodes ill for our chances of finding the ideal subwoofer from a commercial vendor.

For details see: Louis D. Fielder & Eric M. Benjamin, "Subwoofer performance for accurate reproduction of music", JAES, Vol. 36, Number 6, pp. 443 (1988).

Most of us are listening to distortion on our subwoofers...

Acoustat6, sorry this reply is late; I've been on the road and haven't logged in since, oh, some time last year.

Anyway, it's hard to say that a given frequency response specification is a guarantee of good sound. It really depends on how it was measured and what the actual data looks like. Consider this aspect of human hearing: The ear tends to integrate peaks and dips over intervals of perhaps 1/3 octave of so (it varies with frequency), so if there are offsetting narrow-band deep dips and sharp peaks close to one another, they might look disastrous to the eye but be completely overlooked by the ear. On the other hand a very broad but shallow (1 or 2 dB) bump or dip is easily overlooked by the eye, but may be quite audible.

An actual in-room response that falls within the numbers you mentioned is probably quite rare, and more likely than not sounds quite good, but it's still possible to have poor sounding bass that falls within those same specs.

Duke