Shadorne, I disagree with the basic premise of the author of that article. His third sentence describes his foundational belief:
"I soon learned that realistic loudspeaker reproduction requires reproduction of the input waveform, which seems somewhat obvious."
Not all that seems obvious is necessarily correct. The ear does not hear waveforms. Instead, to quote Dr. Earl Geddes:
"You are making a huge assumption here that the ear hears "waveforms". It doesn't. It deconstructs the waveform into a pattern of excitations in the ear (along the Cochlea) which are detected in complex ways."
How then to explain away the consistently-noted subjective superiority of low-Q sealed boxes? Doesn't that prove that good group-delay behavior is the key to natural-sounding bass?
Well, let's take a look into what we know to be audibly significant. Is low frequency group delay audible? The body of published research is inconclusive on the subject. Apparently it is on test tones, but not necessarily on music. But we'll concede that it might make a slight audible difference.
Is there anything else that we know makes a significant audible difference?
Yes - frequency response! We know that the large peaks and dips in the bass region are audible if they are far enough apart to not be smoothed out by the ear's averaging characteristic (which averages and smoothes the much more closely-spaced in-room peak-and-dip patterns at midrange and treble frequencies). We also know that broad, gentle trends in the frequency response are even more likely to be audible than are narrow-band peaks and dips, even though the latter look much worse on paper.
Given that frequency response is known to be highly audible, could the subjective superiority of low-Q sealed boxes be related to frequency response issues? At first glance, that doesn't seem to be the case: A vented box that measures "flat" to 30 Hz sounds boomy, while a low-Q sealed box that is -6 dB at 30 Hz sounds tight and natural. But wait - that's not the whole picture! We are leaving out a very important piece of the puzzle!
And what is that? The room, of course! Typical room gain is +3 dB per octave below 100 Hz. So, our vented box is probably up 5 dB at 30 Hz - no wonder it sounds boomy. On the other hand our low-Q sealed box is -1 dB at 30 Hz, which is much better.
So once we examine bass reproduction taking into account the room's effect on frequency response, the subjective superiority of a slow-rolloff bass system (low-Q sealed box) makes a lot of sense.
But wait - wouldn't the ideal be -3 dB per octave rolloff? How about an ultra-ultra-low Q sealed box? It turns out that the shallowest rolloff you can get from an unequalized sealed box is about 4.5 dB per octave. With equalization, it would be possible to achieve a -3 dB per octave rolloff starting with a more conventional sealed box alignment (assuming adequate excursion capability). But ironically, a unequalized vented box can be designed which comes very close to the theoretical ideal -3 dB per octave rolloff, at least down to system tuning.
Here's a link to a subjective evaluation of a room-complementary-tuned multisub system:
http://www.audiocircle.com/circles/index.php?topic=60103.20 (scroll down to post by ro7939, near the bottom of page 2)
Now I would agree that doing the same thing with large-magnet, large-displacement woofers in room-complementary-equalized sealed boxes would be even better. But, it would cost many times more. When comparing bass systems, there has to be some apples-to-apples basis, or else the biggest and/or most expensive always wins. We must compare approximately equal dollar solutions, or equal size solutions, or equal output-level solutions, or something like that.
So to recap, yes low-Q sealed boxes sound better than most vented boxes, but I believe the reason is that they produce a far more desirable in-room frequency response, rather than their superior group-delay performance making an audibly significant difference. And there are more cost-effective techniques for acheiving a desirable in-room frequency response.
Duke
