sealed vs vented subwoofers

I believe that the room plays a dominant role in the bass region, and one of the things that rooms tend to do is boost the very deep bass due to boundary reinforcement. A sealed box sub generally gives better synergy with this room-acoustic effect because of its typically higher-but-more-gradual rolloff characteristic. A comparable vented box sub usually goes deeper, but the room's inherent bass-boost often results in excess deep bass energy and a bloated-sounding bass characteristic.

There are exceptions to these generalizations, so I recommend evaluating subs on a case-by-case basis.

Duke
dealer/manufacturer

Shadorne - my bad! You are absolutely right; sealed boxes have LESS group delay than vented boxes. I was thinking that, but carelessly typed the exact opposite.

That first sentence should read:

"A sealed box will have less group delay than a vented box..."

My compliments on your restraint in not calling me the idiot I certainly appeared to be.

Duke

A sealed box will have more group delay than a vented box because it has a 4th order rolloff below system resonance, rather than the approximately 2nd order rolloff of a venteed box. However, the audibility of group delay at low frequencies has not been not firmly established, and recent studies indicate that it is marginal at best with music rather than test tones.

On the other hand, frequency response has been well established to be audible. That's why I focus on the frequency response rather than the group delay or system damping.

The reason for the above two observations lies in the human hearing mechanism. Briefly, at low frequencies the ear is very poor at resolving timing, and much better at resolving intensity.

On another subject, note that the woofer is powered throughout its stroke; it doesn't rely upon the airspring in the cabinet to restore it to rest position.

A relevant comment by Earl Geddes: "Remember that the damping and the frequency response are one and the same thing. If I correct the frequency response then I am simultaneously correcting the damping."

http://www.diyaudio.com/forums/showthread.php?postid=1638754#post1638754

The implication of Earl's statement is that we can focus on the in-room frequency response curve, and when we get it right we have also gotten the system damping right. Focusing on the system damping isn't wrong, as it will theoretically lead to the same result, but in my opinion it's easier to correct the frequency response.

Once while in an exerimental mode I built roughly comparable sealed and vented subwoofer enclosures. The enclosures were the same size and almost the same efficiency. The sealed box used a 10" woofer with a Qtc = .50, and the vented box used a 6.5" woofer and was tuned to give a roughly room-gain-complementary response.

Subjectively, the vented box went deeper and would play louder before audible distortion set in (the latter surprised me). The sealed box had better impact in kickdrum, while the vented box sounded more natural on other bass instruments.

Suspecting that the difference on kickdrum might be related to the larger, more powerful woofer in the sealed box, I switched to an 8" woofer (with a magnet system comparable to the 10" unit) for the vented box. This substantially narrowed the gap on kickdrum but did not eliminate it entirely. By now the two boxes were also approximately the same cost, as the 8" woofer plus vent was close to the same cost as the 10" woofer.

I'm not saying this was a definitive series of tests, and my blind listening panel was pretty small (one person, whose assessments I agreed with). I came away with the conclusion that the cost-no-object approach would be an equalized sealed box with very large-displacement woofers, but that the more cost-effective approach was the low-tuned vented box (which in both cases souned better on everything other than kickdrum).

Duke

For some reason the full link did not appear in my post above. From where that link takes you, scroll down to post number 19.

Duke

Stanwal, I almost agree with your statement about the failure of measurements to correlate with subjective preference. I think it's fair to say that the audio industry has been measuring distortions that are easy to measure instead of measuring distortions that correlate well with human hearing. However, there has been progress made in this area recently which you are probably unaware of.

If you have access to the Audio Engineering Society's library, you might want to take a look at "Auditory Perception of Nonlinear Distortion - Theory" and "Auditory Perception of Nonlinear Distortion", both by Earl Geddes and Lydia Lee. Therein you will find described a rather complex metric that correlates well with subjective perception. The industry has largely ignored it, aside from this article from Audio Express magazine:

http://www.gedlee.com/downloads/THD_.pdf

See also this letter in response to the article:

http://www.gedlee.com/downloads/Comments%20on%20howard.pdf

Duke