sealed vs vented subwoofers

Thanks gents for all of your replies. That helps a great deal. Makes sense. Appreciate it!!

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

Shadorne, I don't go to web sites to compare my subs to others. I listen to them. Have you ever had a pair of RELs in your house or did you dismiss them on the basis of some specification? Those of us who have been in audio a long time have learned that there is no spec sheet or single measurement that will tell you anything definitive about the performance of any component.

Duke,

I am confused now because you say group delay is worse on sealed? You can clearly see on the links I gave how blocking the port reduces group delay - so how do you explain that? (My understanding is that the port radiates one full cycle out of phase at the tuned frequency - inevitably this implies poor group delay at the tuned frequency and can be seen on most plots on HT SHack website)

My guess is that kick drum sounds better on a sealed sub is probably again the higher group delay and possibly port ringing effects. (Port ringing may even affect mid bass quality)

Stan,

I agree with you that measurements are not everything. However I approach things differently from most - I try to start with good measurements to begin with and then listen for what sounds best to my tastes. It kind of weeds out stuff which simply sounds good but is actually adding coloration.

Have you ever had a pair of RELs in your house or did you dismiss them on the basis of some specification?

No. However I did not dismiss them - if you did go to the HT Shack website you will notice they have EXCELLENT extremely low group delay. Lord appears to design these deliberately with a very low Q and therefore they are not as efficient (play as loud with low distortion) as others but are probably much more musical sounding than many of the subs that were tested - especially on a kick drum. I suspect the REL's would work well with low Q speakers like ATC but I have not tried myself - so this is simply speculation based on the measurements. They also use Volt drivers that have a good reputation. I did not dismiss REL.