subwoofers and panels don't mix

Marty,

Indeed, it is fair to say that the importance of low group delay increases
significantly as you go above 40 Hz. However low distortion remains
important right down to 20Hz because an 80 Hz harmonic of a 20 Hz signal is
likely to be quite loud to your hearing even if it is of the order of a mere 1%.
(This is because hearing sensitivity increases dramatically from 20 to 80 Hz.)

So if you have high group delay and a sub which puts out say 100% THD at 20
Hz then you might be rather concerned about what this is doing to the
unwanted distortion harmonics from non-linearities in the design.

Agreed.

I'm just finding it difficult to reconcile the published numbers I see with what I actually hear. I'll eventually order a pair of SVS 13" Ultras and use them in sealed mode - pretty low distortion from a pair and GD stays below 30 at 20hz. The cost of a pair is still below that of one JL113, so my sense is that this is a good value play. At least as far as upgraded subs can represent good value for me. I guess I'll have a better idea when I get 'em in place.

Marty

Martykl and others - first sorry for not responding in a better amount of time. The research I set out to do was quite time consuming and while I didn't quite finish it I have enough to post. So - first of all I agree with a follow-on comment that group delay is one component of many, completely agreed and good crossover is critical, phase, placement, etc. I'm considering going bi-amping with 3.6s, well let me put it this way, I'm sure I am going to, but its a matter of what year. I really want to do it with 4 Pass 60A.5s, but that costs a car :)... So, the bryston crossover has gone up in cost, I think it used to be 2k and now its 3k, anyway it seems like what you really want to do is crossover from the active crossover, so now I need 2 3k crossovers (I'll probably get them used here), but anyway, agreed on all of that.

To answer a question, I do have some very very cool organ pieces, they aren't my goal, and I agree there is very little information below 35, even 45 Hz overall. But I'm in this to reproduce difficult sounds at the extremes. For far less cost I can not deal with the extremes from what I already have. I want the stuff in the middle and the extremes!!

However, after reading all of this info, group delay seems to make a lot of sense for critical listening of music. And lo me, I have an extra-ported sub when my sub company just came out with not only non-ported subs, but they are designed to be used in pairs, so I could have put one near each Maggie (and some say get three and put one near ceiling, don't know all the details). Anyway, the new Hsu stuff seems perfect for Maggies in some ways.

Oh - someone asked why I care strongly about it going to 20. First, not only do I want it to go to 20, I want it to go to 16! There is information you can feel. Look - there is mid fi, hi fi, and super-hi fi (alright, not a technical term). Similar to what I referred to above about going to extremes. If I already have speakers that do 35 pretty darn flat (although in my non-wall-reinforced setup I rolloff closer to 50), why spend 1 or 2k to go from 35 to 25 when hearing goes to 20 and feeling goes lower? Also on the 16 Hz, I've heard that there are harmonics from the 16hz tones that go up and change the effect. I don't know how exactly all that works.

Okay, but, if the newer 3.6s are 5.5k and the 20.1s are in the 11k range, and I spend 3k on a sub, I'm halfway to 20.1s! If I had 20.1s I would spend less time on sub forums :)... (Of course, given the right actively bi-amped solution).

Okay, so all that said, here is what I gathered:

Martin Logan Depth
http://www.avtalk.co.uk/showthread.php?t=15239
Group Delay
20 HZ 28 ms
25 HZ 30 ms
30 HZ 20 ms

Decent numbers, but very significant roll-off in output from 40 to 20 HZ......

VTF-3 MK3 w/Turbo (very similar to HO w/Turbo, which is what I have, but not as powerful. I would assume as port distance is the same, that the group delay should suffice for comparison.)
http://www.hometheatershack.com/forums/subwoofer-tests/5763-hsu-vtf-3-mk3-turbocharger.html

Group Delay
20 HZ 40 ms
25 HZ 15 ms
30 HZ 12 ms

REL Storm 5 (all I could find for REL)

Group Delay
20 HZ 9 ms
25 HZ 4 ms
30 HZ 2 ms

(So definitely faster that HSU w/turbo - but note not flat at all to 20! Using the Frequency Response Magnitude chart, Peaks at 40, and goes down quite strongly. At 40 it is 92 db, at 30 88 db, at 20 84 db, at 16 81 db. The HSU is within 2 db flat to 16 HZ!.)

JL Fathom - not in my list but many talk about it.

Couldn't hack it flat to 20 HZ, let alone 16!!

But here are its Group Delay numbers anyway:

Group Delay
20 HZ 33 ms
25 HZ 24 ms
30 HZ 10 ms

There was a velodyne SPL-1200 MK2, but it was so fallen off by 20 it didn't interest me, and the group delay was high (60 ms at 20 HZ) so forget it...

Martin Logan Depth

Group Delay
20 HZ 28 ms
25 HZ 30 ms
30 HZ 20 ms

Decent numbers, but very significant roll-off from 40 to 20 HZ......

So my comments on that based on preconceived notions is that I'm very dissapointed in the Martin Logan solution as I would have thought they would have focused more than anyone on Group Delay, I expected bad numbers for Hsu/Turbo models which came through - though not bad as you get away from 20, its really the super low bass that is slow, and REL is indeed king of this issue. I'd like to get this number for the new ULS-15 Hsu, but can't find it. Several people say it is 'low' but no testing and numbers I can find. I really think that might be the one to have.

The only thing with the REL - and maybe just get next model up is it doesn't go as low as it could. People are saying on another forum that 2 ULS-15s are flat to 5 Hz. Woo hoo! Now that is something.

Lightminer,

For your goals, I suspect that a pair of SVS Ultras in sealed (or maybe 16hz tuned) mode would be hard to beat. Remember that the additional sub provides 3db (more like 5db in my room) output, so read the distortion/clean output graphs at lower output to maintain "apples to apples" comparisons.

Also, bear in mind that the output at, say, 50hz from your Maggies will NOT sound the same as the 50hz output from a sub. I can't say for sure which you'll prefer, but I'm confident that you'll hear a difference. If you EQ the subs, I'm nearly 100% sure you'll hear quite a significant difference.

Good Luck

Marty

I know this isn't music, but the movie 'Push' has some of the best bass I've ever heard integrated into a movie. And I mean really low bass. I think flat response is a bit low, raise the level of the woofer (assuming you're crossing over at 60 Hz or below, mine is at 50 Hz), just move it up a tad.

The scene where he walks into the restaurant and moves the salt (water? can't remember) pouring out from the waitress to the person's food/drink with his hand - that should be very audible. If you adjust the woofer up a bit (not too far!) so that you can clearly hear that as loud bass, then the movie will have a ton of really really really really low bass that is well done - not overdone. I'm pretty sure we're talking 20 - 35 Hz bass, that is some serious soundwork they did. If your system doesn't go to 20, you'll be missing out! :)