Subs & Group Delay

A couple of follow up questions.

1)An SVS 13" Ultra with its ports sealed shows app 5% THD at 20hz at 100db anechoic. In a real world listening room, that's presumably a crushing spl, so could one safely assume distortion is no issue?

2) The same sub stays below 20ms group delay at 20hz. Is there any benefit to looking for a lower # here? Also, is the goal in GD minimizing the value, or matching it to the gd of your main speaker near the x-over point? (Does that question even make sense?)

3)Magfan - how does a low x-over attenuate 3rd order harmonic distortion. I assume that the sub generates this distorted output as a by-product of its response to a 20hz inpu signal. It seems that the x-over point - which attenuates inputs signals - shouldn't affect this - Am I mistaken?

Thanks in advance.

Marty

Shadorne,

Your point is taken regarding sensitivy vs. frequency - do you miss your "loudness" control?

However, when I run test sweeps on the SMS-1, the lowest audible tones generate a VERY loud rumble at 90db and up. Whatever frequencies we're talking about here (it appears to be app 25hz from the readout), it should be low enough to fall into the "insensitive" range of perception. This doesn't seem consistent with "rustling leaves" and I wonder what the explanation is. I'd also note that A0 on a piano (typically 27.5hz) registers as LOUD! well below the levels implied by your math (the room is not shaking). Any thoughts as to what I'm missing here?

Beyond this, my intended point re:crushing spl is that (it would intuitively seem that) the 100db anechoic test output should register much higher than 100db in a typical listening room. Obviously, there's lots of things going on that affect the change in output at low frequencies between anechoic and real world environments, but my assumption is that the same signal in a 15' x 20' room should be perceived as much louder than in the (quasi) anechoic measurement environment used by HTshack. Do you believe that this is a good assumption (at least below the primary cancellation frequency)?

Finally, do you have a sense as to which test sweep (they go in 5db increments from 90db to 115db) in those subwoofer tests might be the best proxy for LOUD listening - (music) in a real room. Obviously, there are too many variables for a precise answer, but, as a practical matter, there should be a reasonable answer (or range of answers) to that question. Just wondering which sweep you might look to in evaluating a sub.

Thanks in advance.

Marty

Shadorne,

Thanks again.

Your final suggestion goes to the heart of my questions:

1) I'm pretty confident that a pair of 113s will do it right (and look good doing so), but distortion specs are significantly better on the SVS ultra 13 (even with the ports sealed to minimize group delay). Will I hear this?

2) The SVS ofers an appealling 20ms Group Delay, but the JL stays below 10ms (for the most part). Will I hear this?

3) Will I hear improvement IN MY ROOM at MY LISTENING LEVEL with either choice versus my dual SPLR 800s which, honestly, don't seem remotely stressed when listening now.

4)If I spend $2500 for the pair of SVS subs, will I feel less silly than if I spend 3X that on pair of 113s only to find that the answer to #3, above, is "NO!".

5) If I can hear a difference, and the difference is distorion rather than group delay will I still feel silly because the cheaper SVS will get you virtually all of the distortion benefits and most of the group delay benefits at half the cost of the SVS Ultras?

You've been tremendously helpful, but I suspect I'm at the point where tossing it around further becomes pointless. I'll make my decision and report back.

Marty