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pargon 4th January 2010 01:52 PM

Group Delay
 
I am in the process of analyzing which of several LF drivers from the collection would be best in a Pass version of EL Pipe-o. Using WinISD the driver with the best extension of bass response also demonstrates the highest degree of group delay around 30Hz. How critical is this? Should a group delay number of 22ms around 30Hz disqualify this woofer? I can tune the box volume to minimize the group delay, but the low frequency gain drops accordingly. Advice around the web seems to be that increased "stuffing" of the tube will help. Thanks in advance for your advice.

WithTarragon 4th January 2010 04:10 PM

Well, we do not have enough information yet.
1. The estimate of 22 ms seems large, are you confident about that?
2. You should be more worried about the group delay around the crossover point.
3. What is the crossover point and how steeply is it crossed over?
4. What are the kind of cabinet are the main woofers in (sealed, vented, horn loaded, etc).
5. Is the proposed crossover going to be active or passive.

Iain McNeill 4th January 2010 04:26 PM

The group delay is a function of the driver resonant frequency and Q and the enclosure. If you want low group delay then you need to use a sealed box and a low Q (e.g. 0.5-0.7).

The El pipe-o is a transmission line speaker, open at the far end so I would guess that this rolls off at 24dB/octave and hence has higher group delay than an equivalent sealed design but others may have better info.

pargon 4th January 2010 07:53 PM

Thanks for the response Herb man
 
#1 That's what the WinISD lists for the driver, in the recommended size box.
#2,3,5 Current plan is to use a passive line level xover from Marchand, in the 40Hz region, where the group delay is about 9ms, but with a very steep curve up as freq goes down to 30 and then back down
# 4 Bass reflex cab on 604's
Thanks for your interest and time,
David

Ron E 5th January 2010 04:44 PM

one period at 30Hz is 33msec. 20msec, being less than a period or two, means no problem. Group delay is a much misunderstood concept that isn't very useful, for the most part.

head_unit 29th January 2010 07:37 PM

If I understand correctly, you are extending the lows by making the enclosure kinda more resonant down there. More resonant = more group delay. But if it's just at very low frequencies, not a big worry.


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