Group delay in subwoofers


I understand the phenomenon of group delay when subwoofers are connected to a preamp and that they need to be placed approximately 8 ft closer to the listener than the mains.  Is this also the case when connecting a sub through the speaker level inputs from an amplifier or is group delay much less of an issue in this configuration?

jc4659
I would think connection via the speaker terminals should have no issue with delay, but I am not an EE.
Perhaps Almarg will help. If anyone knows about this stuff, it's him.
Bob
Delay is caused by the velocity factor of electricity through the paths it takes. Wire and circuit board traces are generally the fastest parts on the trip, but still you need to take the aggregate length of both routes to know if one is significantly delayed compared to the other. This is easily done with an oscilloscope comparing the output of each path fed by the same input source (i.e. a 1khz sine wave). The best solution is to eliminate the subwoofer altogether and go with speakers that have sufficient bottom end response. 
Um, um, um, it is complicated.

By themselves, a large woofer driver does not have any group delay other than the position of the motor relative to the other motors.

BUT!!

DSP processing like you find in a lot of advanced subs can add up to a couple of milliseconds worth of delay. This affects the slope and phase matching as it hands off to the main speakers. On the other hand, if both your top and low are going through DSP, the difference is negligible.

Best,
E


Thanks for the comments.  I had a feeling that it wasn't quite as simple as I had hoped.

JC: Group delay for subs isn't as important as the proper phase/amplitute matching through the crossover, room acoustics and EQ.

That's where you should focus your time and energy.
Thanks, Erik.  I absolutely agree and would need to buy a processor to do it the right way.
Rythmik Audio subs come with a plate amp that includes a continuously-variable phase control. The control allows time-aligning woofers to speakers without physically moving either. The Rythmik PEQ model plate amps also provide both low level connection (on RCA jacks) and high/speaker level (on binding posts).
For real and detailed information go to soundoctor.com and get ready for some serious reading. Super informative and helpful.
I've read it and unless you have the tools and patience to be fanatical about it then you have to live with compromises which are clearly audible.
Jc4659, I spent the last 4 days dealing with sub setup and group delay. My experience was not to use the setup info from the manufacturer.  Did that and it was a waste of time. I did a lot of research and followed the advice given by soundoctor.com and referenced other sources. The first and very important step is proper placement within the environment.  Once I found the sweet spot I again followed manufacturers instruction and again wasted my time. I then followed the instruction by soundoctor.com and finally hit the nail and I'm now loving it. Enjoyed my fully properly integrated sub tonight from 5 to 7 pm. All the tools required were a tape measure, SPL meter and muscle power. Soundoctor.com information rocked my world.
@gillatgh I have the sound Doctor cd with all the low frequencies and have used the out of phase method to find the null zones.  Unfortunately the best location is unacceptable to my wife.  Like I said, it's all about compromises.  Congrats on dialing it in.  You know when it's right.
For sure compromises are part of the game. The trick is to get it as close as possible to the sweet spot. I was fortunate to find an acceptable sweet spot which also was aesthetically acceptable but it certainly is not dead on but within the zone. The result may not be the best it could be but it's close enough for awesome rendition. My point really was that manufacturer instruction will not get you there while soundoctor.com information was free and very informative. That and their links to relevant info were invaluable to me