Perhaps Almarg will help. If anyone knows about this stuff, it's him.
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.
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.
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).
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.
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
@bdp24 Can you tell us more about the continuously-variable phase control. I researched a DIY phase control solution (not just a 180 switch) awhile back and couldn’t find anything on it. I actually convinced myself that the continuously-variable dials I see on subs aren’t doing what they say they do. Haha! So... they do exist? How in the heck do they work?
Subwoofer should be close to the plane of the front L and R speakers.
8 feet is likely going to begin to cause some integration issues with main speakers simply because that puts the subwoofer much closer to the listening area (creating uneven sound and making stereo subwoofers a better option)
Group delay is important but this comes from ported subwoofers. DSP is not a significant delay at subwoofer frequencies.
if the subwoofer is sealed then you really don’t need to worry at all
If either your speakers or the subwoofer are ported then you likely will get best results following THX guidelines - sharp cut off filters at 80Hz and therefore minimize speaker and subwoofer overlap. Ports are what usually causes the largest group delays.
Finally your DSP should be able to correct for speaker and subwoofer distances to the listener so that everything is coherent at the listening area.
@mkgus, Rythmik provides very detailed information about phase and loudspeaker/subwoofer integration on the company website (rythmikaudio.com). The Rythmik A370 and H600 lines of plate amps include a "PHASE/DELAY" continuously variable knob control, providing 0 to 180 degrees of adjustment. Put in terms of time, that is zero to 16 milliseconds of delay. As sound travels roughly 1 ft. per millisecond, setting the control at 1ms in effect electronically moves the subwoofer back one foot. The control is not able to move a sub forward in time, of course! If you set the control to 180 degrees, you have just inverted the phase of the sub (which is all a 0/180 phase ’switch" is able to do, greatly limiting a users ability to integrate speaker and sub).
The Rythmik website page on integration explains in very understandable terms (with examples) how sealed versus ported speakers and subs can have their outputs put in phase via the use of the excellent Rythmik controls (which also include an EXTENSION FILTER providing three degrees of damping---low, medium, and high---at three different frequencies---14Hz, 20Hz, and 28 Hz, a CROSSOVER continuously variable from 25Hz to 120Hz, a single band PEQ control with variable bandwidth, frequency---20Hz to 80Hz, and level---+3dB to -12dB controls, a LIMITER on/off switch, and a RUMBLE FILTER).
Even if you choose a sub from a company other than Rythmik, the information provided on the website’s technical pages should assist you in your efforts to integrate any sub with any speaker. Gee, I wonder if I will now get chastised for "pimping" for Rythmik ;-).