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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
mkgus's avatar
mkgus
82 posts
 
@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?
shadorne's avatar
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shadorne
7,333 posts
 
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.
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bdp24
4,908 posts
 

@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 ;-).

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