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Sub Phase Correction Use

dweezil

pfm Member
Hi All, just been setting up some subs and I've got an irritating question at the back of my brain.
If the wiring is correct and the sub drivers are in a similar plane to the main stereo pair why would we ever need a phase control?
I felt that if I had to use it I would only be delaying the sub signal so could be up to a wavelength behind at test frequency.
This might not matter for a continuous wave but what about a soliton, a drumbeat or the pluck of a string?
Luckily my phasing was correct at zero degrees but I keep wondering and would have probably reversed the connections on my mains if i'd found the need to go to anywhere near 180 degrees.
 
The phase setting is really just a delay. It's not about phase per se (it equates to phase only at one particular frequency). Reversing the polarity of the mains could be problematic - it's not a delay as such.

As you wrote, often you ideally want to delay the mains, not the sub. I think for this you'd need a DSP crossover or AV Receiver.
 
Thanks, that really confirms what I felt. By putting the subs in the right place i'm avoiding phase problems and miniscule timing variations.
It thus sounded right at 60 and 20Hz.
I've got dsp in the preamp and the subs.
A lot of my confusion was in trying to understand the difference in this context between phase and delay; knowing there is none makes it all clear!
 
It thus sounded right at 60 and 20Hz.

Not sure if I'm miss-interpreting what you're saying here dweezil, but a 20hz sound wave is going to be some 30ms behind a 60hz sound wave, so if you're crossing at 60hz, what happens at 20hz is kind of irrelevant.

Might be telling grandmother how to suck eggs here, but you should just be concerned about aligning phase where the sub and mains produce the same frequencies. You want the drivers to re-inforce each other and not cancel each other out at those overlapping frequencies thus ensuring the subs drivers are firmly coupled to the main speakers mid or mid/bass drivers.

Not sure how you are determining if you have aligned phase successfully, but I found the easiest way to do this is to use an SPL meter or SPL phone app and adjust phase on the sub then measure SPL across the crossover freq range at the listening position (identical spot) until you maximise SPL. Better still use REW to measure mains and subs independently, adjusting phase until the phase plots overlap at the crossover. You mention having DSP, are you able to bypass your sub's controls, define crossovers and adjust delays on both mains and sub using that instead?
 


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