[Jazz and Baroque]

Many powered subs have a phase adjustment switch/pot.  Most have a switch for 0 or 180 degrees (change polarity).  Others have 0,90,180 and 270 choices.  Some have continuous adjustment.   

I am moving to adding subs to my system and I am trying to think how important this phase adjustment would be.  I expect to put a Marchand crossover after the preamp and then bi-amp the subs and main speakers.  I intend to place the subs physically close to the main speakers, not in the corners. 

I know that the cable length for the subs will be different from the length for the mains, but I don't think that will introduce a huge phase shift.  The different amps probably won't do it either, except for possible inversion.

Is this really an important issue??  Is basic polarity change all I need to check, if the subs are close to the main speakers?? 

Thanks,
Mike

[bpape]

0-180 is the minimal requirement.  If you're out of phase, you can get severe cancellations at the xover frequency. 

A continuous phase adjustment can offer a much finer level of detail to really dial things in.

All of that said, place the subs where they need to be placed and provide the smoothest integration and fewest nulls overall.  This may be close to the speakers, may not be.  That's the advantage of subs.  You put them where bass response is best without messing up the mains setup in terms of imaging and boundary issues.  In this case, a continuous phase adjustment is very very nice to have.

Bryan

[ctviggen]

The cable difference will make no difference to phase shift. Using 1128ft/sec, a 40 Hertz signal has a wavelength of 28 feet.  The half wavelength would be 14 feet, which means that you'd have to move the sub 14 feet away, and if both the speaker and the sub were in phase, there would be complete cancelation at 40 Hz.  An 80 Hertz signal has half that wavelength, or about 14 feet.  A few feet could make a difference.  I'd want at least phase reversal (although you could always simply reverse the phase of your speakers by reversing the speaker cable).  Woops -- can't write more.  Gotta help with the baby.