Difference between polarity and phase w/sub

The polarity switch inverts the polarity of the woofer 180 degrees, while a phase control might give you continuously variable phase change (my Paradigm allows change from 0 to 180 degrees). To do this simply, with both the satellites and sub playing a recording with a consistant low bass instrument, turn the phase control until you get the most bass. Then you can play with the polarity invert feature to see which position sounds more natural to you. You could also do this with a test disc and a meter as suggested above, but it's probably not necessary. Regardless of the amount of control you have, there is no substitute for proper placement of the woofer in the room... Move it around and leave it where it sounds the best. Sometimes moving the woofer a matter of inches makes for profound audible improvements. I usually position the satellites for best bass first and subsequently position the sub.

This is one of the most misunderstood concepts for the audiophile, perpetuated because manufacturers such as Conrad Johnson and many others use the terms incorrectly. It is also very difficult to explain without pictures of the waveforms.

In a stereo system the signal alternates between being positive and negative, ultimately causing the speaker cone to move back and forth creating sound pressure waves. Polarity refers to whether a signal is positive or negative. Inverting polarity means that what was positive is now negative and vice versa. If the speaker cone was moving out at certain point in time it is now moving in. Swamp is correct that reversing the speaker wires will invert (reverse) polarity.

One problem in understanding this is that many describe this as a phase reversal, which is incorrect. Phase refers to time. If something is out of phase then it is occurring at a time different than the original signal.

Take two identical speakers being fed the identical signal. They are moving in and out in lock step. If I reverse the connections to one speaker, while one is moving in the other is moving out. This is an inversion of the polarity to one speaker, but most people will describe this incorrectly as a phase reversal. They will say that the speakers are out of phase when the correct terminology would be that one speaker has had it's polarity reversed. This terminology is so widely accepted that it is probably impossible to correct.

Take the same two identical speakers being fed the same identical signal but one goes through a slight delay network. They are moving out and in but one lags a little behind the other. They are now out of phase. Your sub has an adjustment to vary the amount of this delay.

When attempting to integrate a sub with the main speakers, you want the positive pressure wave from the sub to coincide with the positive pressure wave from the main speakers at the frequencies that they are both reproducing (around the crossover frequency). Since they are different distances from the listening position, moving in and out at the same time is not enough since the pressure waves have to travel different distances to reach you. By delaying one of the waves (using the 0-180) phase control it may be possible to get these waves to overlap. If the amp to the sub inverts polarity and the main amp does not (or vice versa), then using the polarity inversion switch on the sub will put the polarity correct. You can then use the phase control to fine tune it to make up for the difference in distance.

Thanks for the replies. Thanks Herman for the indebt definition of phase. I knew that inverting polarity means to switch the positive and negative lead, but was not sure about phase.

Herman:

If my sub is located between the main speakers but is about 3 feet behind them, how should I set phase?

Thanks,
prpixel

You adjust the knob until it is in phase with the mains. You will know this because the bass will be strongest at this setting. It can be done by ear but is much easier with a test recording and a sound pressure level meter. Play frequencies near the sub/main crossover frequency and adjust phase for maximum volume.

I had the same questions about phase control on a sub.  Most have them.  With the vast majority this is best put as phase "at 80 hz".  It's implementation is a simple time delay, milliseconds.  For example, 180 degrees reversal is really an "equivalent" done with  time delay such that 80hz is fully out of of phase with the main since the half wavelength in time of 80hz can be defined by time.  Around 32ms.  Set to 90deg and it's really a 16ms delay.  Effectively 90deg at 80 hz but now fully out at 160hz.  The good news is that subs have low pass cutoffs and often slopes to play with.  Personally I'd start at 90deg so that mains to sub handoff isn't boosted with a bloom nor suck-out at most affected/audible overlap area or... 80hz.   Vary from there to match room/sitting position.  The knob exists to control bloom/suck-out.  Setting to "most bass'" may just be bloom or room node.