Difference between polarity and phase w/sub

In my Anthem AVM20 setup menu there are adjustments for polarity (normal and inverted) and phase (0-180) for the subwoofer output. When I change one or the other it seems to make the same difference. Can anybody give me an explanation of the difference between the two? I have an idea but just want to be sure.

Polarity refers to your speaker connections. + to + and - to - is normal. Phase refers to the inward or outward movement of the diaphragm of the speaker in relationship to the speaker producing the original waveform. For a variety of technical reasons I don't begin to understand, some of the equipment in the recording chain sometimes inverts the phase. Some people say they can hear the difference and so a switch that allows this to be altered in a transducer will give those folks who can hear it, suppossedly more accurate reproduction. Hope that helps.
The phase switch for a sub is used for avoiding bass suck out around the sub's crossover point so that the sub can be better integrated with the main speakers. You will need to play a test CD that contains test tone. Or use the build-in tone generator of the processor if it has one. In either case, play the test tone that is closest to the crossover frequency and adjust the phase switch; whatever position sounds louder is the right setting.

The polarity switch change the phase of the input signal.
I am not familiar with your equipment but have usually found polarity switches to operate in the preamp section to alter the polarity (as described by Swampwalker) for the output of the preamp. Rowland, among others, used to use this to deal with amps or other devices which invert phase. I also don't know why manufacturers produce products that invert phase, but there may be a good reason I am unaware of. Subwoofers often have a phase switch (0= in-phase, 180= out-of-phase). This adjustment is the same reversal of polarity (+ and -) as seen on preamps but used strictly at the subwoofer to integrate with the main speakers as Sidssp outlined. It is no different than if you just switched your cables at the sub. Proper setting for this will be a function of sub placement relative to the main speakers and Sidssp's method is the way to determine what works in your application. You want the two bass sources to be as in phase as possible and this will become evident as the amplitude increases around the crossover point. If you can't hear which setting is louder at that frequency area, use a test CD, and if necessary, a Radio Shack analog DB meter. I recommend the test CD by Rives which compensates for the inaccuracies in the meter and may help you place your woofer for the flattest response in your room. Room placement is extremely critical for subs, despite what some advertisers claim. Random placement and reliance strictly on volume and phase adjustments rarely leads to satisfactory bass integration. I hope this helps.
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.


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

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.