Trying to unnderstand phase

glemay

Hey guys,

I'm sitting here trying to understand how PHASE works. My question is why would it matter, when would you have to change the phase on a sub from 0 to 180? Wouldn't the speakers just all be playing the same thing, all firing out and in at the same time? I don't know if I am even on the right track.

Someone please clarify this for me please.

Thanks, Jerry

shack

Same question...Different forum...

http://www.hometheaterforum.com/htforum/showthread.php?s=&threadid=186495

Tour2ma

Started ripping into this thinking, "well that's an easy one." Five minutes later I think I can now take a stab at it.

First there absolute and relative phase. Let's set absolute aside for a moment and only deal with relative. And first let's talk 2 ch then add a sub to the mix.

For relative phase consider the application of positive voltage to the positive terminal of your speakers. This should produce an outward motion of your drivers. Similarly reversing polarity of the signal to the speakers (negative voltage to the positive terminal) will "suck" the driver in.

If both speakers in a 2 ch rig respond the same to the same voltage they are in phase relative to each other. And when you are in the sweetspot on the centerline between the mains, the soundwaves they simultaneously produce in phase will reach your ears in phase and significantly reinforce each other. The result is the sound will be focussed between the speakers creating a nice, realistic soundstage.

Ever wire your mains out of relative phase? The signal is now produced 180 degrees out of phase and in the sweet spot the soundwaves will arrive 180 deg's out of phase. As a result they will significantly cancel each other and create this "spacy" sound that seems to largely float unfocussed around the front soundstage.

The above is nice and simple because on the centerline you are equidistant from the two sources. Now let's add a sub to the mix...

Firstly, the sub is not going to be same distance from your sweetspot as your mains (let's assume you put it further away in a corner). Secondly, the sub is going to be handling some of the same frequencies as your mains.

So if the sub's cone is moving in perfect synchronization with your mains' drivers, i.e., in perfect phase with your mains the soundwave it produces will arrive at your ears shortly after the waves produced by your mains. On a ringing, sustained note the result is you hear the sub as being partially out-of-phase with your mains.

Ideally you want the sub's note to arrive in phase with the mains so sub manf's give you the ability to vary it's phase 0 to 180 deg's to compensate for (in this case) the sub's sound's late arrival...

Whew... Hope that helps...

Frank Z

I don't think so Al.:D

izafar

Given the very narrow freq range a sub is playing(at the lower end of spectrum) the frequencies have a very long wave length. This means that changing the distance/delay of your sub from AVR results in phase shift at the listening position. This is more useful and convineint way of adjusting the sub's phase with respect to main speakers.

Tour2ma

Originally posted by Frank Z
I don't think so Al.:D

Your attempt at humor doesn't phase me one bit, Tim...