What's Phase Invert?

[UcLaGeE]

I have an Acoustic Research S112PS sub, and there's a Phase Invert button on the back... I'm new to home theater, and the manual says to switch between the two modes and basically hear which one is better... my untrained ears can't tell a difference between either one.... the manual shows a toggle between 0 and 180 deg. but on my sub, it is basically a push in/out button (factory setting was out i think)... but either way, is there a general rule to figure out what i should use (i'm using it with a pioneer VSX-D509S receiver........ Should I even bother with this, or just leave it alone?

Thanks,
Anthony

[audrey]

Sound waves have peaks and troughs just like any other wave. When signals are "in phase" they rise and fall in sync. When signals are "out of phase" one signal rises, while the other falls. These out of phase signals tend to cancel each other out. (btw: this is the principle on which noise canceling head phones work).

To find the correct position play something with low frequency through both the sub and main speakers. Flip the switch. The position which gives the loudest bass is correct.

You can also use a test disc like stereophile's test disc, avia, etc.

[BEC]

Just to add to Audrey's comments:

The idea is to adjust the sub's phase to produce a preferred bass response at your listening location(s). A loud reponse may be what you're after, maybe a smoother/less peaky one. Some locations will be more affected than others, so you may have to move to different locations of the room, perhaps w/a SPL meter and test tones, just to appreciate the effect. You might even find a better listening location.

W/one sub, the effect tends to be fairly subtle. The physical location of the subwoofer (corner, sidewall, etc ...) and listener tend to be stronger effects -probably factors that should be optimized before adjusting the sub's phase.

Good luck. There are some basic articles at eTown.com about sub placement. The last issue of Stereophile Guide to Home Theater had a more detailed look acoustics and speaker/listener position.