I was cranking through Craigsub's hometheaterforum.com thread and ended up at rythmik audio's site. You know how a few clicks leads you into online hypnosis and you wake up thinking "how'd I get here?"
Anyway, they had a pretty good primer on how to tweak subwoofer phase to match your main speakers at the crossover point. Their's involved convoluted math. I looked around to see if anyone had boiled it down to a smpte to follow method.
I did it and it works, so I thought I would share. It's pretty easy. This guide assumes you already have a functioning setup that until now you have been happy with.
1. Set your subwoofer up as you normally would with your AVR. Crossover dial at max and phase angle at 0 degrees. All adjustments are made in your AVRs bass management. No physical dial or position changes are needed.
2. Find a sine wave test tone to play over your system. The tone you need is your subwoofer crossover frequency. ie. 60/80hz commonly. These are available on youtube and good enough quality for what we need. Stream through your system. We want to play both the sub(s) and mains at the same time.
3. Play the test tone at a volume you would normally use your system at and measure the spl output at your listening posistion. (Since it is a pure sine tone it is important to set the mic where your head is usually. This is a good time to see how room modes can entirely cancel or boost sound as you walk around.
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4. Change the AVR distance setting of your subwoofer to shift it's phase to match your mains at the crossover point. This will typically mean increasing the distance to reduce the time lag created by the subwoofer's internal amplifier and filters. As you slowly increase the distance setting watch the spl change compared to your baseline reading. You will eventually reach a point where it will max out and begin to decrease again.
5. Return the distance setting to the point that provides the highest spl output. This will be the point where your subs and mains are in phase at the crossover point. You are done!
In my system this meant changing my sub distance of (real) 13'11" to (virtual) 16'6". This netted an increase of 2db at the crossover point. In an FFT plot it resulted in the reduction of a hump and dip around the crossover point. The outcome was noticably "faster" sounding bass and much less smearing of bass detail in music. Drums and basslines improve. I thought it was good before. Now the subs are seamlessly integrated with the mains
Try it out. It is free and totally works.
