Can someone describe for me what the term, "comb filtering" means, as Ethan used it a couple of posts bakc there?
Allow me.
You may have heard of a guitar effect called 'phase shifter' of 'Flanger'. They're similar effects that combine short delays to cause notch filtering. The same thing applies with multiple acoustical paths.
Roughly speaking, any time you mix two of the same signal with one delayed they combine out of phase. The depth of the dips (or in-phase boosts) are determined by the relative loudness of the two. Equal volume at 180' would be your worst-case -full cancellation- (not likely in wall reflections). The frequencies of cancellation (or peaks) begin at the highest frequencies at just a few inches of (acoustic) path difference, and extend down to and include more lower frequencies as the time difference increases.
For an example, in about any untreated room, if you play some steady wide-band signal (mono will highlight this) and walk past across in front of the speakers (or maybe just move your head side to side a few feet) you will hear the effect of your movement changing the combing points.
It's also why they like the phrase; 'Eq doesn't work for this -unless you like to listen with your head in a vise!
Treatment attenuates the alternate paths.
Wayne
