This mentions a technique called Impulse Response. This actually is a very very usefull technique to determine room acoustics. In fact, I was kind of suprised to see the consumer industry does not use it as much as I would think. In my opinion the impulse response is best used to determine reverberations. From the time between the reverberation and the original pulse you can figure out the distance the sound traveled. From that you can basically look around and try to come up with the path that sound traveled. Usually you will see a significant reverb pulse from the speaker bouncing off the side wall and to the listener/microphone. Depending on the results you can determine which walls are best to acoustically treat. As far as "EQing" this signal out, I dont think it would do much to the impulse. EQing < 250Hz is a valid point, however I still have had good experience with very slight EQs of < 3dB. I have a 15 Graphic EQ which I do very slight manipulations, however I will say most of the time it is in the lower frequencies.
I wish these "low price have every feature available" receivers would just give the user direct access to a parametric EQ.
Standing waves have been around a long time, and the last time I designed a speaker enclosure there was major consideration on the dimensions of the box. You can calculate the standing wave of your room, find a sine wave generator on the computer and put that frequency through your speakers and walk around.
I still believe changing factors of the physical room itself is most important. Obviously most people can't do that, so SLIGHT DSP EQs can sometimes help. You hit auto calibrate on an EQ that trys to compensate for your room - Yuck.
I have been meaning to maybe write up a way I learned to do impulse responses, however it is very complicated and math intensive. A easier way is to do this: Hook up a mic to your computer. Download Goldwave (I think its still free) or a similiar program. Blow up a balloon and pop it. Analyze waveform. Problem is an impulse response is a wave that is infinite amplitude with infinitely small duration. So you need to make the loudest "bang" possible. Using some complicated math you can use a long pulse for 30 seconds or so and mathmatically conver this back to an impulse.
