I tried doing a search on this, but failed. I'm sure this is the archives someplace, but I couldn't find it. Sorry if this has been addressed previously.

I recently purchased a second subwoofer, and placed it between my center channel speaker and R/F speaker, next to my existing sub. After some preliminary adjustment for levels, I checked my frequency response, and found that I have a horrible null starting between 40 and 45 Hz all the way up to 60 Hz. Its better than 10 db down, really closer to 15.

If I move my subs into the corner, I know it will reinforce certain frequencies (and possibly get "boomy").

Is there a general guideline as to which frequencies are most likely to get the room gain, or is entirely room size/shape dependant?

I get plenty of low bass (25Hz and below), but some of the concerts on DVD and CD's that I listen to sound like the bass guitar and kick drums are missing, due to the decrease at those frequencies. :(

play with the phase of your subwoofers. you could be cancelling each of them out at their crossover area.

John,

> I checked my frequency response, and found that I have a horrible null starting between 40 and 45 Hz all the way up to 60 Hz. Its better than 10 db down, really closer to 15. <

Don't feel bad. All untreated rooms have horrible peaks and nulls throughout the entire bass range. If you measure at a higher resolution (1 Hz intervals) I'm pretty sure you'll find that those nulls are really closer to 30 dB.

> Is there a general guideline as to which frequencies are most likely to get the room gain, or is entirely room size/shape dependant? <

The response at any given cubic inch in a room is the sum of the direct sound from the loudspeakers plus many competing reflections arriving at different times. The different arrival times create the peaks and nulls. Some of the peaks and nulls are due to the room dimensions, and some are positional. That is, when positional the frequencies are related to the distance between the speakers and each boundary and also the distance between your ears and each boundary.

--Ethan

Try separating the subs more; for example, try putting them between FL/C and FR/C. Moving them around will change how they reinforce each other, and where and what nulls you're seeing at the listening position.

You will probably have a room mode for each length of the room (width, length, height) unless something else is affecting that frequency. Things get more complicated from there. http://www.mcsquared.com/metricmodes.htm (in meters)

You can try placing your sub at your listening position and then measure spots around the room. Once you've found a semi-flat response, place the subs there and you'll have that flat response at your listening position.