Originally Posted by LTD02
eq doesn't really fix a room per se, it fixes a room at a position or an average of a few positions in the room.
multiple bass sources, bass traps, lossy walls, absorptive furniture, even people in the room help stabalize the frequency response around the room.
The fundamental issue is wave interference. It's a spatial pattern formed at low frequences when a signal and a reflected signal combine. The conbination can be "in-phase" resulting in a peak, or "out of phase" resulting in a null. EQ can change the original signal level, but the relationship between signal and reflected wave is what matters, and EQ can't touch it. Acoustic treatments can help, by absorbing energy from the reflected wave. Room construction can help, by allowing more energy to leave the room.
Regardless where the sub sits, it'll excite all frequencies, and the ones that resonate will grow/shrink with position. The first step is some calculations, to find what frequencies will resonate in your size room. I use the excel file from this site.
This analysis shows you 2 different things:
- room mode frequencies
- room mode density
One approach is to make the room large enough that there are a high density of room modes at the lowest expected frequency. That's the approach used in a concert hall. In a residential-size space, this is what limits the problem to bass - upper bass modes are dense enough in small spaces to avoid issues. Mode spacing is adjustable, by careful selection of room dimensions. That's not practical in a finished HT.
That leaves adding absorption at bass frequencies; reducing reflected energy in the room. Ideally, you'd measure the room's reverbration characteristics at low frequencies to ID the main culprits. Then construct and install traps at the problem frequencies of sufficient size to give you the desired response. I can't say if that's broadband corner traps, or tuned Helmholtz traps, to pick two extremes, without the room analysis. ALWAYS define the problem first... to the best of your ability. Without a measurement rig, you can still do calculations... and remember that your ears are the customer, not a microphone!