Who knows about low frequency room modes?

[tdamocles]

I've been looking into this room modes stuff and been thinking. If I'm off base here, someone please correct me. I've downloaded a room mode calculator and run a few dimensions. The way it looks, to get a low(~20hz) frequency boost (by way of room), one would need a a room with one dimension at least 25 feet or greater? By what I've read, putting a sub in a corner will excite all room resonances. If one would put a sub in a corner in room(20x18x8) all frequencies above 28hz would be excited making low frequency extension look nill because all other frequencies above 28hz have a large db increase. No matter what you do with moving the sub, the room is not your friend if it is smaller than 25ft( for low extension). I guess using bass traps would lessen the resonances and ultimately an equalizer would fix it.

Any ideas? Please chime in.

[DrWho]

I think you might be understanding room modes incorrectly...they are frequencies at which standing waves will occur and are generally considered bad.

Room gain on the other hand is generally considered a good thing. The smaller the room, the more gain you will have. Basically, the room will add 12dB/octave below the lowest modal frequency. So in your example, room gain would begin at 28Hz and you should expect 12dB of gain at 14Hz, and about 6dB at 20Hz.

[basementjack]

I'll just add in that room nodes exist due to the laws of physics, and that you really can't equalize them out - Bass traps are definately the way to go. Many people have had great results with DIY bass traps on this forum.

[JohnM]

basementjack wrote:

I'll just add in that room nodes exist due to the laws of physics, and that you really can't equalize them out

Yes you can, that's why REW exists. However, the EQ is (broadly speaking) only valid at the point where the response was measured and a region around that point whose size depends on the frequencies of the modes and the physical properties of the space, whereas well executed acoustic treatments can improve the response over a much larger area. At very low frequencies the treatments required may be unfeasibly large, though.

[basementjack]

I stand corrected. Can't argue with the man himself!

(For those who don't know and didn't notice John's member #2, John wrote REW!)