Acoustics 201...


Oct 6, 2000
Santa Clarita, CA USA
I'd been having a lot of trouble getting my mixes to translate well to other systems (a lot of trial and error - mostly error) and I finally did a sine wave plot of my monitor/room. No much as 20db differences at some frequencies (I did three runs and averaged the results).

I moved the monitors around (Tannoy System 8 II), put sand in the monitors stands (BIG difference), got some Auralex, etc., so now the mids and high end are much better (smoother) from about 300hz on up..

However, it seems I have a couple of room modes that are causing some serious low-end problems. Specifically, I get a HUGE dip at around 100hz (12db) and a peak right after that at around 130hz (up about 6db). This makes the low-end sound, uh, rather...funky, at best. Otherwise, I get good response clear down to 40hz.

The 100hz range seems to be a "triple mode" where all three room axes have a corresponding wavelength that matches that frequency - according to a couple of room mode calculaters I tried. I GUESS that there is some serious bass frequency cancellation going on because they're hitting each other out of phase.

So the question seems to be: would adding some bass traps actually help bring up 100hz by absorbing some of the low-frequencies so there is LESS phase cancellation? It seems a bit counter-intuitive to trap MORE bass in order to increase it, but if it really IS phase cancellation, it should work. What do y'all think?

Bear's Gone Fission

Well-Known Member
Jan 4, 2001
Before making more investment in room treatment, I'd suggest arming yourself with the article Wes LaChotte (sp?) wrote for the current Tape Op and, if your chair doesn't roll, you might want one that does. Most of our rooms are too damn small to have smooth response in the bass when the wavelengths are so long, so there are peaks and valleys. The real kicker is that these aren't global issues in most rooms, but localized quirks. The cheap but p.i.t.a. method of coping is to learn where in the room your peaks and dips are and learning to use those listening positions to give you the information you need. I used to roam the room when I did live sound all the time and tweak, kind of a unconcious attempt at the same principles. People thought I had a screw loose but I got good mixes. (Wait, those aren't mutually exclusive . . . ) So to hell with the "sweet spot", it hasn't been your friend, anyhow. And if you really have issues, try single speaker mono and headphones (in mono and stereo) for different perspectives.


Ken Weeks

I just brought home some Auralex LENRD bass traps to try and suck up some low frequency excess in my basement studio. My dealer didn't have the regular LENRDS but he did have the stand-mounted variant, which he was kind enough to sell for the same price - same cubic footage but in 4 foot lengths, 4 per box.

After putting two in the back corners of the room I put the other two on stands and started moving them around. WOW! They make a HUGE difference when you set them up just outside each monitor. They block a lot of the reflections from the side of the room, now the each instruments placement in the stereo field is much clearer.

A real acoustic expert could make the room sound a lot better, but I'm greatly impressed at how improved the playback sounds with these big chunks of foam standing sentry on either side.

The stands also keep the foam out of reach of my cats ("CHLOE! STOP THAT! THAT's DADDY"S $50 foam!!!") :mad: