Axiom Home Page Forums General Discussion Technical Questions Standing waves?

I had to change rooms a little while back and am now stuck with a room that seems to cause some very large drops in output at certain frequencies, most notably between 97hz-113hz and 178hz-183hz (tested using a test tone generator and my ears, no access to an SPL meter right now). These drops (and overall bass response) improve greatly as you get closer to the walls. From what I've read I think I have an issue with standing waves, but havent seen any practical solution to fixing it. Does anyone have any suggestions, or am I just stuck with it?

Diagram of the room:


Moving the sub out of the corner results in a *massive* output reduction across its entire spectrum in the listening area.

There are ways to combat standing waves, such as large and usually un-attractive corner acoustic treatments, along with others. Unless your willing to go that route, which could be expensive, i dont think theres alot you can do.

Hi,

I notice that the two frequencies are almost an octave apart, and given the imprecise nature of your measurement, could have been. Thus, while it could be standing waves, it might also be the room resonance and its first harmonic. The fact that your room looks square (nice drawing BTW) doesn't help, as I'm sure you know.

I'm guessing that you're renting, so can't be damaging the walls, and that you probably don't want to spend a huge amount of money on acoustic treatments, which can get very pricey very fast. I would suggest that you spring for the thirty bucks for Everest's 'Master Handbook of Acoustics'. Despite the formidable title, it's written for normal people, and he teaches you all the physics you need to know. I just got mine, and was very impressed by the thoroughness of his coverage. He even goes into the acoustical properties of carpets, drapes, and people in a listening environment! You might also want to do a web search on 'bass traps' and see what you find. There are several DYI projects that might work for you.

You indicated that pulling the sub out of the corner made a huge difference. How far did you pull it? I've seen test data that indicated, at least for speakers, movements as small as six inches can make measurable effects. You might try to reposition the sub in 6"-1 foot increments, and attempt to get it asymmetrical with the sidewalls and see if this helps. I had a similar problem, moved the sub only about a foot and a half straight out from the front wall, and angled it slightly. I also mass loaded the floor corner nearest the sub with a bunch of old wool blankets I happened to have. Room corners horn load bass, actually everything, and floors are as bad as ceiling, but easier to treat. Everest indicates that cotton is also good. It seemed to help and smooth out the midbass bump I was hearing. At the cost (zero) a worthwhile tweak.

Ooops, just read more carefully and noted that the problem was a drop, not a peak at those frequencies. You're right, most likely standing wave, as room resonance wouldn't do that. Serves me right for trying to think before my morning coffee kicks in. Any peaks noted?

No significant peaks that I could tell. However, I just tried increasing the range of my test tone sweep (35-2000hz this time) and it seems that EVERYTHING below 290hz or so has a reduced output. My sub is crossed over at 100hz, so this isnt a case of inproper calibration unfortunately.

Do you not have access to a Radio Shack? Their 35 buck (US) SPL meter is a gem to use along with test tones. It's very difficult to be accurate by ear.

If I had to guess, your sub might be pumping into a null, though that seems odd in a corner, though I understand that square rooms are subject to all sorts of weirdness.

The Everest book should be your new best friend, before you spend any other money on this- though seeing if small adjustments in the subs position then trying your sweeps would be worth playing with- in a square room, I'd guess that you definately don't want it to be equidistant from both walls.

I am planning to buy a SPL meter, just wating for one of the local Radio Shacks to get some of the analog ones in stock.