There's a boom in my room

how to improve room acoustics @ 260hz

I record a lot of nylon strung guitar in a small room and I have to EQ-out a certain amount of ‘boominess’ around the 260hz range ie the room resonating with the guitar.

As I understand it, mattresses and curtains etc are good for absorbing high frequencies and Bubbagumps bass traps presumably are good for the sub 150 range?

Any ideas on some cheap solutions for improving things, for someone who has VERY limited DIY skills :D

Hermoltz resonator comes to mind. also known as a slat resonator.

These can be built pretty easily, and there is a formula for what freq it’s going to target.

Otherwise, you may have to trial and error, picking materials in different density, thickness, covering, and distance from wall, and placement.

I’d read up on slat resonators, and look into building one of those, though I’ve been DIY for a while. They seem pretty simple though, just a frame of some sort, inulation in the inside, then slats across the front. THe distance between slats, and width of the slats is what ‘tunes’ the resonator.

hth, good luck

here’s a helpful page:

http://www.saecollege.de/referen…ies.htm

Bookcases, both wall unit and free standing types, can be an inexpensive way to get some broadband absorption. I don’t know if it would attenuate the specific frequencies you’re after or not. But might be worth a try.

I’ve put a little wavelength utility up on http://downloads.phootoons.com. There’s a slider at the top or you can type in frequencies on the left.

To dampen around frequencies hang something acoustically absorbent at 1/4 of the wavelength from the wall or ceiling. To put a broadband dip around 260 hz, make something similar to Bubbagump’s bass trap and put it about a foot away from the wall (in the direction that matches where the resonance is coming from — that’s not a good way to say it), leaving the space behind it open. It’s not perfect but it helps.

Think about what’s already absorbent in the room. It’s possible that frequencies above and or below 260 are getting absorbed and that will only make things worse. Putting absorbent material directly on a wall will absorb just frequencies related to the depth of the material for the most part - mostly hight frequencies.

Also, the wavelength utility can be used as a ballpark resonant finder, though in the real world it’s pretty close to useless for finding where the resonances are. What I do is enter the frequency that seems like and offender in the N*4 box, hit TAB to get it to be calculated, then look at the wave lengths and frequencies that result. They will be for harmonics and peaks and dips related to that frequency. Compare the wavelengths to the room dimensions (don’t forget ceiling height). Trouble spots are possible for wavelengths that match two or more room dimensions. Actually, I usually move the slider until the full wavelength of N is the same as the length of the room, then look at where everything else ends up. Does the width or the height show up? Is so there’s a potential trouble frequency.

As I said this is VERY ballpark. ANYTHING in the room changes what actually happens. And, it’s VERY broadband.

Adding a heavy drape about 1 foot from the wall will provide some absorbtion at 260 Hz. You shouldn’t need to cover all the walls but it may be good to have some on at least one wall in each of the two pairs of opposing walls (assuming a rectangular room).

Absorbtive material is most effective when it is positioned 1/4 wavelength from the surface producing the reflections responsible for the standing wave. This is the point of maximum particle-velocity in the reflected wave and since absorbtive materials (any sort of fibrous material) work by converting the motion of air molecules into heat, it is necessary to place the material where there is motion. At a reflecting surface the particle-velocity is zero, (as it is at multiples of half-wavelength points) and absorbtive materials are ineffective. This is why thin absorbtive materials such as Sonex (2-3" thick) are ineffective at low frequencies.

Panel absorbers work on a different principle (allowing the boundary to flex and absorbing energy in the process) and will provide absorbtion in less space. They tend to be tuned more narrowly however and are generally less effective than fibrous materials (or foam) if you have the space available.

Tube-traps are also pretty narrow in their absorbtion spectrum and were also designed to achieve absorbtion without occupying too much space.

For good broadband absorbtion Real Traps look pretty good. Bubba posted instructions for similar absorbers recently on this thread which should be cheaper and almost as effective.

Good Luck,
Jim

Thanks for your help guys.

Check this out. $39 for a case (or is it a bail?) of mineral wool.

The fibreglass pipes, if you can get them in a larger diameter, are good to put upright in corners iirc.

This is my absorber thread/article - http://www.audiominds.com/acoustics-willy.mhtml but for whatever reason it doesn’t display properly in netscape (or in my version of IE either).

Apparantly the tubes are not very effective below 100Hz.

Even if you have a nice large 12 inch diameter stuffed with stuff?

This is only second hand knowledge. From Ethan Winer’s page:



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I should mention another popular type of absorber, the tube trap, which is available commercially and also as do-it-yourself plans on various web sites. Although these are often referred to as “bass traps,” even the largest tube models are not very effective below about 100 Hz, and the smaller ones become ineffective much higher than that. Marketing hype aside, the real absorption mechanism in a tube trap is simply the rigid fiberglass inside. The reason a 20-inch tube trap works at all down to 100 Hz is that the tube’s diameter serves to space some of the fiberglass away from the nearest boundary, which helps extend its absorption to a lower frequency. But a tube design is no more effective than using plain rigid fiberglass spaced similarly.


Link to the full article