John Sayers' Recording Studio Design Forum Archive

I have calculated the room modes for my tracking room and determined problematic frequencies, now I am building some resonating bass traps to put above my ceiling. I have read parts of Everest's Master Handbook of Acoustics, but when it comes to instructions on building these resonators, he only specifys the depth (that it should be a quarter wavelenght deep). What I am curious about is the length and width. I have been told that the larger the length and width, the more dB of reduction the resonator will offer. Therefore, my idea is to construct the width of my resonators to be approximately two feet or so, and the length to be the entire length of the room itself. Being that each of these resonators are only about two feet wide or so, and the room is 16.8 x 22.8 x 12, I will be able to add somewhere around 7-8 resonators above the floated ceiling, tuned to specific problematic frequencies. It seems like a good idea to me, but I don't have much practical experience. If anyone has a word of advice, it would be greatly appreciated. Also, I am not sure what the best material would be, though I'm assuming plywood would be fine.

First of all I wouldn't recommend tuned absorbers until you've added enough broadband absorption to smooth out ALL modal dips/peaks - this is better done with broadband methods than tuned ones, especially since all modes terminate in the corners of a room.

With that much ceiling height, you would probably be a lot happier putting cloth covered heavy rigid fiberglass or rockwool between ceiling joists in a 2 foot band around the ceiling perimeter, then covering with (fire retardant) cloth of your choice - stuff as much plain fiberglass batt insulation into the ceiling cavity as you can afford before doing this, and see what the room sounds like. It's very likely you'll only need a few spot treatments for early reflections after this, and the room should sound smoother that way IMO...

As far as panel resonators go, plywood is the material of choice - at their peak they will absorb about .8 or so, which means that for every square foot of surface you would get .8 sabins of absorption at peak frequency. At other frequencies, it falls off pretty rapidly and is hard to predict as far as adding various amounts of inner insulation, where the insulation is mounted in relation to the panel, etc... Steve

Thank you very much, its great to actually get a response. I will definately take your advice and give the tracking room some broadband treatment first. From there I can determine whether or not to invest in more specific types of treatment.