|Room Acoustics - Research||Room Acoustics - Solutions||Room Acoustics - How it Worked||Room Acoustics - Evaluation||Calculation Table for Different Absorption Coefficients/Sabines|
|Instrument Acoustics- The Problem||Instrument Acoustics - Research||Instrument Acoustics - Solutions||Instrument Acoustics - Practical Designs||Instrument Acoustics - How it Worked||Instrument Acoustics - Evaluation|
Dealing with Acoustic Room Treatment (Part 3)
Our chosen solution was a series of Helmholtz absorbers (see Research section for details of design). The principle behind these is similar to that of a bottle. If you blow across the top of a bottle you will hear that the bottle has a resonant frequency. If you fill the top of that bottle with absorbent material the bandwidth of that resonant frequency is broadened out. The holes in the perforated side of the Helmholtz box act like a series of bottles all very close together.
Sounds hitting this surface are absorbed at the relevant frequencies. The depth of the air gap behind the absorber also plays a part in determining the resonant frequency.
For some reason we did no calculations to determine the resonant frequency of our Helmholtz absorbers. We were supplied with the ready measured and cut pieces of wood. These sizes were probably chosen to accommodate the pre-packed rockwool (our chosen absorbent material) size.
The materials we used were as follows:
First we made the frames and then we added the backs. IT was only after this we realized that it would have made more sense to attach the fronts first. Instead we had to try to fasten the rockwool to the pegboard in such a way that it would not fall off while the pegboard was being nailed to the frame. Some of us did this while others took off their back panels and re did things the sensible way round.
Designs for a number of different types of absorbers can be seen in both the preceding section and in the following pages along with some additional research information on sound traps.
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