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making an orff style resonator box for xlophone bars

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-----Original Message-----
From: alan smollen
Sent: Tuesday, 12 February 2008 1:50 AM
Subject: making an orff style resonator box for xlophone bars
Dear sir,
I have the bars off and old xylophone and I would like to build a resonator box or 2 or 3 to be able to hear them well for my elementary school.
Do you know the math or where I can get it to give me a guide as to the size and the need or not of separate chambers in the boxes?
I think I could just measure another schools orff instruments and go with it.
I saw your marimba and it is nice. but I think for kids, a box would be better.
If you have any advice I sincerely appreciate it.

Alan Smollen
In Japan

Thanks for your email Alan.

If you have some commercial orff instruments that you can copy I certainly think that would be your best option. I don't have any particular equations to help you out, but with resonating boxes of this type, it is both the height of the "floor" under the bar and also the overall volume of the chamber which counts. Most of the better box instruments have a separate chamber for every 3 or 4 notes. The main issue for your situation is that the length of the bars may not match the dimensions of the box you are copying - in that these instruments are designed such that the nodal points of the bars match up with the width of the box where they sit in position. You will most likely find that the height of each chamber is roughly speaking a bit less than 1/4 of the wavelength of the notes it is amplifying. If you find at the lower end of the instrument that the chamber is not big enough to resonate properly, you may be able to rectify the situation by using some thin plywood to partially close the top of the opening a little. This will lower the resonant frequency.
All the best.

Jim McCarthy

answers by Jim MCCarthy - 12/02/2008

For more help on instrument building you can email Jim.

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