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Using wooden rectangular resonators (Qs leighmorgan)

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-----Original Message-----
From: leighmorgan
Sent: Tuesday, 6 September 2005 1:59 PM
To: jim@percussionclinic.com
Subject: Marimba resonators.
Jim,
My name is Leigh Morgan.
I am a sculptor and am currently wourking on a fully carved base (stand) for a marimba. I have a "Sonor GX10 Miesterklass" bass marimba - the notes (C to A - just over 1 1/2 octaves) sitting in its original Sonor squat timber (plywood) resonator box. This box is not chomatic - Sonor sells a seperate resonator box for the sharps and flats.

What I would like to know is do I have any chance of getting a good sound (using the Sonor tone bars) and making my own rectangular resonators 48mm wide inside (the bars are 45mm wide) The material for the resonators is from Australian Red Cedar planks finnished to 8mm thick.

For example - the low C Resonator would be 48mm wide x 240mm long x 660mm (1/4 wave length) deep. Will this have any chance of giving a strong fundamental?

Note I could use aluminium tube resonators but as the max diameter I can fit under the Sonor tone bars is 50mm and the max lenght is about 900mm (Artistically bet tubes are OUT))

Hoping you can help,
Leigh Morgan

PS. attached is a recent work of mine.


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That harp is really beautiful - I'd love to see a photo of your marimba when its finished.
In answer to your question - yes, you should be able to get a very good sound from a retangular resonator like the one you are planning. One factor is to make sure it is absolutely sealed - ie airtight (except for the top of course) If the insides of the box are relatively smooth it will help as well, so sanding and perhaps a coat of estapol or whatever before its put together, providing of course its artistically ok with you to have a synthetic coating (only on the inside of course) You might have to do a bit of calculation for the end correction. It is usually calculated as 0.61r where r is the radius of the circular cross section - just express this as area and you can recalculate for your rectangular cross section. Particularly for notes this low, I would really recommend some sort of adjustment mechanism to slightly adjust the length of the resonator. With these larger volumes of air, temperature and humidity can make the difference between spot on and no resonance whatsoever. Many use a kind of plunger at the bottom of the tube, but I think this is acoustically the worst place for a sloppy seal - some sort of sliding extension at the top might be better - as long as it can be done so as not do diretly controll the distance from the mouth to the bar.

Hope this helps.
Jim McCarthy

Jim Reccomends www.makeamarimba.com for comprehensive blueprints and building guides to make your own marimbas.

answers by Jim MCCarthy - 01/12/2005

For more help on instrument building you can email Jim.

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