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Why long resonators for high notes? - (a question from Wayne Berry)

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-----Original Message-----
From: Wayne Berry
Sent: Monday, 3 May 2004 10:21 AM
Subject: Marimba Resonator Lengths
I have noticed that on the main bars, the resonators get shorter as the notes get higher, as I would expect. But on the sharps and flats bars, the resonators get shorter to about mid-compass, and then start to get longer again. I do not understand the physics of this. Why are the instruments built this way?
Thanks in advance,
Wayne Berry

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Hi Wayne - thanks for your email.

Your question is an easy one to answer. You may notice that not all instruments have the resonators configured this way - there are some that behave as you would expect on both sets of notes. Then again there are some which do even stranger looking shapes on the sharps and flats. Some of the models from "marimba One" and "Malletech" have wavy line shapes and stuff like that. The reason it is always only on the sharps and flats, is because from the audience perspective that's the only set of resonators you can see. The wavy line shape or arch shape is purely for aesthetics (although I don't think it looks any better myself) so there is no point doing it on the naturals, because it can't be seen by the audience.

You are right to be unable to understand the physics of this, because it doesn't make sense until you look more closely at the inside of the resonators. All the tubes are closed off (or plugged if you like) at the bottom end. This creates the acoustic "length" of 1/4 wavelength for each tube. As you would expect - the pipes get shorter as the notes get higher. If you look inside those long resonators under the high pitched "accidental notes" you will see plugs right up high under the bar - in other words the effective pipe is very short as you would expect - the rest of it under the plug could be cut off without effecting the sound at all, but is left on to a "decorative" length. The low notes of course have the plugs right at the end of the pipes.

Hope this makes sense, and answers your question.

Jim McCarthy

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answers by Jim MCCarthy - 06/05/2004

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