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Calculating lengths for Marimba Bars - (Qs from Wes Tom)

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-----Original Message-----
From: Wes Tom
Sent: Wed 10/10/2007 1:08 PM
To: jim@percussionclinic.com
Subject: marimba bars
Hi jim,

i want to make a marimba that has 4 bars. middle c d e and a. its a project and i have to play mary had a little lamb. so for each of those bars, how would i know what dimensions to use to figure out how to make a decent middle c sound. i know how to make the resonators, but i don't know how to figure out what kind of dimension is best for those notes. you said that types of wood result in different sounds, but i want to know how to make bars that make those notes. using regular wood

thank u so much
wes


hey its wes again

if it was to confusing to understand wat i wrote. i just want to know how to have the bar fit with the radiator??? like if i calculate the radiator pipes and get it to be middle c, will any wooden bar work?? i know the diatmeters of the radiator and the bar are the same.

wes


Dear Wes - I think I understand what you are asking…… - you are correct that a good balance is usually obtained with the resonator diameter similar to the width of the bar. The dimensions of the bar are actually not that important, as long as it produces the correct frequencies when struck. In a sense any wooden bar will work, but it DOES need to be tuned to the same fundamental frequency of the resonator. The idea is that the bar actually produces the sound, and the resonator simply amplifies the fundamental by resonating sympathetically. A good dimension for middle C would be about 36cm long by 5&1/2 cm wide by 2cm thick. With most timbers this will produce a note that is higher than middle C so the bar must have the arch carved under the middle to lower the pitch. If you want to be more fussy about the tone, then you need to carve the shape very exactly to make sure all the upper harmonics are also in tune, but for most amateur instrument makers, just tuning the fundamental will be enough.

By the way, I should also mention that for "Mary had a little lamb" you will need the notes: C, D, E and G - not C, D, E and A.

Hope this helps!

Jim McCarthy


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thanks but when tuning the bars, do i need to buy a tuning device or can i like use tuning forks and try to determine if its tuned or not?? and if the bar isn't in tune, to tune it, do i just hit the bar differently??

wes


Dear Wes…

Well it all depends on the range of the notes you are trying to pitch and how fussy you are. It is certainly possible to tune notes by ear alone if your ear is good enough, but some of the upper partials may be very difficult for your ear to hear, or separate out from the other notes present. For my bass notes, I used a KORG tuner to assist me. This was possible because even the upper partials were not that high, and the notes were ringing for long enough that the tuner could get a reading. Big bars are also easier to hold so the upper partials are isolated. Low notes usually require some help, because human pitch recognition gets worse with lowering frequency. As the notes go higher, the upper partials will become increasingly short, and out of the human hearing range - at least the easy to hear range. The middle range might be possible by ear alone, but you will have trouble as you go higher - particularly with the upper partials. Most professionals use a stroboscope or software stroboscopic tuner to tune marimba notes. Google Peterson tuners for some info.

Hitting the bar differently will not change the note at all - it might change the tonal characteristic, but this is simply a matter of changing the relative strengths of the partials - the same partials are all still there at the same frequency. The bar is tuned by the precise carving of the arch on the bar's underside.

All the best…
Jim

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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