On tuning Marimba bars - (Discussions with jaro gregorovic)

-----Original Message-----
    From: "jaro gregorovic"
    Sent: 10/09/04 3:30:38 AM
    To: jim@percussionclinic.com
    Subject: Marimba bars replacing

I am percussionist from Slovakia and I am turning to you with few questions about marimba tuning.

I need to replace few bars on my five octaves Concorde marimba and I am trying to make them myself.
I have succeed with low C2 but by doing other two bars I have faced few problems:

1) On D2, I am just right in tune with fundamental tone and 1st overtone (D4) but second overtone (F#5) is already about 50 cents below. Can I correct that? If I would take away material of the bar just before the end of the bar (by drilling from bottom side) will I reduce the difference. What will happen?

2) On E2 my tuner shows that I am already -30 cents with the fundamental but 1st and 2nd overtone are still +10 cent higher than needed. Can I do something with it?

3) And my last question is: How can you explain that well tuned bar taken out of the instrument sounds 10-20 cents lower than when it is above the resonator?

Thank you for your time and good advices.

Sincerely,
Jaro

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Thanks for your email - I'm always happy to help as best I can.

I'll start with the last question first.
I can think of many reasons why a bar would sound higher away from the resonator, but only one reason why it would sound lower. I may be wrong, but I suspect that the resonator is actually tuned a little higher than the bar. Close enough so that the vibrating bar will still activate it, but once you hit the bar the sound from the resonator is stronger, so that's what the ear picks up on. Away from the resonator, you only hear the sound from the bar which is a little lower. Try getting the tuner to listen to the resonator by itself by hitting the closed end with a hardish mallet. That might be revealing.

Your first two questions about bar tuning are really the same thing. The two primary things to understand are: 1. Any timber removed from the area between the strings will make the fundamental and ALL the harmonics lower. You can however to a certain degree, control which note is effected more by exactly whereabouts you take the timber from - more on that later. 2. Any timber removed from the area outside the strings will make the fundamental and ALL the harmonics higher. In this case its pretty hard to control any ratio of which notes are effected more.

Both of your problem bars include partials that are too low, so your only option is to remove timber from the end of the bar. You don't actually want to make the bar shorter because this would make the string holes incorrect. You could use a drill, but the more useful method is to cut a little triangle shape from the end of the bar (in cross-section)

Cross section of bar:

___________________________________
                                  /
---------------------------------    cut away bit.

Once all the partials are well above where they need to be, you use your knowledge of where to remove timber from between the strings to lower the appropriate partial more. In general when tuning a bar - the idea is to get the partials in the correct relative positions as early as possible then carefully work to lower them all together.

So which area effects which partial?
Well in general, the closer to a partial's node timber is removed, the less it is lowered. The closer to its antinode, the more it is lowered.

Cross section of bar:
(!=string holes)

____________________________________________________
         !                               !
         1               2               1
         3       4       3       4       3
         5    6    5     6     5    6    5

1= fundamental's nodes
2= fundamental's antinodes
3= 1st harmonic's nodes
4= 1st harmonic's antinodes
5= 2nd harmonic's nodes
6= 2nd harmonic's antinodes

A bit of intelligent application should see you being able to lower one partial while having minimal effect on the others.

Hope this helps.

Jim McCarthy

For more help on instrument building you can email Jim.

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