Tag: Marimba

…How to control humidity

(Every Percussionist Should Know…)
…How humidity can be controlled.

It is humidity not temperature that has the biggest effect on the tuning of wooden note bars. If you ever read so-called “experts” stating the importance of temperature controlled environments with relation to the tuning of xylophones and marimbas, they are talking rubbish. There is a very simple experiment one can do to test the hypothesis; touch a xylophone bar then a glockenspiel note bar; which one is cold? You probably already know the answer – the glockenspiel bar is cold, but why? Glock notes are metal and metal is a conductor whereas wood is an insulator. This is why radiators are made from metal and window frames are made from wood (or should be).

At the extremes, temperature will have an effect on tuning, but that would be an extremely difficult experiment to isolate temperature from humidity. The main cause of atmospheric tuning related problems is humidity. The big word used is hygroscopic in relation to wood, which means that wood absorbs and releases moisture.

A rule of thumb is that hot things like wood and air, can hold more moisture than cold things. If you are that way inclined (and thankfully some people are) you could create a graph to define the maximum amount of moisture something could hold at any given temperature. The graph would depict 100% moisture content. This state is unlikely to happen to your xylophone or marimba, but they will contain a certain amount of moisture in relation its potential maximum, so this is known as relative humidity.

Finally, because wood is surrounded by air and it is hygroscopic, it will absorb or release moisture until it reaches the same relative humidity as the air. The video I made below explains the ramifications of this and what can be done to control it.


Adams Marimba Tuning (Job No: 1069)

A west end show is going on tour and they have a marimba tuning problem; the marimba is tuned to A440Hz, but the musical samples are recorded at A442Hz. So the notes have come to me for re-tuning.
During the first cycle of tuning, I make a record of where the notes are presently, the results are below.

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In the graph, the two smooth lines represent what the tuning should be, and where I need to raise the pitch to. The wiggly lines show that the tuning of the notes is actually all over the place.
The biggest problem area is the third partial which is consistently flat.

In simple terms, to raise the pitch, the note needs to be shortened in length, removing material in the centre of the note increases the flexibility of the bar, which lowers the pitch. It is harder to raise the pitch than to lower it, furthermore, shortening the length affects all the longitudinal harmonics, whereas harmonics can be somewhat targeted when tuning down.

Therefore, I raised the pitch of these notes so that all the harmonics were at, or above the target pitch, then the harmonics that were sharp were brought down into tune.