| Helmholtz Resonators |
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or... Where does all that bass come from??? Taken from a posting on the Yahoo Goblet Drumming group and therefore refers to the darbouka and tonbak drums but can also be applied to Djembes and any other goblet-shaped drums In laymans terms, there are two things going on with goblet drums. First, there is a membrane that vibrates (the head) and causes sounds. In doumbek-speak, this would be your "tek" and "ka" sounds. The bulk of the drum does not come into play in determining how these sound, and that's why they still sound ok when you have the drum setting on the floor with the bell (the opening at the end of the drum) covered up. This sound is determined by a number of things, such as the head material, tightness, size and some others that escape my memory at the moment.
The second thing that goblet
drums do is act as a big air spring to cause an air column to vibrate. The bowl
of the drum is a big cavity for air, and the neck/body of the drum forms an air
column. When the head vibrates, it causes the air in the bowl to expand and
contract, In relation to a Tonbak, they usually have very large bowl volumes (compared to an Alexandria style aluminum doumbek) and very small diameter necks or bodies. I would expect them to be very low and very resonant. The doum sound should be relatively independant of the head material, though if the head is too tight it can cause a doum sound to be very short because the air doesn't compress much. If your drum sounds "dead", try loosening the head a bit.
I'm working on a spreadsheet
that will allow you to enter the dimensions of your drum and it will predict the
pitch of the doum sound. So far it is at best an approximation, as it isn't
very
Along these lines, I have a
couple projects I've wanted to work on. One is a drum with a body that can be
adjusted for length and/or diameter (something like a trombone), and one would
be a drum with a body that can have a variable volume. The first one could be
done Ok, enough geek stuff. -Jon | |
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