Posted by John Swensen on September 29, 1999 at 18:48:05:
In Reply to: Re: Help how can I build a tuba mute posted by Jess Peacock on September 29, 1999 at 17:47:33:
Brass instrument mutes are generally considered to act like Helmholtz resonators, so start by finding out about Helmholtz resonators.
The simplest shape for a tuba mute is a truncated cone, so you could figure out what shape to cut your flat material so that it will wrap up to a truncated cone with the correct dimensions (hint: relate the circumference to the diameter at each end, and don't forget to add material so it can overlap for the seam).
For the shape, maybe start with the same taper as your tuba, with a diameter 1/2" to 1" less than the bell at its insertion depth. You probably will need to experiment with the length and insertion depth of the mute to get something that sounds OK and plays sort of in tune.
I have seen successful mutes made with aluminum flashing and a thin plywood end cap, with the seams and edges taped to protect you and the tuba. The thickness of cork strips (model train track bed material may work) near the small end regulate the insertion depth. Aluminum with this thickness can be cut with heavy-duty scissors or metal snips, but the cut edge is treacherously sharp! You may want to experiment with poster board and duct tape, at least until you get close to the shape you want. You can extend the small end of the mute by slipping smaller truncated cones over the end of the mute and taping in place; that may save lots of rework.
You may want to experiment with different small-end treatments: just thin edges, a thin plate with a hole (vary the hole diameter), a thicker plate with a hole, a longer throat (a straight tube in the plate going down towards the large end, maybe wrapping-paper tubes with varying lengths), etc.
If you systematically alter the variables (one dimension at a time), note the change in tone color, and use a tuner to determine which notes are out of tune and by how much for each configuration, your results could be very interesting to this group. If you, also, relate your findings to Helmholtz' theory in a meaningful way, you might just win your science fair.