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Making the Resonators
This method of making resonators for the marimba bars comes from Jon Madin's book, Make Your Own Marimbas, which I highly recommend. The ideas here are Madin's, not ours, but we made slight modifications, because some of the materials called for were not available to us here in the US.
For this bass marimba, each bar has a pipe resonator of a corresponding length. The resonators are hung under the bars in two sets; the lowest five pipes are one module, and the highest ten pipes are the other module. (See pictures.)
THE PIPES are made out of PVC pipe, available at Menards, Home Depot, Builder's Square, Handy Andy, and other home construction stores. The measurements in the book for the pipe diameter were 100 mm (about 4 inches) for the lower module, and 90 mm (3.5 inch - this didn't exist in the US, so we used 3 inch) for the higher module. Most of these stores carry Schedule 40 (thick-walled) PVC pipe, which is heavy. Schedule 20 pipe has thinner walls, and is lighter. This was important to me, since I knew that I would be having kids moving the marimba around. So we decided to go with Schedule 20. (This also meant I had to get different caps to seal the ends, because the tube was slightly thinner.) However, most stores only carry Schedule 20 PVC in the 4-inch diameter pipe, and for the smaller module, I needed 3-inch diameter. So I called a friend who was a contractor, and he ordered some Schedule 20 PVC for me from a plumbing supply store. The stuff is available, but sometimes you have to be a bit sneaky to get it.
TUNING. The resonator pipes, like the bars, have to be tuned. But the pipes are tuned to A=443, not A=440! This can be done using a chromatic tuner. The reason it's tuned to 443 and not 440 is that the tiny bit of space above the end of the resonator pipe and below the bar adds to the resonating length of the air column, and lowers the pitch just slightly; so the pipes are tuned high to compensate. See Make Your Own Marimbas for tuning techniques.
When we first bought supplies to build the resonators, we realized that the plans called for a 180 degree U-turn joint for the lowest five pipes. We looked at our local stores - we could get 90 or 45 degree pipes, but not 180 degrees. We finally found some at a plumbing supply store, for $35.00 each!! And we needed five of them? No, thank you! So we realized that we had some angle faking to do.
At first we thought we'd just use two 90 degree joints, like the bass I'd seen in Seattle had. But we realized that the pipes would be heavier on one side than on the other, and the whole module would hang slightly askew. So what we ended up with was a pipe that looked like an upside down question mark. (See pictures below) This balanced out the weight, so that the pipes hung straight down. Then we screwed the cross brace into each pipe to keep them at the right relative distance, and we had modules! (A side note: now, six months later, the tubes are rattling at the screws to the cross braces. The schedule 20 plastic is so thin that the thread is stripped. We have come to the conclusion that bolts with locking nuts would hold the pipes in place more securely than screws in our marimba, since we used schedule 20 PVC. This would prevent the wooden cross braces from coming away from the tubes. We may also put in some rubber washers or felt to prevent undesired buzzes.)
RESONATOR MOUNTS. The resonator mounts are actually a part of the frame which supports the hanging pipes. The mounts are described in the frame section. We faced another interesting dilemma with the supports. Since we had done most of the frame before we had made the resonators, the nails and screw eyes were already in place; but they were slightly off, as were our inner frame dimensions, with the result that the resonators did not hang directly under their bars. We were about a half inch off to the right. We fixed this by altering the resonators module supports on the frame (see the frame section).
BUZZERS. One fabulous feature of this marimba is that the resonators can be fitted with buzzers. Make Your Own Marimbas uses plastic film containers and grocery sack plastic to create a fabulous, kazoo-like buzz that rings as long as the note itself rings. (see above for pictures of buzzers.) The buzz is done by drilling a hole in the end of the film container, and a hole in the resonator tube; then a piece of the plastic grocery sack is stuffed into the hole, held taut by the film container. This turns the resonator tube into a giant kazoo. If no buzz is desired, the lid of the film container is put on.
Marimba with buzzers on.
We actually found a different way to block the holes for zero buzz, since our holes were not perfectly round. We went to American Science and Surplus and bought several #7 rubber stoppers, like you would see in a science lab. They blocked our irregular holes better, because they were rubber and they gave a little around the edges. We attached them with eyelets and string to the resonator cross braces, so they wouldn't get lost if they fell off.
click here for sound clips of marimba with and without buzzers
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