Percussion Clinic Adelaide

Jim's Marimbas - Page 3

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In the middle of 1997, with the pressure off at long last after many years of full time tertiary study, I discovered that I was getting a little bored, and what's more I still had a nagging feeling that my marimbas had not quite gone as low as they possibly could.

One weekend I came by a huge piece of PVC pipe over 3 metres in length and with an internal diameter of 312mm. I could not resist the challenge. I did a bit of running around until I had found a plastic bucket which just happened to fit perfectly over the end of the pipe, and extend its length to right around that required for a G natural - one step lower than I had gone so far! This seemed just perfect. The length would need some form of adjustment though, so eventually I ordered from a industrial plumbing supply place in Sydney, (can't remember where sorry) a specially made piece of tube 30cm in length that could slide snugly over the outside of the main length. This is essentially a tuning slide for the open end of the pipe.

So "GUS the Gigantic G!" had a resonator around 3.47m long. There was no bar yet, and I know of no meaningful way to fine tune a resonator that depth and size without a bar to activate it, so I left off the resonator and started to tune a bar. For this I used a piece of ordinary Pinus timber 1.47m long and 30cm wide. I could not use a proper type of timber as I simply could not afford it on what was essentially a single note. That amount of timber would ordinarily be enough for a whole small instrument!

I used a power drill and disk sander to do the tuning of the bar. I worked on achieving a fundamental note of 25Hz. The upper partials are in normal ratios - two octaves up then three octaves and a major third. After a whole day of messing around with the sander, a digital tuner, the frequency analysis capabilities of my computer, and all of Bruce's resonators - I finally achieved the completed bar. I had to buy a special long drill bit to drill out the rope holes because that bar is 30cm wide.

I decided to hang the bar vertically. This was for two reasons. Firstly there was no way I was going to get a good, well sealed corner in that pipe. I didn't really want a corner anyway as corners tend to lower the efficiency of a resonator and also makes it difficult to estimate the acoustic length when we are dealing with such a big one. Having the bar almost four metres in the air was out of the question. The second reason for hanging the bar vertically is simply that it allows the bar to vibrate more freely as it is not affected by gravity in the direction of vibration. This is a similar effect to that observed with large concert bass drums. This note is going to need as much energy as it can get from that bar!

25Hz is so close to the absolute limit of human hearing and so low on the hearing curves, that the amount of energy produced to the air at this frequency must be really huge to even hear it at all. Most people certainly feel it more than hear it. In fact it is somewhat of a problem in live performances as it is difficult to boost the volume at all with amplification. It is virtually impossible to find mics, amps and speakers that can all operate effectively at that frequency.

Once the bar and resonator were made it was just a matter of some simple woodwork to lift the whole thing off the ground by enough to give the bar clearance. I made a simple trestle-type a-frame for the far end and a one piece bar-frame/tube support for the front end.

Of course GUS needed to be included in a performance, so I wrote a 12 minute piece for marimbist and percussion trio called "Project Arcadia". I performed this several times in early 1998 with the other members of the Adelaide Percussion Quartet as part of the 1998 Adelaide Fringe Festival. GUS remained in place spanning the entire width of the stage in the background throughout the season.

To find out more about Project Arcadia, Visit our Products (Sheet Music) Page or email me.

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