A free bar instrument is any instrument built with free (unattached) bars. These bars can be any material, wood, glass,
metal, etc, and any shape, rods, tubes, bars, etc. The
material should be uniform in shape for the entire instrument.
That is, the width and thickness of a bar should be the same for the
entire length.
How to cut bars for correct musical tones.
The simplest way to construct an instrument takes some guessing
and experimenting to start. Cut a reasonable length piece of
your material. For our example we will start with a piece that
is 15 cm in length. Metric measure for this process is much easier
to work with.
Rest this bar on a support material like foam or felt that will
allow it to vibrate. Tap the piece with a hard wood mallet to get a
tone. Use a piano or other tuned instrument to find the pitch
of this bar. You may have to trim the bar by filing or
grinding slightly to get a good match for tone.
Once you have this note verified, look up the frequency of the
note. (See references at the right.)
Now some math kicks in.
This formula will find the length of the remaining bars:
L2 is the new bar length
L1 is the sample bar length (in this case 15 cm)
F1 is the frequency of the sample bar
F2 is the frequency of the next new bar EXAMPLE: Our
bar was cut to 15 cm. Let's say that we found to to be an F3
which has a frequency of 174.61 Hz. We want our next bar to be a
G3 note. G3 has a frequency of 196.00 Hz. Plug these into
the formula:
The new bar length, L2, then becomes 14.16 cm for a G3
note. Support for the bar
The bar (or tube) must be supported in a way that allows it to
vibrate freely. A dense foam or thick felt pad works for
horizontal bars or tubes. If you are going to hang these for
chimes then use heavy fishing line. The bars will resonate for a
longer time if they are supported at a node. The node occurs
at 22.4% of the length from each end. It is not absolutely necessary
to support at these points, but it gives a better ring. For our
sample 15 cm bar the support points would be 15 X .224 or 3.36 cm
from each end. |