Free Bar instrument instructions

  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


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.



Helpful references

Piano Note Designation

Note - Frequency Table

Excel tube length calculator

All content copyright 2006 - 2007, Jim Rienhardt d/b/a Museum of Light and Sound