Derek McCormick’s Violin Blog

Making a violin and other violin-related topics

Closing the body

TAP TONES Before fixing the front to the rest of the body I check the “tap tones”. Every piece of wood (or any other material) has natural modes of vibration when they are stimulated by tones. The modes of vibration of a violin front can be determined by holding the front at specific points (nodes) and tapping at other spcific points (antinodes). The frequency of the generated sound can be measured either by ear (by comparing with tones of known frequency) or by using a computer program (which is much easier). Three modes of vibration (#1,#2 and #5) are of special to violinmakers because they are related to stiffness across and along the grain respectively and reppd represent the bending and twisting motions of the front when the violin is played. This allow the maker to have some control over the characteristics of the front.  By shaving off some wood inside the front or on the bass bar we can alter the mode frequency in a predictable way. There is more than one view on the value of “tap tones” to the maker and I remain an agnostic because the behaviour of the finished instrument is enormously more complex than the vibration of an isolated front. However, it is easy to do and if I gather enough data who knows – I may find a relationship between “tap tones” and particular tonal characteristics.

Screenshot

Here I have used a program called CoolEdit to record and analyse three taps placed so as to elicit mode #2. I have selected an area (white bar) and analysed the frequencies present in the sound. You can see in the insert that there is a major peak followed by a series of lesser peaks of decreasing amplitude and increasing frequency. Mode #2 of this front is 137Hz. I make a note of this figure together wih the values for #1 and #5 for future reference. I also record the weight of the front (65gm).

Closed

The front is glued on using thinner hide glue than was used for the back.

DSCF2102

The body is now complete and only needs a bit of refinement of the edges. Next step the scroll/pegbox/neck.

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May 13, 2009 Posted by | (13) Closing the Body | Leave a comment