Prepared for EE107: Projects in Music and Science
We built a "bare-bones" electric violin and used it to study the effects of different bridge materials, bridge styles, and pick-up styles on sound.
The violin body was built from a red oak 1"x3". The pegs were made from 5/16" dowels, tapered on one end and filed on the other so that square grips could be attached. At the base of the violin, the strings are held in place by four notched dowels, set in angled holes. (We originally drilled these holes too close to the the bridge and later moved them back -- that's why there are two extra holes in the violin body.) A cross-piece was added to the base of the violin to form a base for the shoulder rest.
The main problem encountered in the violin's construction was that, due to the shallow peg box design, the strings would not lie flat against the nut. Because they were not fully stopped at that end, they buzzed badly. We solved this problem by raising the fingerboard and by adding a strip of wood over the end of the pegbox to hold the strings down.
More details on the violin's construction can be found here.
The design for the piezo-electric pick-up came from this webpage. Although a number of different pick-ups were used throughout the project, the basic design was the same: a piezo-electic disk (removed from a buzzer) was soldered to a length of shielded audio cable, and the other end was connected to a plug (either RCA or mini audio plug).
Piezo pick-ups work by flexing. They are often placed on the body of a traditional violin, but in our solid-body design, the bridge was the only part that vibrated enough to generate a signal. We found that white glue was an excellent adhesive, attaching the pick-up to the bridge very fimly (which made for a better sound), but not permanently. However, we wound up using double-sided scotch tape to attach the pick-ups in the recordings below, since we wanted to re-use the same pick-up on many different bridges during the recording sessions. The double-sided tape is not as strong as glue and dampens the sound slightly, but not significantly.
To see whether different piezos would produce different sounds, we tested three pick-ups on the original red oak bridge.
We concluded that the size and shape of the piezo elements does affect their sound output. Smaller-diameter piezos produced less volume, and thicker piezos produced a lower-quality sound.
We used the electric violin to test bridges of a variety of materials, widths, and designs. Since we had determined that different piezo pick-ups produced different outputs, we tested each bridge with two pick-ups. (Piezo A is the "large, thin pick-up" from the list above, and Piezo B is the "small, thin pick-up".)
We found that, in general, stronger materials seem to produce a better sound, probably because they conduct vibrations more faithfully (compare poplar, a very soft wood, to red oak, a very hard wood). However, the aluminum bridge, although strongest, was also the most dampened. This may be because it was also the heaviest bridge, and hence did not vibrate as much under the same force from the strings.
We'd like to expand the results above by taking a better look at the relationship between bridge weight and sound. For example -- what would an aluminum bridge sound like if it were as light as the wood bridges? Would it still produce a dampened sound?
We also hope to further explore the effects of pick-up size and style on sound. It would be interesting to know whether even thinner pick-ups would produce even better sound, and to see whether the sound from smaller-diameter pick-ups actually varies from that of larger pick-ups if both are amplified to the same volume.
We would also like to expand our experiments to include different types of strings. So far all of the experiments have used low-quality steel strings; a different string material might produce interesting results.
There are two easy ways to avoid the problem of the strings not lying flat against the nut. One option is to build the violin from a thicker piece of wood (maybe 2"x3") -- this allows you to drill the pin holes a good deal lower than the nut (rather than nearly flush with the nut, as in our design). The other option is to drill the pin holes such that the one closest to the nut is closest to the top face of the violin, and then string them so that the string comes out from under the dowel (as versus over the top of the dowel in our design).
The main problem with piezo-electric pick-ups is that they are delicate. In particular, the solder joint on the porcelaine of the piezo is very weak, and it takes out a chunk of the porcelain when it snaps. You can help take the stress off this joint by making the wire connecting to the porcelaine a little longer than the one soldered to the brass. It's also important to solder piezos with low heat (20-33 Watts seems to work well), and to minimize the time the iron is in contact with the disk.