We sell piezo material in several forms for making musical instrument pickups. One form is cable, about a tenth of an inch in diameter. The piezo cable looks very much like regular shielded audio cable, but it’s got a very thin layer of piezo material inside which enables it to function as a contact pickup. It’s most often used in or under the bridge of string instruments, where it can respond very directly to the string vibrations.
For a typical guitar installation, you need a piece of cable about 5″ long to span the bridge with enough left over to make the necessary connections. But our customers have occasionally wondered: how much longer can a piece of piezo cable be, and still work well? Imagine for example that you’re making something like a clavichord or harpsichord; can you use a single piece of piezo cable several feet long to pick up the sound from the full length of the bridge?
I recently performed some tests to see how length affects the performance of the cable. Mind you, the tests were very rudimentary. I didn’t build harpsichords to test them in; I just cut pieces of the cable to various lengths and hooked them up to an amplifier. I tested and compared their outputs by wedging them under the strings of a guitar and plucking the strings. Here’s what I found.
Finding number one: Length doesn’t seem to be a problem. Long cables were about as responsive as short ones. The longest I tested was 48″, and the strength and quality of the response was not very different from that of a 5″ cable.
Finding number two: Regardless of length, the cables do not produce a very strong signal. Theoutput is less than that from the piezo films that we sell. (This wasn’t really news, but these tests confirmed it for me.) That leads to these two pieces of advice: 1) Piezo cable is best used in applications where it can be given strong vibrations to respond to (such as in-bridge installations). 2) In installations using piezo cable it’s especially important to make sure all wiring is well shielded, to provide the best available signal-to-noise ratio.
In spite of the lesser signal strength, plenty of customers have gotten back to me to report very successful applications with the cable.