furious contact microphone additional info:
I received an email suggesting that a good way to make an underwater contact microphone is to dip the whole piezo element in "dip-it" - the liquid latex that is sold at hardware stores and is commonly used to coat the handles of tools. Somebody placed such a microphone within a block of ice and recorded the sounds as the block melted when thrown into a bucket of hot water. I lost the email that told me about this work - if anyone can credit the artist who did this experiment, I'll update this note.
Here is an email that I received concerning using a transducer versus using a buzzer element:
I am looking at the packaging on the 273-073A
(I have a bunch of these and don't use them anymore) and they are designed
to emit a 2500hz tone +-500hz. Therein lies the problem with them. Transducers,
as I'm sure you know, are a two way street. The unit was designed to produce
one frequency and also (when used as an input unit) is primarily responsive
to that frequency so what you're getting is probably 2000-3000hz with some
leakage around those frequencies. I am looking at another Radio Shack part
273-091B and the packaging states that the frequency range is 700hz to
10khz. These are larger and the frequency response is infinitely superior.
Once again, they come in a case that you have to break open. There is one
problem. Within the last 2 months Radio Shack has "discontinued" this model
in their stores. I bought as many as I could but am running out of them
fast. So I am presently in a search for another source for these items.
Take a look in your local Radio Shack and maybe you'll get lucky and they'll
have a few left. I highly recommend them over the buzzer. One telling sign
is that the former unit is labeled a Piezo Transducer while the latter
is labeled a Piezo Speaker
Element. As a speaker element it is designed to cover a wider frequency range. I have found some other elements that are not designed for one frequency, but so far these are the widest range I have found. I have used them on acoustic guitar and also on instruments that I design and build and have been nothing but happy with the results. I still tweak the hell out the sound for the acoustic but I also do that with conventional mics like the AKG 414 because of the way I like my guitar to sound. As for the instruments I build, I love these mics and just run them flat with no effects. If you would like to look at some of my creations, go to xochi.com/ims. <snip>
Paul B. Cutler