Detuning/widening bandwidth of piezo transducer?

Agree. Fixing it mechanically is likely better than trying to patch up a high Q response after the fact. First thing I'd try is to run the piezo into the virtual ground of an op-amp. But the intrinsic series impedance of the transducer may make this unfruitful. May have to resort to mechanical damping. Glue the piezo to a piece of foam rubber and load it with a horn as described above.

I have a commercial ultrasonic leak detector. Can't see in the hole too well, but it looks more like a plastic dome on a voice coil than a piezo transducer. The transmitter and receiver transducers "look" to be the same, but that's not necessarily a valid conclusion. I never found any data on the setup, so don't know what the claimed bandwidth is.

Might be interesting to plug on a capacitor microphone element and see what that does. Most of the microphone specs I've seen are still going strong at the 20 KHz. end of the graph. mike

Hi all,

I recently posted about a bat detector (read ultrasonic pitch downshifter) I'm building from the following schematic:

My goal is to build it without the indicated coils. Bob Eldred showed me the light on getting rid of one of the coils, reminding me that the 47mH coil and its cap were simply a passive LPF, which I then replaced with an active Sallen Key LPF (TL072 and some resistors/caps).

Now my detector works quite well. I can easily hear several harmonics from my TV, my pocket chain clinking sounds REALLY weird, etc. But I want to see if I can improve the bandwidth of the piezo UST.

Bertik (author of the schematic) has a good page on how to do this with caps, resistors, and a 5-8mH coil, but before I get into trying to make the coil, I was wondering if there are any active/non-coil ways to do it.

Any answers/tips/links appreciated,

Torben

P.S. I've googled/teoma'd/mootered for this a million times, but either the answer's not out there or I didn't recognize it for what it was.

Lars Torben Wilson wrote: snip

Good place for microphones is an old cellphone, cordless phone, cassette tape recorder... mike

OK, that's two votes for the horn, so it's probably not a bad idea at all. However, I have both a space limitation and a horn-manufacturing limitation, not to mention a limitation in my understanding of acoustics which I figure would help me work out the size needed for best performance from ~30kHz to ~100kHz. Quicky paper horns (pretty much linear) seem to help with the sensitivity, though.

I'll give that a shot on my breadboard. I still have to check the actual response of the transducer; I've been assuming so far that it has a fairly tight spike around 40kHz, but I've also read that some work just fine with no detuning at all. Given that I'm already fairly happy with the sound, what I'm trying for now is to solidify my understanding of the detuning. I'm currently under the (probably wrong) impression that it's mostly phase games. Am I close?

Cool.

Hm...that sounds neat. I'll see if I can find one.

Thanks for the tips,

Torben