Interesting discovery regarding a junkbox piezo element…

Published on 2012-01-21 by Mark VandeWettering

I was tinkering with a small electronics project (article and video to come) and needed a sound output. Digging around in my junkbox, I found one of these piezo speakers, and decided to use it, driving it with a square wave from my Arduino:

Piezo Element 1500-3000Hz – RadioShack.com

My initial test was supposed to be 700 Hz, but it sounded very high. I recorded a sample with Audacity and looked at the spectrum, and sure enough, it’s principle frequency was at 2100Hz. I then looked at the driving signal using my Rigol DS1102E (did I mention I got a new scope this week?) and sure enough, it was a nice 700 Hz square wave. Apparently the specifications on this little piezo element weren’t kidding: it has almost no frequency response below 1500Hz, so all you end up hearing are the third harmonic. The fifth harmonic is actually pretty weak too, so you end up with a pretty even sine wave, just at the wrong frequency.

I guess if I want higher quality sound out of this thing, I’ll need to rig a real speaker.