Just a quick idea that came to my mind this evening. A couple of weeks ago I was using a cheap piezo disc, recycled from a broken smoke detector, to try and generate some ultrasonics up to 100kHz. The reason was to test a 1/4" microphone capsule with a quickly hacked together mic preamp for their suitability to capture the sounds of bats. I'm not quite satisfied with the results yet, but it kinda sorta worked okay for a first test. Of course there's a hen and egg problem here, since I neither know the frequency response of the mic, nor the piezo disc. The response was quite rough, but I was totally able to get up to the 96kHz recording limit of my sound card with no effort.
So now I thought about what might happen if I use this piezo disc instead of a vinyl test record, place the needle on top of it, and play a frequency sweep.
The piezo disc was connected directly to the output of the soundcard (a Scarlett 2i2) and excited full steam with -3dBFS output from Room Equation Wizard. The phono output went through a diy RIAA preamp connected back to the soundcard input and the following response recorded:
Looks pretty rough, but the part between 18k - 28k is somewhat interesting. It seems to suggest a useable response up to 23kHz without an early peek or drop.
My quick'n'dirty test setup is certainly far from ideal, but maybe there's some potential to achieve some better results? The main reason here would be to observe the range from 15k - 25k to fine tune the input capacitance of the preamp.
So now I thought about what might happen if I use this piezo disc instead of a vinyl test record, place the needle on top of it, and play a frequency sweep.
The piezo disc was connected directly to the output of the soundcard (a Scarlett 2i2) and excited full steam with -3dBFS output from Room Equation Wizard. The phono output went through a diy RIAA preamp connected back to the soundcard input and the following response recorded:
Looks pretty rough, but the part between 18k - 28k is somewhat interesting. It seems to suggest a useable response up to 23kHz without an early peek or drop.
My quick'n'dirty test setup is certainly far from ideal, but maybe there's some potential to achieve some better results? The main reason here would be to observe the range from 15k - 25k to fine tune the input capacitance of the preamp.
Very interesting. Alas, the piezo disk has frequency dependent vibration modes. Because of this the stylus can sit on a minimally or a maximally vibrating part.
https://www.researchgate.net/figure...-modes-of-a-piezoelectric-disc_fig2_324677066
https://www.researchgate.net/figure...-modes-of-a-piezoelectric-disc_fig2_324677066
Not all that meaningful, I guess.
Here are some more results with different placements of the stylus on the disc (this time on the ceramic side, though), with the disc either sitting on the turntable or dangling in free air, only suspended by the cable run attached to it. The smooth black trace was recorded with the stylus close to, but not making any physical contact to the piezo disc.
Here are some more results with different placements of the stylus on the disc (this time on the ceramic side, though), with the disc either sitting on the turntable or dangling in free air, only suspended by the cable run attached to it. The smooth black trace was recorded with the stylus close to, but not making any physical contact to the piezo disc.
Hm, I had the very same idea a while ago. Thank you for trying it. I think it could be developed further by measuring the acceleration at the stylus tip by some optical method (laser + photodiode?) and controlling the excitation by negative feedback.
