Piezo Isolation

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Piezo Isolation

Postby Mark Wybierala » Fri Apr 07, 2017 12:16 pm

I'd like to explore building a couple of submini scale basses in the 20-22" scale range and the use of those rubbery strings. I've read that output level is low when off the shelf piezo preamps are employed and I assume this is due to the comparatively low tension and energy of these specialized strings. Boosting this output from either the preamp or even just turning up the amplification is also going to increase the level of undesirable body noises and potential for feedback. I'm wondering if anyone has experimented with methods of isolating a piezo from the body of an instrument with any type of vibration barrier.

I'm thinking of a higher mass metal bridge under the piezo element and some type of vibration absorbing material between the bridge and the wood of the instrument. What type of material is rigid yet effectively reduces the transfer of sound waves?

My current idea is to use a conventional bone saddle over a piezo element on top of a brass bridge sitting on top of a soft rubber platform and keeping the bridge in place using a nylon tail gut similar to the way a violin tailpiece is suspended from the end pin. ...Maybe a separate tailpiece. The design specifics are dependent on what I use as an isolation material and I'll need to secure the bridge into position without increasing the sound coupling in the method used to keep the bridge in place. The whole idea is to increase the ratio of string vibration acting on the piezo over body noises and vibrations acting on the piezo. This way I can employ a higher gain preamp without having some of the undesirable side effects -- I think.

Any discussion is appreciated.
Mark Wybierala
Posts: 300
Joined: Fri Feb 03, 2012 10:14 am
Location: Central New Jersey

Re: Piezo Isolation

Postby David King » Fri Apr 07, 2017 3:59 pm

The Ubass continues to enthrall so they must have solved this problem somehow.
Old-school speaker designers always reach for MDF when they want to add mass and rigidity with minimal resonant peaks. There are certainly heavier, deader materials to reach for but frankly I'd start with the pickup options and work back from there. You could easily wrap some fine iron wire over a segment of the string over a magnetic pickup. You could look at true acoustic pickups like Schertler in Switzerland makes or wind your own using a short plastic tube bridge saddle that plug each end up with an electret-condensor microphone connected to a modest mic preamp circuit. There are the Lightwave optical pickups. My guess is that the right piezo pickup will work just fine with modest isolation
David King
Posts: 2503
Joined: Sat Jan 07, 2012 10:01 pm
Location: Portland, OR

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