Piezo feedback problems

Replies to This Discussion

Permalink Reply by Mark Werner on March 12, 2009 at 7:11pm

The piezos do appear to be quite sensitive to amp settings. I find that if I have any of the controls up too high, feedback is quick to occur. Any overdrive setting appears to be critical.

Folks have tried various dodges to avoid this; mounting the piezo on a piece of foam, isolating it in silicone gel...etc.

Permalink Reply by David Fultz on March 12, 2009 at 8:05pm

Thanks Mark. Sure to give those a try. I'll have to experiment i guess to find the best solution.

Permalink Reply by David Fultz on March 12, 2009 at 8:08pm

Does this drop the pickupability (like that word? lol) Is it totally encased in gel or caulk?

Permalink Reply by Wesley Dean on March 13, 2009 at 6:33pm

I use Dap weldwood contact cement. I have not had a issue with any feedback. If anything I definatly get an all around better sound. Just add a bit to both contact points with a brush, then join, press down ever so gently and hold for 20-25 seconds. Lift the piezo off and hold for 30 seconds. Then press the piezo back on, and Swirl(tech term for rub it around in circles) the piezo on the surface (this will guarantee total contact) for 5-10 sec and hold gently you are not a bear dont act like one. It takes about 15 -20 min to dry. After a solid 2 min of holding you can let go, if it slips hold longer.
Wesley Dean

Permalink Reply by Roosterman on March 14, 2009 at 6:11am

As a newbie, can someone explain the do's and dont's of piezo encasement? I cant quite figure if the whole thing is completely encased in contact with its 'encaser' (probably not the correct terminology lol) , or if the piezo should sit in a cavity so its encased, but with nothing touching the face?

Permalink Reply by Doc Oakroot on March 18, 2009 at 10:32am

Generally, you want really good mechanical connection to the strings (i.e., the bridge saddle) and as little connection to the box as possible. That will minimize feedback. So direct contact with the bridge and foam separating it from the box.

As a practical matter, piezos naturally have some brittle high freq stuff that's hard to control down the line. It helps to put something that mechanically absorbs high freq between the piezo and the bridge. (I use a rubbery, space filling, jewelry glue so there's a layer of the glue to mechanically insulate the piezo.)

Wiring two piezos in series will also help tame the high freq.

After trying everything, what I actually do most of the time is use 1 piezo, glued with a blob of jewelry glue, inside the box right under the treble foot of the bridge. No need for foam since the air in the box actually insulates the piezo from any extraneous movement in the box (piezo's don't pick up air movement very well). No feedback problems at the moderate amp settings I use on stage. They would feedback in front of a stack turned up to 11 - If I played that way, I would fill the box with foam to prevent it vibrating at all and build the piezo into the bridge ... or just use an electromagnetic pickup.


RandyRoosterGuitars said:

As a newbie, can someone explain the do's and dont's of piezo encasement? I cant quite figure if the whole thing is completely encased in contact with its 'encaser' (probably not the correct terminology lol) , or if the piezo should sit in a cavity so its encased, but with nothing touching the face?

Permalink Reply by David Fultz on March 18, 2009 at 7:57pm

Thanks to everbody for the feedback..I'm very grateful. Rock on!

Permalink Reply by Sven Pfitt on June 25, 2009 at 12:24am

One possibility is you may have a resonant enclosure problem.

For instance the RS 273-0073 is spec'd to have a resonance of 2500+/-500Hz. The center frequency of 2500hz has a wavelength of 1100f/s / 2500/s =0.44ft = 5.28". The range is 2000Hz to 3000Hz, so the range of sizes can go from 4.4" to 6.6" .

If this piezo transducer is placed in the center of a 5.28" wide box there is a strong probability it will squeal at 2500Hz if it gets enough feedback from the amp.

The solution is to move it off center. This has the unfortunate side effect of changing the tonal response.

What is the size of your cigar box?

Sven.

Permalink Reply by David Fultz on June 25, 2009 at 10:36am

Damn Sven thats all too technical for me, but it was an 8 in. sq. box

Sven Pfitt said:

One possibility is you may have a resonant enclosure problem.

For instance the RS 273-0073 is spec'd to have a resonance of 2500+/-500Hz. The center frequency of 2500hz has a wavelength of 1100f/s / 2500/s =0.44ft = 5.28". The range is 2000Hz to 3000Hz, so the range of sizes can go from 4.4" to 6.6" .

If this piezo transducer is placed in the center of a 5.28" wide box there is a strong probability it will squeal at 2500Hz if it gets enough feedback from the amp.

The solution is to move it off center. This has the unfortunate side effect of changing the tonal response.

What is the size of your cigar box?

Sven.

Permalink Reply by Jerryrig240 on January 12, 2010 at 6:27pm

Wrap your peizo in a hanky inside of the guitar. Now the peizo floats in there and it is not touching anything, but it also picks up the sound too as well. It does give the box a deeper tone as well.

Permalink Reply by Mark Mercer on January 24, 2010 at 10:08pm

Piezoelectric transducers seem inherently "tinney". I have used a capacitor across between + and - wires. the one I tried is called an "Orange Drop". It it like turning the treble way down. The bridge seems to be a good choice(as opposed to a "top"). It might be cool for some, to use a neck or even peg-head placement.(gets fret/left hand percussion). A blend knob could be used. I don't know much about capacitors, just salvaged a bunch and test. I sort in three piles, 1. no effect, 2. no sound, 3. tonal modification. Some of my experiments with phonograph cartridges has been profitable. There again they use a tone modification. I took one out of the turntable. I think I will soon use a whole tone arm, just for the "look"of it.

Permalink Reply by YeahDoIt on July 21, 2010 at 7:27am

Did anyone try making a feedback-bucking piezo pickup by connecting two piezo pickups out of phase?

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