Piezo sensors... "Pressure, pushing down on me"

[Leo_Gnardo]

Yes. Actually, he used to post here, so it may be possible to ask him. He may also have patents.

And I hope Mr. Turner will return & enlighten us sometime.

In any case, a useful scrap of knowledge Rick passed along to me @ 1994 is that the typical piezo "matchstick" pickups, as well as his own "Highlander" pickups, required a fair bit of pressure to start with. The guitar signal could be interpreted as a delta function, or CHANGE in pressure. Which leads to locating them under the saddle where there's plenty of static pressure as well as changes in pressure due to string movement. A carefully cut flat-bottomed saddle groove is a good place to start, as well as having a saddle that isn't so wide the strings won't push it down into the pickup.

Early Barcus-Berry and FRAP pickups were simply stuck to the back of a guitar's soundboard with various glues or removable adhesives - and needed massive preamp gain & skilled (lucky) placement to sound like anything. (Some avant-garde musos stuck 'em anywhere & everywhere - I read of Frank Zappa having piezo's in his headstock but who knows if that ever made it to record - might have worked if squeezed under the nut.)

[Joe Gwinn]

And Rick Turner interviews.

Yes. Actually, he used to post here, so it may be possible to ask him. He may also have patents.

[rjb]

Search Fishman's early patents.

And Rick Turner interviews.

[Joe Gwinn]

Search Fishman's early patents.

More generally, there are lots of piezo guitar pickup patents, so one can get a good survey of the various approaches.

[eschertron]

what I've tried...

Double sided tape - weak signal
Drill a hole in the middle of the sensor & then screwing down so that the piezo presses firmly against the guitar body - weak signal
Attaching the sensor to some FR4 & mounting the fr4 to the body - weak signal.
Physically holding the sensor whilst randomly pressing its brass disc against the body - occasionally I hit a sweet spot (not on the body, but more angle/pressure of the sensor) & the sound level/signal leaps up & is "fuller" than a fat bloke who's had 10 courses of high calorie fat stuff, but hasn't farted yet.

This last test/result proves my fet preamp is fit for purpose & that a nice signal can be coaxed out of the pickup cavity.

I'd rather not deal in randomness...indeed, it'd be impossible to replicate the mount position/pressure when I hit that whimsical sweet spot of pressure/angle ...so rather than just hit & hope, I'd rather try & fathom out the best approach.

Ok - Piezo sensors....so the white piezo material reacts to pressure/vibrations.....what is the brass disc's purpose here? Would it be safe to say that we ideally want the brass disc to stay as static as possible with only the piezo material getting the vibrations?

Top tips warmly received.

From the other posts (and the experiments I'vre tried) I'd say that any weakly-coupled arrangement, like the double sided tape, will be a poor conductor of pressure waves. And my intuition suggests that, from the edge-only and edge-like-a-diving-board experiments, that the piezo reacts more strongly to vibrations laterally across its surface which is why the center-mounted experiment was also weak. When the piezo is part of the pressure wave transmission from the strings to the acoustic space (glued under the bridge, or as part of the sounding board) it seems to work the best. It's not a point sensor, but rather a surface sensor. Get as much of the piezo surface vibrating as possible.

[peskywinnets]

I found I got the best results by twanging the disc like a diving board. I fixed one edge to the guitar body and attached a small weight (a "seismic mass") to the other edge 180 degrees opposite. This gave by far the biggest output of any configuration I tried. The different bending mode and added weight lowers the resonant frequency, giving a fuller sound with more bass.

That ties in with my own tests...the best sound I got was actually with one edge of the brass disc pressed against the body & the opposite end angled up off the body.

When you say they expand & contract in the radial direction (forgive my lack of grasp here!)....you mean the piezo material expand/contracts along its diameter line?

JM...they may well react to straight pressure...but I couldn't get any meaningful level out of the sensor with all the direct pressure permutations I tried!

[J M Fahey]

Agree and add: they are *also* sensitive to straight pressure.
FWIF I have successfully:
a) sandwiched the disk between my cheap nass bridge (which basically is an "L" bent piece of 1/8" iron sheet) and bass bosy: strong humless signal, both because it gets it in full amd the grounded bridge shields it
b) on my nylon string Spanish guitar I Krazy glued it on the inside under the bridge, after I found a sweet spot.
Got good signal, yet as an experiment I krazy glued a coin to the free surface, it significantly raised output and gave me a lot warmer sound.

I used "Gel" type krazy glue, not the watery usual type.

[Steve Conner]

Those piezo disc beepers are designed to bend. In use, they are clamped around the outside circumference of the brass disc, the way a drumskin is attached to a drum. The piezo disc expands and contracts in the radial direction, causing the brass disc it's bonded to to bow in and out, again like a tiny drumskin, with a resonant frequency of a few kHz, as required for making beep sounds.

I found I got the best results by twanging the disc like a diving board. I fixed one edge to the guitar body and attached a small weight (a "seismic mass") to the other edge 180 degrees opposite. This gave by far the biggest output of any configuration I tried. The different bending mode and added weight lowers the resonant frequency, giving a fuller sound with more bass.

[peskywinnets]

So I've been dabbling with piezo sensors...and they've been messing with my head.

Re mounting piezo sensors, if you read everything that abounds on the net there's much conflicting info (no surprise) ....many settle on squeezing a sensor somewhere under their bridge - not an option for me.

I actually wanted to mount a piezo sensor in my bridge humbucker pickup cavity against the body of my solid body electric ....but I can't get the mounting arrangements right, what I've tried...

Double sided tape - weak signal
Drill a hole in the middle of the sensor & then screwing down so that the piezo presses firmly against the guitar body - weak signal
Attaching the sensor to some FR4 & mounting the fr4 to the body - weak signal.
Physically holding the sensor whilst randomly pressing its brass disc against the body - occasionally I hit a sweet spot (not on the body, but more angle/pressure of the sensor) & the sound level/signal leaps up & is "fuller" than a fat bloke who's had 10 courses of high calorie fat stuff, but hasn't farted yet.

This last test/result proves my fet preamp is fit for purpose & that a nice signal can be coaxed out of the pickup cavity.

I'd rather not deal in randomness...indeed, it'd be impossible to replicate the mount position/pressure when I hit that whimsical sweet spot of pressure/angle ...so rather than just hit & hope, I'd rather try & fathom out the best approach.

Ok - Piezo sensors....so the white piezo material reacts to pressure/vibrations.....what is the brass disc's purpose here? Would it be safe to say that we ideally want the brass disc to stay as static as possible with only the piezo material getting the vibrations?

Top tips warmly received.