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

[rjb]

Sidetrack

many settle on squeezing a sensor somewhere under their bridge - not an option for me.

If under the bridge were an option, is this the kind of sensor one might use?
1 Piece Sensitive Piezo Accoustic Classical Guitar Saddle Pickup Transducer Soft | eBay
Anyone?

EDIT:
Never mind; I found the info I wanted here:
http://liutaiomottola.com/PrevPubs/P...Transducer.htm

[the great waldo]

K&K trinity systems seem to work pretty good, even without a preamp and they look like all the other brass piezo transducers.

Cheers

Andrew

Not to knock your inquiring mind pesky, but lots of engineers have been through this one before and your 1. seems to be the solution that can be counted on. Without some background pressure on it, the piezo crystal seems to make a lousy transducer. Who knows maybe you'll be the one with the breakthrough.

[Achiles]

I´m after to make experinces based on this.
https://www.youtube.com/watch?v=HVLX2_4AUpw

[rjb]

K&K trinity systems seem to work pretty good, even without a preamp and they look like all the other brass piezo transducers.

I'm confused.
Sez here "The system consists of a soundhole condenser mic, an under-saddle piezo and -- the star of the show -- the Pure, a three-element body sensor pickup that attaches to the bridge plate inside the guitar"
Product Reviews | K&K Sound

[Leo_Gnardo]

I'm confused.
Sez here "The system consists of a soundhole condenser mic, an under-saddle piezo and -- the star of the show -- the Pure, a three-element body sensor pickup that attaches to the bridge plate inside the guitar"

Confused indeed, me too. If they're not piezo, then what are/is the Pure, trio of coin-shape body sensors?

And the K&K FanTaStik part of the kit - another "matchstick" piezo. You know where that goes.

FWIW Taylor's "expression" system has included non piezo "body sensors" for a dozen years now. Some sort of low-impedance coil, also in a coin-shaped container about the size of a nickel. Taylor puts 'em on the back side of the sound board, near but not directly under the bridge where K&K shows theirs. Early (@2003) expression systems had 2 body sensors plus a miniature magnetic pickup buried under the last inch of fretboard, and these 3 were wired in series (!) and sent to the onboard preamp. Since then, they've gone to one body sensor. And all of that still doesn't explain piezo anything.

[big_teee]

If you Google Piezo guitar Pickups, this is what you get.
piezo guitar pickups - Google Search
Lots of variations looks like!
T

[copperheadroads]

I have a bunch of Piezo discs & I experimented with them a little bit ,They work good on the headstock of an electric ....& not so good on a thick poly coated body

[Leo_Gnardo]

And there's this nugget of wisdom, direct from K&K's advice on feedback:

"We’ve done tests with our FanTaStick undersaddle pickup and the Pure Mini bridge plate pickup, and were able to achieve about the same gain-before-feedback with both systems. But of course, undersaddle pickups with their very “direct” and string driven tone cut better through a loud mix."

To add to this, there's the old sound guy's "NOM" advice - the larger the Number of Open Mics, the closer you get to system feedback. So adding more transducers (whether ordinary mics or strain-gage/accelerometer or piezo) works against you in trying to get gain before feedback. Read about NOM in Sound System Engineering by Don & Carolyn Davis. There ain't no free lunch, try as you might.

The evidence all leads to the same place - squeezed under the saddle. FWIW Rick Turner's "Highlander" pickups were not piezo, but electret capacitor technology, so they have a warmer, fuller tone without that annoying 5 KHz peak that's endemic to piezos. Still need a squeeze in the right place to make 'em work.

-edit-

Now I've had another look at the D-TAR DPU-3, it looks to be the only remaining solution for peskywinnets. "Can't mount pickup under saddle." - indeed, because the intended location is in the bridge pickup cavity of an electric guitar. Also with David Lindley as a satisfied customer, what else do we need to know. I'm sure with Lindley's collection of sazs, ouds, bouzukis, balalaikas & banjos there's no time to develop a different pickup system for each one. And he always sounds terrific. Sorry pesky, those brass "coin" pickups aren't going to get you much satisfaction. I'd look into the DPU-3.

If you insist on staying "low budget DIY" you could try a form of what you proposed in #12 - I'd find whatever sweet spot I could and use a trio of screws to hold the brass piezo pickup at the edge while pressing one side into the guitar wood.

[Steve Works]

If under the bridge were an option, is this the kind of sensor one might use?
1 Piece Sensitive Piezo Accoustic Classical Guitar Saddle Pickup Transducer Soft | eBay
Anyone?

EDIT:
Never mind; I found the info I wanted here:
Constructing an Under Saddle Transducer

Under the bridge works fine for me. I'll post pictures later today.

[Rick Turner]

Catching up here...

First, the Highlander was and is NOT an electret element. The original which I sourced and had custom made by NTK in Japan was a coaxial wire with piezo ceramic dust impregnated rubber as what you'd think of as being the "insulator" between the center conductor and the shield. The newer ones as well as the D-TAR (Duncan Turner Acoustic Research) is a piezo polymer (Kynar) in the same coax configuration.

Second, it's all about location, location, location and interface geometry. And then it's about proper buffering and possibly pre-amplification (for lower output sensors). There are a couple of approaches to the buffering...high-Z input FET preamps and charge amps, but if you don't get it right at that very first stage of electronics, you'll never get it sounding good. Piezos have incredible dynamic range, hence my insistence of 18 Volt buffer/preamps in the instrument.

Also, piezos make utterly lousy line drivers. You can kind of get away with passive (into a high Z external preamp or "acoustic" amplifier with a very high Z input) with piezo ceramic pickups. You can't at all with piezo polymer pickups. Kevin Beller measured a 9 dB loss in only 10 feet of decent guitar cable. It's the voltage loss to capacitive loading that kills you.

The other issue is that too much shielding is barely enough with piezos. As a source impedance, they are almost like an open circuit, and it's just so easy for hum fields to get in.

The advantage of undersaddle pickups is that they get the guitar string signal from the same location (bridge saddle) as the guitar gets the signal.

I could write a book on this stuff, but I think that once the basics are understood...then you should develop your own style.

I do not much favor SBTs...Sound Board Transducers. They are so location sensitive that they all too often sound like the sound is coming from the bottom of a resonant well. They also turn the top of a guitar into a mic diaphragm, and thus they are feedback monsters. The best of them...like the old FRAP and the Trance Audio systems...wind up mounted in pairs directly under the bridge saddle on the bridge plate.

[rhgwynn]

I used to have a Washburn bass that was all piezo. It had the strip under the bridge assembly, and each individual saddle had a piezo button epoxied into a recess on the bottom. The tiny wires broke off one or two, so I had a chance to take a look. It seems to me that for a piezo disc or button to work well, it needs to be firmly secured and have solid contact with the vibrating surface. I managed to clean them all out, and they were VERY firmly installed. Maybe a recess and epoxy is the answer here? I'm not sure about different epoxies abilities to help or hinder the buttons ability to pick up the vibrations but, there you have it. The bass did have a preamp - their so called Advanced Bass Technology.

[Rick Turner]

A few pithy comments:

If you're working a piezo pickup in pressure mode, then they work best with a decent pre-load of string pressure to mechanically bias them into a good linear output mode.

If you're working in shear mode, you just need enough down pressure to keep extraneous rattles out of the picture.

The best results happen when the foundation/mounting of the pickup is very, very solid.

The best results happen when the vibration input to the top of a piezo block is as isolated as possible from the foundation/mounting of the pickup.

Too much shielding is almost enough.

There can be "magic ratios" of closeness to the strings vs. closeness to the top on acoustic instruments.

Area counts.

When closely coupled to the strings, piezo pickups have significantly better phase response to string vibration than the instrument itself...for better or worse.

The frequency response of piezo pickups makes magnetic pickups sound like early telephones. We're talking whales to bats here.

If you do everything right and still don't like the sound, then it's location, location, location, OR you just don't like to hear phase coherent string signals. And then you'll have to go into the DSP realm to deal with it. That's why I proposed the Mama Bear DSP acoustic guitar preamp, first to Martin Guitars (Chris didn't like it when I said it was possible to make an Ovation sound like a D-28...but it is...), and then to my pals at Seymour Duncan. Hence D-TAR and the Mama Bear project.

Don't bother with all the math. Make, properly buffer, and listen.

Play with load impedance to control low end. It can be too much. Shunt resistance across the pickup makes for a high pass filter. See previous comment re. the math. Just substitute different resistors. I've even done three position load switches for extreme low end tone control.

[Bruce Johnson]

Here's an analogy that may help:

Think of a piezo element as being a hollow rubber bulb with a tube coming out of it. When you squeeze the bulb repeatedly, you get pulses of air coming out the tube. The harder you squeeze, the bigger the amplitude of the pulse. But if you just glue the bulb firmly onto a vibrating surface, you won't get much signal. The bulb needs to be squeezed, squashed, or significantly bent between parts that move in relation to each other, to get pulses of signal.

The mechanical side of designing a piezo pickup is all about applying physical movement to the element. You can't just hang the element somewhere and expect it to pick up sound. It has to be mounted down solidly AND have a separate vibrating part pressing on it, causing it to squash or bend. The bulb has to be squeezed. Mounting element in the bridge, with a saddle block on top of it, is one of the obvious ways to get that squashing action. If you mount it somewhere else, it has to be between moving parts.

Now, some pre-made piezo pickups already have been made to create that squashing/bending internally. For example, most large disk pickups are made to be attached to a surface. But, they depend upon the disk flexing and bending to make signal. The amplitude of the movement applied to the disk will determine the amplitude of the signal. Mount it squishy and the signal will be squishy. Mount it to something solid and immoveable, and there's no signal.

I learned all this from working with Rick on some systems for my basses, back in the 1990's.

[big_teee]

Thanks Bruce.
T

[rhgwynn]

It was surprising to me when Rick said that piezos held auditory superiority over magnetic pickups; given that most people think of them as weak and tinny - at least, they are when not used properly. But after I took a moment to think about it, it kinda makes sense. There is no electronic interference picked up, which cleans up the signal; noise tends to get worse the more pedals you use, and can be a big problem when you are dependent on them for your sound. The downside might be if you are too noisy against the soundboard or wherever the sensor is mounted, that sound would come through. I'm sure there are more but I'd rather not speculate.