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Old 22nd January 2003, 07:34 PM   #31
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Nice to have an expert on board! And good info.

So the performance of a piezo pickup is largly dependent on the implementation and there is no fast way to get it right. Ideal for DIY I would say.
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Old 7th April 2004, 03:43 AM   #32
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Default piezo disc acoustic pickups

I have put piezo discs on guitars, banjo, & dobro, with some very good results.
This is what I have observed, but I don't claim to have the ultimate answers.
The body of your instrument acts as an amplifier, filter, and distortion unit. The acoustic sound of your instument comes from an infinite number of point sources on the soundboard and body. All can have varying phase, tone, and amplitude. A single pickup can never reproduce this sound. A pickup near the bridge will give that harsh squacky electric sound and transmit string noise since it is only hearing the string sound like an electric guitar.
More pickups (I am using 3) reduces the amount of gain required and gives a more complex tone which I think sounds more acoustic. Also feedback and string noise are less. Generally I have found it is best to place pickups far away from the bridge (except on dobro and maybe bass). I think my guitar setup is a lot better than commercial pickups I have used and heard but I sure don't know everything.
I can't understand how a bridge transducer can pick up anything but the pure string sound which is not usually what you want. It is the most obvious approach and I tried it first myself. You really want the sound of the box.
A lot more experimentation is neccessary and I would like to know what anyone has learned.
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Old 15th April 2004, 08:14 PM   #33
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Default peizo preamp?

in order to use a peizo as a mic, would you have to build a preamp? I'm thinking it would be cool to use them as drum triggers.. or whatever they are.. but how hard would that be?
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Old 1st May 2004, 05:17 AM   #34
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There are actually two ways to get the flattest electrical response out of a piezo (the mechanical response will still have resonances, of course). One is to connect the piezo to a very high input impedance amp, as mentioned earlier in this thread. If you use this technique, choose the amplifier input resistance (R) high enough to put the -3db corner frequency with the piezo's self-capacitance (C) at or below the lowest frequency of interest:

R = 1/(2 pi f_lowest C)

This can be hard to do with a physically small piezo, which can have quite a small capacitance, and consequently may require a very large R.

The second method makes use of the fact that the output current of a shorted piezo has a rising +6dB/octave response - basically, every time the piezo is flexed it makes a certain amount of charge, so if it is flexed more times per second (ie at higher frequency) it makes more charge per second, which is to say, it makes more current. Well, if you feed this current into the input of an op-amp wired as an integrator (which has a -6dB/octave falling response) you get a flat output response.

The advantage of the second method is that due to the very low (ideally zero) input resistance of an integrator, hum and electrical noise pickup is often drastically reduced.

Some years ago I spent a few months building active feedback subwoofers, using cheap piezo disks as accelerometers to sense the loudspeaker motion. With a little work I was able to make a sensor that was completely flat within a fraction of a dB from about 10 Hz to around two kHz, when the first mechanal resonance showed up. For my application, that was not an issue, because the woofer I was working with had its first cone break-up mode at about 1 KHz, and so there was no need for more bandwidth than that anyway.

How did I know the sensor was almost perfectly flat? Because the finished subwoofer had a close-miked frequency response flat within about +/- 0.1 dB from about 30 Hz to 250 Hz, fallling off gently above and below that. Measurements were made with my then employers $5000 Bruel and Kjaer measurement microphone and various measurement systems (an AT system 1, for the most part, though I also used MLSSA).

Of course, in-room frequency response suffered from the usual room modes. But that sub still produced *very* tight bass - drum sounds were often too tight with many commercially available music CD's, which had probably been mixed on monitors which had more bass "hangover".

Sad to say, the company I worked for at the time never did anything with my prototypes. Oh, well. Ces't la vie!

-Flieslikeabeagle
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Old 11th May 2004, 04:07 AM   #35
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to flieslikeabeagle

Can you share a schematic for the opamp integrator? Is there a place where I can find one?

Thanks, Rudy8020
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Old 31st May 2004, 04:03 PM   #36
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Default contact mic building for dummies

new to forum, dont know what piezos are, but have been wondering about the seemingly endless possibilities of contact mic scenarios for a while......

you did provide instructions in the original thread, which were helpful (if only to learn that this could, possibly, be achievable), but i am neither electronically inclined nor very intuitive.

could you please break down the process of physically BUILDING a contact mic a little more? parts needed, suggestions, etc...

is it not much more than a minor adjustment to a guitar pickup?

any info/instruction/tutelege would be GREATLY appreciated.

thanks, bill
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Old 8th July 2004, 09:51 PM   #37
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Default getting a clear tone with piezos, but maybe not the best tone

hey all.

I started playing with the piezos about 5 years or so ago. I had a POS 80 dollar nylon acoustic I used as the test mule.

I glued about 5 of them in and wired and on off switch to each one. I found some combos seemed to work well. but mainly I have to say I liked the 1 inch away from th elow E string loaction under the bridge. I even tried putting a telephone mic in the guitar.

I decided to push it further and build a piezo for each string. I put this on an electric guitar body, and SG copy because the bridge is so big.
so I got an all wood bridge from stew mac, (the arch top model) and cut the piezos into 6 thin strips.
I cut them with scissors, it can be done.
I soldered the wires to the piece first. then epoxied them on because they will break off when you cut it, then cut it to size.

I built 6 strips, and attached them to the back side of the wood bridge, so that the metal would fold over the top of the bridge, and hang down on the backside. this puts all the strings in direct contact with the back of the piezo (the metal part)and the sound travels through it amazingly well this way. it might not have that sweet tone, but it is very clear. Yes the wires hanging off the back were a mess too.

And yes, folding the piezoz over on the bridge cracks the crystals, and makes the part after the bend non amplifiable, because it is broken, but the metal backing side does a good job of sending the vibration to the working part of the piezo.

I split those outputs on the 6 piezos in to sets of twos. meaning I had 2 leads or positives, or red wires comming off those piezos. I intalled 2 sets of micro switches (these have 8 mini on off switces in them and a re really small. similar to the ones inside a garage door open remote) and wired the piezos in stereo.
to be clear, I had a right and left comming off the piezo. each lead ran into an on off switch, then those ran to the left and right output jacks.

this allowed me to put certains strings on the left channel, and certain strings on the right channel. I really liked 135 on the left 246 on right. makes for a cool sound.

I am going to try some more on this. I am attempting to build my own guitar, and I will build the bridge like a classical style bridge, and hope to have all the piezos and wires hidden in the bridge this time, yet have a seperate pieze per each string, and be capable of going stereo output. I had some ideas, I will post more later if they work out.

I also am going to try throwing a mike installed inside the guitar into this. maybe I can get a cool mix of sound. dont know.

Some other ideas were possible triggering of drum triggers with the guitar strings using the piezos. I have a cheap electronic drum set that is triggered with piezos. I have been thinking about hooking it up so the guitar triggers the drums. but that is another things I need to test, and then wonder why I would even do it. lol
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Old 4th March 2005, 07:46 PM   #38
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Default Experience with Piezos

I'm new to this forum so forgive me if I am repeating an application I've used with GREAT results.

Using the inexpensive piezo disk from Radio Shack ($1.49...recently raised to $179) I carefully remove the disk from the plastic housing. I solder a shielded cable to the disk and make a strain relief using pretty heavy, stripped solid core wire. I wrap a small loop around the cable and shape the ends of that loop around the edge of the piezo. If the disk is to be removed repeatably, I'll solder the solid wire around the entire disk to make it sturdier. Then I use a thin coat of epoxy over the top of the piezo to make it truly roadworthy.

In amplifying a violin, cello or upright bass, the BEST place to attach the piezo is on the BACK of the instrument, right where the soundpost hits the back.

The vibration of the bridge is focused at that spot. There is none of the finger noise and squeaks that occur when using a piezo on the bridge.

When using a piezo on the back of the upright bass, you may have to roll off the low end, depending on the construction of the bass.

I ran across this application many years ago. Emerson, Lake and Palmer toured with a symphony orchestra. They needed a way to amplify and record many, many stringed instruments. The musicians were not happy with anything attached to their very expensive instruments. The sight of something put on the bridge was troubling.

So they took the then common Barcus Berry piezo pickup (a little rectangular pickup) and attached them to the back of the instrument as I mentioned before.

The tone possible with this application is remarkable. With my upright I needed to "plug" the F-holes to reduce feedback. I used some heavy black, dense foam (a type used to insulate steam and water pipes in industry). I cut two foam pieces just slightly larger than the F-holes. I trimmed a shallow V channel on the sides of the foam. After the foam was inserted into the F-holes, the result was a very natural appearance.

When mounting the piezo I put a few strips of Scotch 33+ electrical tape down where the pickup would be mounted. The 33+ can be removed without harming the finish.

I then put the piezo on the taped spot using some "putty" used for hanging posters on the wall. There are many sources for this putty, but I've found the blue or yellow types to be the best. The white type doesn't stick well enough.

I then covered the pickup with more electrical tape, and ran the piezo wire down the the bottom of the bass and then ran it behind the tailpiece where it was soldered to a 1/4" jack.

I can't tell you how great it worked. I used this many times over the years on violins in groups I've played with.

I have also used the same type of disk on acoustic guitars. On an acoustic guitar, I put the disk on the treble side of the bridge, on the clear area of the bridge.

This application sounds more natural than an under saddle pickup as it picks up from the top of the guitar as well as the strings.

I used to do sound at a regular "open mike" show at a popular coffee house. Most of the musicians performed with acoustic guitars but most did not have pickups. I made two of the pickup. As one performer played, I would stick a piezo on the bridge. Every player stepped on stage and would plug into a high impedance buffer I built.

It was so simple to deal with the flow of musicians that would play. No feedback problems and the guitar players didn't have to be intimidated by a mike and stand in front of them.

One key to any musical application of piezos is to plug them to a HIGH impedance input. One meg would be the minimum. I would suggest 5-10 meg ohms. Even an under saddle pickup will sound better when buffered by a very high impedance buffer/preamp. Much of the "quack" people don't like when using undersaddle piezos is the result of not using high enough impedance. Once the pickup is bufferec, a much fuller tone results. As you go down in impedance, less bass is produced.

I've used these pickup on all manner of acoustic instruments including guitars, upright basses, mandolins (pickup placed between the bridge and tailpiece), pianos and even a harp.

I worked on a rig for a musician that played harp near a waterfall in the Opryland hotel complex in Nashville. He played on a stage probably 40 feet off the ground in a beautiful "garden" in the hotel. The doors to the rooms surrounded this beautiful area.

The pickup system consisted of 3 piezos attached to the inside ...along the soundboard. We had one problem though. There was a terrible resonance around 250Hz. I found it was the pickup near the lower middle of the harp. We had one pickup near the top, one in the middle, and one in the bass area. The middle was the problem.

Rather than solve the problem with the mixer used for this system. I simply put a small capacitor in series with that piezo to roll off the low end. I think it was .0047uf, but this was many years ago. My memory isn't the best.

The piezos went into individual buffers, and then into a small, but nice mixer. He ran a monitor off the mixer, added some reverb, and sent a signal to the PA in this huge area. He had used mikes for years with inconsistent problems. This system simplified the amplification of his harp.

I don't remember his name, but he was billed as the "Liberace of the Harp." He dressed much like Elvis and even had a tall, black toupe. He was a magnificent musician.

Amplifying a piano had mixed results. Some pianos had just too much pedal noise.

I've been wanting to add piezos to my 5 string fretless bass. It has a Shaller Roller Bridge and I think it could be done with this bridge. I will try cutting up some piezo disks as was describled by an earlier poster.

These things are really fun. I put a Shadow piezo bridge on my main bass (a zebrawood, headless Explorer) back in 1983. They were incredible. I had to roll off the low end in order to make the piezo tone more compatible with the magnetic pickups.

I also had a headless Kramer. I tried putting a couple piezo disks on the underside of the bridge. They added an interesting, metallic tone with great high end and although the tone wasn't useful by itself, it sounded great when mixed with the magnetic pickups.

Our guitar player loved it and described the tone as "Scary!"

I have even had some success putting a piezo disk on the back of a speaker cone. No mikes needed.

FWIW. Barcus Berry actually made a VOCAL piezo pickup. It sounded great but the singers couldn't get used to the cable running out of their mouths.

I've built electronic drum pads that performed much better than the existing Simmons pads of the time.

Nice to find this site.
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Old 4th March 2005, 09:00 PM   #39
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Glad to read your reply here.

The mouth system you spoke up is triggering some ideas in my head. hmm... any more info on how this peice worked?

I found another spot on the headstock, that seemed to pick up sound pretty well too. just above the nut, on the back of the headstock. I had an old guitar that I cut a grove into the back of the neck and ran the wire into the neck and filled it so there is a lack of wire getting in the way.
I also seen those brass pieces they make to put on the headstocks to create more sustain. I was wondering about sandwiching it inbetween that, maybe it would change the tones some.

I have been debating on installing the piezo's on each string at the bridge and the nut. this should create some odd sounds. plus the notes on the other end of the strings.

I am looking at installing tons of piezos into a guitar, and giving them thier own on off switches, and see what kind of tones I can get out of it. what works, what doesn't. basically giving up a guitar to experiment on.

How do you go about boosting the high impedance input?
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