Actually he was demonstrating that it is the top of the guitar that is the important element. Also the papier-mache was not what we made in our early school life but more of a composite layup using hide glue (hide glue drys hard and crystalline).
I brought a pine b&s's cedar top guitar I made to a luther to critique and for a few minutes he did not notice it was pine ad only when I was talking about it he stopped playing and flipped over the guitar to look at the back.[/QUOTE]
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I agree with your points. As you hinted, different parts of a guitar top produce different sounds, as anyone can quickly tell by moving your ear (or a microphone) over the top of a guitar while it is being played.
To my ears, the brightest treble is usually found very near the treble end of the bridge, while the warmest bass tends to be well away from the bridge, somewhere on the lower bout (bigger half), and usually on the same side as the bass strings. Neither one by itself is particularly musical; one is too bright and "zingy", the other too dull and boomy.
Interestingly, there is an aftermarket piezo pickup with a reputation for producing relatively good sound. This one consists of three of those 50-cent circular piezos usually found in buzzers, beepers, and musical greeting cards.
The three piezos are glued to three locations underneath the top of the guitar. The wiring harness then parallels these three piezos. There is no electronics, making this a rather crude and entirely passive pick-up system.
The combined output of the three piezos is the sum of the acoustical output from three points on the vibrating guitar top. That's better than a single piezo right under the string saddle, though not as good as a microphone picking up the sound of the entire guitar body.
The original version of this pickup was quite expensive (I have forgotten the brand name and price, but I think it was priced in the range of $150 USD.) However, since this is a super-simple design, it was easy to copy. I now see very inexpensive Chinese-made clones available, such as this one: Amazon.com: Self-adhesive Pickups Piezo Transducer with 6PCS Celluloid Guitar Picks, 3 in 1 Microphone Contact & Endpin Jack 1/4" for Electronic Acoustic Guitar Violin Ukulele: Musical Instruments
I should add that I have not tried this type of pickup myself - I'm only repeating what I read in user reviews of the expensive original brand.
An additional bonus of this type of transducer is that it has much higher self-capacitance, and therefore much lower output impedance, than a typical undersaddle passive piezo sensor. This means you no longer need a super-high 10 meg input impedance - the three-piezo pickup is quite happy feeding a standard 1 meg guitar amp input impedance.
Every now and then I daydream about getting an acceptable plugged-in acoustic guitar sound out of one of my solid-body guitars. Putting my ear up against the solid wood body of my cheap Epiphone Les Paul SP II, I can hear an acceptably acoustic sound in a few locations, and I expect combining a few of those might produce even better sound.
I suspect a few well-placed piezo discs might actually generate an acceptable kinda-sorta-acoustic-guitar sound. Certainly it would be hard to sound worse than some contemporary Ovation guitars.
One of my friends has a 50 year old Ovation, which sounds fairly bad (but was acceptable in 1970, when plugged-in acoustic guitars were a new idea.) She also had a new (few years old) Ovation, which sounded utterly horrible, much, much worse than the old one.
The new Ovation sounded exactly like what it actually is: a chunk of cheap plastic with a harsh piezo pickup on it, as though you had mounted a piezo on a plastic bucket. Unbelievably bad. No self-respecting guitar manufacturer should ever sell something that sounds this bad.
My friend has loved her old Ovation for forty years, so it took months of bad tone before she finally allowed herself to realize that the new Ovation sounded awful. When she did, to her credit, she traded it for a big shiny Gretsch acoustic flat-top, which sounds hugely better. It also "sits in a mix" much better with her voice.
-Gnobuddy
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Thanks for the links!
The K&K Pure Mini is the one I was trying to remember earlier (3 piezo discs.) A hundred and forty-two bucks (American) for an endpin jack, three fifty-cent piezos, and a few feet of coax cable. Oh, also some silicone goo on the piezos to dampen unwanted resonances.
The James May Ultra Tonic with its five piezo discs is new to me, but it looks like a logical extension to the K & K Pure Mini concept. I would guess five properly placed piezo discs will probably get close to the limits of what is possible with this approach. I can't imagine it being worth the headaches to increase that to even more piezo discs and cables.
(I do suspect that a tiny mixer with trimpots to set the balance between piezos would be a worthwhile improvement. Even a passive one made with a bunch of 1 meg trimpots might do the trick, and be small enough to fit inside the guitar.)
Many months ago I noticed Digikey sells piezo bimorph discs like this in various sizes, and they are very inexpensive ( Buzzer Elements, Piezo Benders | Audio Products | DigiKey ). The next time I placed an order, I bought a few piezos in different sizes.
The plan was to try the small ones first, as they have their lowest fundamental resonance up around 6 KHz, above the entire guitar range. This means they should have a flat response through the actual guitar range, with nasty peaks high enough in frequency to have minimal effect on the sound.
Some of the big discs have strong peaks within the guitar's range of frequencies, and I would think these are best avoided, or placed on the guitar body in locations where there is very little treble to excite those nasty peaks.
Unfortunately I got distracted by several other shiny objects since buying those piezos, so they are still sitting in the junk box.
-Gnobuddy
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Those might have been the types we had for testing. Your idea off placing them on/in a les paul type for acoustic-like sound might just work great. I have to say i dont think all ovations sounds bad. I actually have cheapish Celebrity by Ovation that sounds quite good (not awesome)both acousticly and from its build in piezo with no Eq
The thing about the Ultratonic is that the four discs are in phase and the bass one is out of phase. The balancing board reduces the amount of out of phase signal by switching in capacitors rather than a trim pot as the piezo acts electrically as a capacitor. So the board and the 12 dip switches acts as a stepped attenuator. The other discs are just paralleled up at the board. I am guessing he buys the piezos, makes sense to buy the piezos cabled from China rather than messing around with it yourself and if they were just jumpered at the discs the user might break a wire in installation. The PDF in the installation instructions has a high rez picture of the board that can be blown up to see what is going on.
That would be nice! The guitar I mentioned, an inexpensive Epiphone Les Paul SP II ( Epiphone Les Paul Special II - Ebony - Long & McQuade Musical Instruments ) has a body that's much thinner than a real Les Paul. It also has no maple cap. The body is just a slab of some inexpensive wood. I think mine is all mahogany, while current ones have a basswood body and mahogany neck.
So the body of one of these is considerably more "live" than a proper Les Paul, with its thick body and stiff maple cap. I think that gives it a chance of sounding a bit more like an acoustic guitar once a few piezos are installed on it. The tricky part being where to put the piezos, and how to avoid ruining the guitar's appearance in the process!
I know Ovations captured most of the acoustic singer/songwriter market at one time in American history circa late 1960s/early 1970s.
Personally, I suspect that initial surge of popularity had almost everything to do with the fact that Glen Campbell, at the peak of his popularity, was seen playing an Ovation. With its thin neck and low action, it allowed Campbell to display his fantastic guitar technique and blazing picking speed. The fact that it didn't sound much like any kind of guitar was probably secondary to him at that point.
There has been a long slow decline in Ovation sales since then, and in recent years the company has been sold, taken apart, re-sold, put back together, all in the attempt to find enough customers to keep it going.
To me, the cheapest Yamaha acoustic guitar sounds better than the most expensive Ovation I've ever heard. Add the tendency for Ovation tops to tear apart over time, and the slippery and uncomfortable body, and I find I have no love for the brand.
The new breed of carbon-fibre guitars (Rainsong, etc) has finally demonstrated that you can actually make a guitar that sounds like a guitar out of entirely synthetic materials. But it seems to have taken forty-odd years to get from Ovation to Rainsong.
-Gnobuddy
I have thought about this possibility. It would certainly be the easiest way. Maybe the sound will be acceptable in this location.
A while ago I tried placing my ear against the body in various locations while plucking the strings, and the places where I liked the sound most, are nowhere near the rear access plate. That figures, Murphy's Law strikes again!
-Gnobuddy
To my ear, the tone near the bridge posts is bright and glassy, with lots of treble and very little bass or "woody" tone.
The tone was much warmer and more balanced elsewhere on the body. But I suppose if there are several piezos sampling several body locations, bright and glassy might be okay for one of them, as long as it's balanced by warm and bassy from another piezo.
In a Les Paul type guitar, the area near the bridge posts and the posts that retain the tailpiece is under very heavy mechanical stress from the tension of the strings. This might not be the best place to hollow out the wood too much. Perhaps very shallow routs on the underside of the body would be okay.
In my experience, these piezos produce prodigious amounts of output, almost regardless of what you do with them, or how you mount them. Piezo-ceramics are amazing materials, and generate plenty of voltage for even tiny or ill-chosen deformations.
You can actually get piezos to put out several thousand volts (!) in response to a sharp blow - my mom had a gas-stove igniter that worked like this.
But I think this is another interesting thing to investigate - what is the best way to mount the piezo, and in which orientation?
These disc piezos are usually "bender bimorphs", meaning their tendency is to form a shallow bowl shape when you apply a voltage between the two sides. This turns them into nice little loudspeakers / buzzers / beepers when you apply an AC voltage, with the centre of the disc vibrating back and forth in a direction perpendicular to the disc itself. Of course this is exactly the application the designers had in mind.
Reversing that, I found they produce a nice electrical output if you rigidly support the entire edge of the disc, leaving the centre unsupported, and then accelerate / vibrate the disc perpendicular to its face. The inertia of the piezo itself causes it to form a very shallow bowl / dome as it vibrates back and forth, which is exactly the shape it is designed for, so this produces a nice clean electrical output.
So it seems the proper way to use one of these discs is to glue a thin ring of something hard (metal, or hard plastic) to one side, with the outer diameter of the ring the same diameter as the piezo. Then you glue the other face of the ring to the guitar, so the piezo is spaced off the guitar by the thickness of the ring, and it's centre is free to bow very slightly up or down. A pinhole to release trapped air under the piezo and keep it from turning into a barometer (!) is a good idea.
A long time ago, I mounted a piezo in this way to the top end of the voice coil former of a powerful woofer, and turned it into a motional-feedback woofer. The piezo worked as an excellent one-axis accelerometer.
I have never seen this mounting approach taken with guitar piezos, though. The big guitar manufacturers (Yamaha, Takamine, etc) probably use piezos that are polarized in the proper direction for their own sensor designs. But for us DIY types who have to use off-the-shelf bender discs, it isn't a bad idea to be aware of the way these discs are designed to deform, and to use them accordingly.
-Gnobuddy
I just read the Tonedexter ad copy, and listened to this demo video. It seems like a nice product, though its price at $400 USD is enough to buy an entire guitar with. A nice guitar, at that.
Reading between the nearly information-free ad copy, my guess is the Tonedexter is basically taking simultaneous FFTs (Fourier transforms) of the microphone and piezo signals, and subtracting one from the other, which gives you the EQ curve needed to make the piezo signal sound like the microphone signal.
It is a clever idea, and one I used nearly twenty years ago to try to make a not-quite-anechoic room have the same frequency response as a proper anechoic room. Back then, it took an entire PC running Matlab to work out the correction filter. Now, it's done in a cheap little microprocessor inside the Tonedexter. Quite nifty!
Now, can we could do on our home PC what the Tonedexter does, and then design an active filter to produce more-or-less the proper EQ curve for that particular guitar?
It would be a lot slower process, and have to be done manually, one step at a time. But, in principle, I can't think of a good reason why it can't be done. Just start with simultaneous recordings made from both piezo pickup and a proper microphone, and then work with those WAV files on a PC to find their individual Fourier transforms, and then calculate the difference between them.
Software like Matlab (expensive) or Gnu Octave (free, open source, does many things that Matlab does) is probably all that's needed.
The technically hardest part would be designing a filter to recreate the EQ curve that comes out of the measurements. There may be a way to do a simple end-run around this: simply use a 31-band rack-mount graphic EQ. The dbx 231S is $200 USD, brand new (half the price of a Tonedexter.) I've found older dbx models for half that on Craigslist in the past.
-Gnobuddy
The idea of easily transforming anything nasty into something nice always makes me skeptical.
I do not expect this will work perfectly. My ears don't think the Tonedexter demo shows a perfect outcome, either. But I expect that some improvement to the piezo sound may be possible. I think the only way to find out for certain, is to try it.
The Fourier transform is a linear transform. As long as piezo and guitar body / microphone are linear (output voltage is directly proportional to string amplitude), fixed EQ can transform one into the other.
But if there is anything nonlinear in either response (such as an undersaddle piezo buzzing inside its wooden slot, or a vintage condenser mic with a distorting vacuum tube preamp, or a clipping opamp stage), then the Fourier transform cannot turn one signal into the other.
I have used Python, Scipy, and Numpy a little, but I am still at the beginning of the learning curve with all three.btw nowadays there exist powerful and free math-tools besides matlab. Have a look at numpy from the python world.
The trouble is that there are too many interesting things to learn in this world, and we only have one short lifetime in which to do it.
-Gnobuddy
I agree with you.
For a while I had a cheap electro-acoustic guitar sold by Walmart (!!). I bought mine for just over $100 USD back in 2009, while the same model now sells for $175 USD: https://www.walmart.com/ip/Kona-KA4...h-Solid-Spruce-Top-In-Natural-Finish/42753444
That cheap Walmart guitar had a plywood top, the worst tuners (tuning gears) I have ever encountered, and a bridge that was mis-aligned from the neck by about 5 mm sideways. The onboard piezo put out a thin sound badly lacking bass. Acoustic output was almost equally and lacking in bass. The thin body and plywood top made for a quiet guitar, lacking loud output.
But once I EQ'd the piezo signal and plugged it into a good amp, it sounded really quite good. It needed a lot of bass boost, some cut below 80 Hz to reduce thumping sounds, and a little cut to high treble. With that done, plugged in, it sounded about as good as any of the expensive Taylor / Martin /Gibson electro-acoustic guitars (also plugged in.)
The plugged-in sound was good enough that I fixed the other problems myself, and that was my only acoustic guitar for several years.
I now have a wide-neck Takamine guitar with their own Palathetic (TM) piezo pickup ( Takamine Guitars :: Palathetic Pickup ), and onboard "cool tube" preamp that uses a 12AU7. Whether or not the tube is a gimmick, I don't know - but plugged in, this guitar has much less of that harsh piezo sound than most similar guitars.
So EQ and/or nonlinear tube distortion can warm up and beautify a piezo signal. So can good piezo sensor design.
But my friends horrible new Ovation? I tried hard to make that #@#%^ sound better, and failed completely. Plugged in or acoustic, it sounded like beating on a broken plastic bucket. Just awful.
-Gnobuddy
I tried to think of a good use for that Ovation, I really did. Maybe to beat off an attacking moose? (We're in Canada, after all. And Ovations are famous for their durability, aren't they?)
Fortunately, the owner of that particular Ovation eventually realized that the bad sound was caused by the guitar, and traded it in. Like a true musician, she let her ears tell her the truth, even though what they told her contradicted long-held beliefs. I'm proud of her for doing that.
She still has her fifty-year-old Ovation. That guitar has shared some forty years of music-making with her, so I fully understand her loyalty to it.
-Gnobuddy
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