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### How Do I Build an Electro Magnet Strong Enough to Vibrate Piano Strings?

05/28/2012 1:29 PM

I would like to build an electro magnet capable of causing piano strings to vibrate without the strings being struck first. As long as the hammers are up, the strings would vibrate on their own accord. An E-bow, used by guitarist for the same purpose, will (sort of) work on a limited range on the piano - but on only one note at a time. I would like to build something that can be hung inside the piano, close to the strings, that covers a wide range of notes. Hopefully I would be able to silently depress the keys, lifting hammers on those keys only, and thus creating an infinitely sustained piano sound, but without the attack the hammer gives. Thanks!

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#1

### Re: How Do I Build an Electro Magnet Strong Enough to Vibrate Piano Strings?

05/28/2012 2:18 PM

You are probably aware that each string is actually 3 wires spaced about 0.15 inches apart. Each hammer actually hits 3 wires simultaneously. So you'll need a field that is fairly uniform over a width of about 0.3 to 0.4 inches, for each note.

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#2

### Re: How Do I Build an Electro Magnet Strong Enough to Vibrate Piano Strings?

05/28/2012 2:20 PM

I can't say that I am familar with piano wire or piano wire installation.

A question for you though: Does the installation of piano wire allow you to connect a lead to each of the wires (one at each end) overwhich an electrical current could be introduced?

If this is true, then perhaps a magnetic field could be set up in individual wires to the strength necessary to quickly move it towards a small electro-magnet placed over the wires.

This could be an interesting project to pursue.

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#18

### Re: How Do I Build an Electro Magnet Strong Enough to Vibrate Piano Strings?

05/29/2012 10:37 AM

Not in a piano where it has a metal frame - like most of the modern ones do.

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#3

### Re: How Do I Build an Electro Magnet Strong Enough to Vibrate Piano Strings?

05/28/2012 2:30 PM

The field from each electromagnet would have to be oscillating with a frequency very close to the resonant frequency of the corrsponding string to get this effect. It could either be done by excitation oscillators (one for each string) or using feedback (which would give an even slower attack than the former method).

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#4

### Re: How Do I Build an Electro Magnet Strong Enough to Vibrate Piano Strings?

05/28/2012 2:50 PM

In line with Usbport's observation, I would think of experimenting with a rectangular soft iron core about 3/8" x 3/4" (10mm x 20mm). One end of this rod would be close to the string group; the other end would have a coil of copper wire of gauge suited to the combination of voltage and current, which may need some experimentation.

The hammers do not normally contact the strings, but the dampers do; and they are what you need to lift. The damper pedal lifts all; a real sostenuto pedal maintains the lift of any that are up when the pedal is pressed. Each piano key lifts the damper for its strings, but lowers it again when the key is released. Maybe some combination of these could do what you want, but I suspect you need something further.

If the electromagnet is intended to sustain a long note, rather than just initiate it, it may need to be energized by AC to match the frequency of the note, or a divisor of it.

Very interesting challenge--please keep us posted on how it works out!

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#5

### Re: How Do I Build an Electro Magnet Strong Enough to Vibrate Piano Strings?

05/28/2012 3:12 PM

Perhaps it's a difference in terminology. In my piano a small felt-headed hammer strikes each set of strings. I can see this action when I lift the piano lid and press a key.

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#6

### Re: How Do I Build an Electro Magnet Strong Enough to Vibrate Piano Strings?

05/28/2012 3:51 PM

The dampers are harder to see, being typically below/behind the hammer mechanism. There are variations depending on grand/upright/spinet piano construction, in particular for the piano (soft) and sostenuto pedal actions. The damper pedal is easy; it just lifts them all.

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#7

### Re: How Do I Build an Electro Magnet Strong Enough to Vibrate Piano Strings?

05/28/2012 4:06 PM

Hello everyone - thank you for all for responding so quickly to my query. I have no knowledge in these areas (I'm a composer), but I can sort of follow along with what everyone is saying. If I can ask a few follow up questions... 1) How to I create/buy an excitation oscillator? 2) Where can I go to learn about controlling AC, in case I want to build something that matches the frequencies of the different notes? Piano frequencies are easy enough to calculate that even I can do it, and being able to control the current to each string would let me create uniform attack/sustain across the keyboard. While I'm sure even my questions are full of errors, I appreciate getting help from experts! I think what I really need is an eager grad student to give me hands on advice...

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#9

### Re: How Do I Build an Electro Magnet Strong Enough to Vibrate Piano Strings?

05/28/2012 5:10 PM

It might be valuable for you to hook up with a piano tuner/reconditioner, who can give pointers on how the actions work and where to have the electromagnets interact with the strings. Solar Eagle's intervening post (GA) looks worth following up, too.

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#17

### Re: How Do I Build an Electro Magnet Strong Enough to Vibrate Piano Strings?

05/29/2012 10:36 AM

You may want to start by getting an Arduino and an audio shield. A shield is another board that plugs on top of the Arduino.

The Arduino is easy easy easy to write code for, and it is very versitile. It will make what ever you do to drive coils over wires or motors or whatever easy to setup and test.

I am currently working on a "coil" project that will use an Arduino and Audio shield to drive the coil and the arduino has made the project more about building the coil than controlling it. I don't have to sweat the control part!

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#8

### Re: How Do I Build an Electro Magnet Strong Enough to Vibrate Piano Strings?

05/28/2012 4:19 PM

It's been done...

"By positioning a rack of transducers above the piano's strings - but never in physical contact with the strings - electromagnetic waves in the air gap create vibrations and sound from each of the piano's many naturally oscillating strips of steel. These transducers, a combination of electromagnets and permanent magnets, all connect to the soundcard output of a personal computer, where audio output signals can specified through any arbitrary software interface. The net effect, captivating as both a sound and an idea, is the ability to play the piano without felt hammers, plectrum, fingers, or any other traditional method of physical excitation. Notes can simply be played from the keyboard of a laptop."

"As with other piano preparations, the range of sounds available to the pianist in some ways resemble the sound of the unprepared piano e forte, and in other ways is quite divergent. For example, by sending a sine wave signal from a computer to the A4 string (440 Hz), the string will vibrate at this naturally resonant frequency. A sustained tone will eminate as long as the electrical signal endures, and will be shaped by the contours of the piano string and body, in a manner analogous to filtering. What is especially exciting about this method of vibrating the string is the ability to send virtually any sound wave into a string. In the previous example, one could send another sine wave into the same A4 string, but at a frequency of 880 Hz. The resultant tone will then be an octave higher than that heard from pressing the A4 piano key normally. Having the option to isolate partials on each string and combine them in different ways opens up new pathways to timbral expression previously available to the pianist in some degree, but typically regarded as a synthesis method of the electronic musician. One might call this speakerless acousmatic synthesis. The most recent incarnation of the instrument consists of twelve independent channels (i.e. twelve transducers over twelve different notes). When played in combination, the instrument bears striking resemblence to a church organ, but with strings!"

https://ccrma.stanford.edu/~sbacker/empp/what.html

What's it sound like? Here's some idea...

http://vimeo.com/26595061

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#10

### Re: How Do I Build an Electro Magnet Strong Enough to Vibrate Piano Strings?

05/28/2012 7:55 PM

If not hitting the strings, would this be a single excitation or continuous? If continuous, would you not have to excite each one at it's natural frequency? Why not use a programmable electronic keyboard? Or am I missing something.

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#11

### Re: How Do I Build an Electro Magnet Strong Enough to Vibrate Piano Strings?

05/29/2012 12:08 AM

I salute your ambition, but wonder what you will gain if you are only able to excite 10 strings at a time.

The response you will attian with electromagnets will not be as crisp as a hammer strike and you will find it challenging to control the pitch/sustain electronically with the foot pedals.

Not impossible, but a challenge.

It seems to me you won't have a piano any more.

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#12

### Re: How Do I Build an Electro Magnet Strong Enough to Vibrate Piano Strings?

05/29/2012 3:20 AM

Wouldn't it be easier to borrow a Claviona <usual disclaimer>?

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#13

### Re: How Do I Build an Electro Magnet Strong Enough to Vibrate Piano Strings?

05/29/2012 7:29 AM

Maybe a look at this gentleman's work may help.

http://en.wikipedia.org/wiki/Robert_Moog

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#14

### Re: How Do I Build an Electro Magnet Strong Enough to Vibrate Piano Strings?

05/29/2012 8:49 AM

I haven't seen this done with a piano but i have with a violin. Rather than exciting the strings in the manner you are suggesting each of the violin strings had a small rotating wheel above it which would push down onto the string. Have a look at the Paul Corin museum site for details. Corin runs a mechanical music museum.

Someone has already pointed out that the piano strings are in groups of 1, 2 and 3 dependant on pitch - the groups of 3 being the higher frequency.

Is this what you are trying to do:

http://music.ece.drexel.edu/research/mrp

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#15

### Re: How Do I Build an Electro Magnet Strong Enough to Vibrate Piano Strings?

05/29/2012 9:27 AM

I got a picture of a system where in the anchors for the strings have an 'excitable' component. Imagine a solenoid attached at right angles to the point(s) where the strings are attached. The strings would not get 'touched' but the end(s) of the string would 'vibrate'. I don't think the 'solenoid' would have to be triggered but one time to create the desired vibration on the string. The strength of impulse (power) to the solenoid could be regulated according to a computerized program &/or stress sensors in the piano keys themselves. String dampers would operate as normally. This would sidestep the issue of creating a new technology specifically for affecting piano strings (in a manner commentary seems to be examining). Carlos, My Dad's son.

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#16

### Re: How Do I Build an Electro Magnet Strong Enough to Vibrate Piano Strings?

05/29/2012 10:33 AM

Again, thanks to everyone for posting. There are lots of great ideas. Both the links posted by SolarEagle and silverfox are close to what I have been imagining. It's very helpful, so thanks for sharing! I don't mind not being the first to have this idea :)

As for the doubters, of course similar sounds can be synthesized, but most pianists and composers will always want the real thing. Producing these beautiful sounds from an acoustic piano has a certain "something" that a traditional synth just won't be able to replicate. Check out the links and you'll see what I mean!

I'm meeting with something today who has some solutions as well. I will keep this thread posted with developments!

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#19

### Re: How Do I Build an Electro Magnet Strong Enough to Vibrate Piano Strings?

05/29/2012 10:38 AM

If you had a coil and an amplifier circuit for each set of strings (88 in all) , you might be able to set up positive feedback if the strings are steel. (I think they are, check to see with a magnet.) The circuit would favor whatever harmonics had a anti-node (maximum movement) at the position of the coil. I would assume you would put the coil at the hammer point, to get the same timbre as the piano sound. The attack portion of the sound envelope may be more gradual than you want, but if it works, it should build up to a sustained level.

It might be an interesting project to try with one string set before you make any big investment.

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#20

### Re: How Do I Build an Electro Magnet Strong Enough to Vibrate Piano Strings?

05/29/2012 10:59 AM

The piano strings don't just vibrate freely - you have a damping action on it. Pressing the right pedal moves the felt pads away and the left pedal pushes the felts on harder.

If you play a piano with the right pedal pressed you will just end up with a mush of sound.

Getting a string to sound is an aggressive action with a hammer (it is a percussive instrument) so you might find the gentle vibrating action will be a massive disappointment.

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#21

### Re: How Do I Build an Electro Magnet Strong Enough to Vibrate Piano Strings?

05/29/2012 1:20 PM

The preceding discussion was interesting, and covered a fair territory.

BUT

It left out two fundamentals:

1,. A tone in an instrument is defined as unique by its attack signature. The sustained part is not at all different. A hammer in a piano, a plucking in a clavichord or harp, a guitar, the attack of the bow on a violin is largely determining the perceived sound. An electromagnetic excitation provides none of it.

2,. The tone produced by a triplet of strings. They need to be off of each other to provide loud and quality sound from your piano. When I was unhappy with my tuner (a nice guy any other way), I learned tuning. Now, I can tune up a piano from honky tonk, to iazz, to Bach recital. Fair, not nearly professional quality, not one tenth their speed. But can do on a yeoman level.

2.1,. On a technical level, every one of a tightly coupled triplet needs to be excited at its own, by coupling constantly modulated frequency to sound even approximately right. That is a filter electronic subspecialty.

3,. You do not need to believe me. Research it, then build a single triplet. And let us know your results.

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#22

### Re: How Do I Build an Electro Magnet Strong Enough to Vibrate Piano Strings?

05/29/2012 3:56 PM

Make the strings the coils.

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#23

### Re: How Do I Build an Electro Magnet Strong Enough to Vibrate Piano Strings?

05/30/2012 3:42 AM

In my opinion a good piano is one that is on fire. Being dropped from a high place can also help it.

Time to come off the fence with this piano non sense and start looking for an old Hammond B3. Now you can really do stuff with an old Hammond.

No other make though - make sure it has tone wheels.

Pianos - pah!

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#24

### Re: How Do I Build an Electro Magnet Strong Enough to Vibrate Piano Strings?

05/30/2012 10:02 PM

This is a positive note for our enterprising experimenter.

I would build the triplet on the edge of a 2x8 or 2x10 for stiffness, attaching a thin plywood as a sound board. The piano parts do not cost much.

I would mount the electromagnets on a slide. You may excite the strings at their fundamentals, 3rd, 5th, 7th etc harmonics that way.

Why not even harmonics? You tell us!!

Why does a piano crosses sets of strings? (think of nodes of resonances).

And a few more, that does not come to mind right now.

You can cover a fair portion of classical physics with a few experiment that way. Go for it, as you cannot go wrong.!

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