<html><body><div style="font-size: 12pt; font-family: "times new roman", "new york", times, serif; color: rgb(0, 0, 0);"><div>I'd think a speaker is highly inductive. The coil is wound close to a magnetic core, it moves through a small gap. I don't know how much power you need, but an audio amplifier should certainly</div>
<div>handle that. Try winding a coil around some iron core and try it. It might be good to use something like the core material from an old transformer (laminated metal) or maybe a bunch of nails</div>
<div>bundled together. You could aim for an impedance in the 4-8ohm range. </div>
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<div>There is a commercial product called "sustainiac" which is in the form factor of a guitar pickup. For starters I'd play with just a single string and then refine it from there.</div>
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<div>Harry</div>
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<blockquote style="margin: 0 0 0 .8em; border-left: 1px #ccc solid; padding-left: 1em;"><hr id="MESSAGE_DATA_MARKER"><strong>From: </strong>Spiros <synth-diy@synth-diy.org><br><strong>To: </strong>synth-diy <synth-diy@synth-diy.org><br><strong>Date: </strong>Wednesday, 7 September 2022 2:02 PM EDT<br><strong>Subject: </strong>[sdiy] Magnetic String Actuation<br><br>
<div dir="ltr">Hello, list,
<div>I am interested in experimenting with magnetic string actuation. That is, use an electromagnet to induce vibration to metallic(?) strings; the opposite of what a guitar pickup does typically. I have seen this concept realised in a couple of different applications:</div>
<div>1. <a href="http://instrumentslab.org/research/mrp.html" target="_blank" rel="noopener noreferrer">Magnetic Resonator Piano</a> is an electronically augmented piano that can do cool stuff such as real crescendos, electromagnetically dump strings, produce overtones etc. Every sound produced comes from the strings themselves.</div>
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<div>2. <a href="https://www.thomann.de/gr/ebow_ebow.htm" target="_blank" rel="noopener noreferrer">Ebow</a> is an electromagnetic actuator for the electric guitar. Place it close to the strings and they will start vibrating, similar to the way they do when using a bow.</div>
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<div>3. <a href="https://www.soundonsound.com/reviews/moog-guitar" target="_blank" rel="noopener noreferrer">Moog Guitar</a> contains some sort of actuator and suitable circuitry to make it infinitely sustain notes, apply active damping and more.</div>
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<div>I bet there are more if we start digging, but these are some examples I can think of off the top of my head. Unfortunately, I don't have enough to go on here and decide on what kind of hardware I need to produce this effect. The magnetic resonator piano researchers have published a couple of papers that go over the fundamental equations involved. Still, unless you can really wrap your head around them (I can't) it's not enough to get you going.</div>
<div>I obviously need some electromagnet, either off the shelf or custom wound. Then I need an amplifier that can drive enough power into it, in the correct frequency range. </div>
<div>Aliexpress is full of various electromagnets. How could I decide on a couple that might be promising and give them a try? </div>
<div>What about output amplifiers? I know the basics of driving speaker coils, but my guess is a strongly inductive load like an electromagnet is going to be a different story.</div>
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<div>I've been thinking about this for the past 10 years and still didn't manage to figure it out. Any kind of info or advice you could share is invaluable!</div>
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