When you go by a handle like [Simplifier], you’ve made a mission statement about your projects: that you’ll take complex processes and boil them down to their essence. So tackling the rebuilding of the humble speaker, a device he himself admits is “both simplified and optimized already,” would seem a bit off-topic. But as it turns out, the principle of magnetostriction can make the lowly speaker even simpler.
Most of us are familiar with the operation of a speaker. A powerful magnet sits at the center of a coil of wire, which is attached to a thin diaphragm. Current passing through the coil builds a magnetic field that moves the diaphragm, creating sound waves. Magnetostriction, on the other hand, is the phenomenon whereby ferromagnetic materials change shape in a magnetic field. To take advantage of this, [Simplifier] wound a coil of fine copper wire around a paper form, through which a nickel
TIG electrode welding filler rod is passed. The nickel rod is anchored on one end and fixed to a thin brass disc on the other. Passing a current through the coil causes the rod to change length, vibrating the disc to make sound. Give it a listen in the video below; it sounds pretty good, and we love the old-time look of the turned oak handpiece and brass accouterments.
You may recall [Simplifier]’s recent attempt at a carbon rod microphone; while that worked well enough, it was unable to drive this earphone directly. If you need to understand a little more about magnetostriction, [Ben Krasnow] explained its use in anti-theft tags a couple of years back.