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Battery-Powered Instrument Amplifiers

Battery-Powered Instrument Amplifiers

by Joseph Ennis

Originally published in American Lutherie #69, 2002 and Big Red Book of American Lutherie Volume Six, 2013

After reading Francis Kosheleff’s description of building speaker enclosures which resemble instrument bodies, I thought I would offer my experience of what has worked for me. I have added battery-powered amplifiers and speakers inside instrument bodies to either augment the sound of a weak instrument like a harp or mandolin, or just to act as stage monitors.

The thing left unspoken in Mr. Kosheleff’s article is that not just any speaker will work well. The speaker should be chosen to match the instrument body resonance. The first air resonance of a hollow body instrument is essentially the same as the Helmholtz resonance of a tuned speaker cabinet. The same math applies. The formula is given below.

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