Letter: Beam Stiffness vs. Strength

by Fred T. Dickens

Originally published in American Lutherie #41, 1994



Dear Sir,

Please allow me to attempt a termination of the continuing misunderstandings originating with Mr. Ervin Somogyi’s interesting but flawed lecture given at the ’92 conference in South Dakota and perpetuated by its subsequent transcription in the GAL Journal and the letter in American Lutherie #39 from Mr. Dave Schwab commenting on the matter.

The issue has to do with using the terms “strength” and “stiffness” interchangeably when discussing the mechanical characteristics of beams used as braces in guitar sounding boards.

Both strength and stiffness of beams are important characteristics and depend on properties of the materials from which the beams are constructed as well as the physical dimensions of the beam. Both stiffness and strength of beams may be calculated using formulas which only require a knowledge of the material properties and physical dimensions. Those so inclined will find a very readable account of these formulas in Understanding Wood by R. Bruce Hoadley, ISBN 0-918804-05-01.