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Tone bars - image courtesy of Harlan Mandolins
Tone bars are pieces of spruce (or occasionally other wood, or composite/laminate) that are glued to the underside of a mandolin top (or mandolin family top, or archtop guitar top).
They are made from vertical grained stock, and are glued in the lengthwise direction of the top. They are often referred to as parallel braces, but are seldom truly parallel. Instead, they are usually splayed wider toward the tail end on the instrument.
Statically, tone bars function as beams to distribute the downward pressure of the strings on the bridge throughout the top, and dynamically, to influence the frequency of top plate vibrational modes.
Authored by: John Hamlett
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