Mode frequency and damping changes due to chemical treatments of the violin bridge

Abstract

Hammer‐impact modal analysis using a microphone as a no‐load vibration transducer was performed on violin bridge blanks chemically treated two different ways to extract free–free vibrational mode frequencies, dampings and shapes for comparison with untreated bridges. Data were taken for both in‐plane (IP) and out‐of‐plane (OP) vibrations over a 0–20 kHz range. Average effects of these chemical treatments on mode frequency and damping were determined from IP and OP single‐point excitation on six Formalization (FA), six Resorcin/formaldehyde (RE) bridges, and eight untreated (UN) maple violin bridge blanks. All the bridges exhibited three well‐defined IP modes and six OP modes. Few significant changes were observed between the frequency and damping parameters of the IP and OP mode shapes, although the RE treated bridge exhibited a possibly unique doublet at ∼9 kHz. Since no mode frequency variations ≳1.5% were found, even though the RE treatment increased bridge masses 9.1%, it was concluded that the combined mass/stiffness changes of the wood were related to the acoustic effects observed with these bridges [H. Yano and K. Minato, 1222–1227 (1992)].