Machele Bailey
George Bissinger
Phys. Dept., East Carolina Univ., Greenville, NC 27858
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,