Percussion Instruments: Sustained versus Damped Sound
Name: Rue
Status: educator
Grade: 6-8
Location: NC
Country: USA
Date: Fall 2011
Question:
When studying percussion instruments, students discovered: (a) the sound of metallophone bars (metal bars similar to a vibraphone) is sustained and (b) the sound of xylophone bars (wooden bars) is not sustained. Students wanted to know why the metal bars have a "longer sound" than the wooden bars.
Replies:
Rue,
Metal is more elastic than wood. Consider a hard metal rod and a
hard wooden rod of the same shape and size. Bend each one a little
and the metal rod is more likely to go back to its original
shape. For the wooded bar, tiny bits and pieces of the wood
structure are damaged every time the bar bends. This uses up the
vibration energy quickly.
Dr. Ken Mellendorf
Physics Instructor
Illinois Central College
Because metals are very solid they transmit sound quickly and
efficiently. Wood on the other hand has air pockets and individual
fibers that move around and absorb energy very well as sound
passes. The wood eats up the energy of the strike in a thing called
internal resistance.
Hit one end of a 2X4 and the sound dies out over the length of the
wood. Sound can be heard in rail road rails over many miles.
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