Tuned
idiophones (struck instruments) such as marimbas, vibraphones, xylophones, glockenspiels
chimes and bells have undergone centuries of development, resulting in complex
profiles, the purpose of which is usually to optimise the sound of the strike. When
building a tuned percussion instrument, there are certain aspects to be
considered which will affect the design.
1. TUNING
The
difficulty lies in tuning
the instrument. The designer seeks to produce an
instrument that responds with sounds that are pleasing to the ear, and for the most part this means that normal modes of
vibration are appropriately tuned. The many modes of vibration in bar affect
the sound it produces and give it its distinctive quality; however a strong
fundamental is essential for a good tone.
In the case of a xylophone or marimba bar,
it is the undercut that is used to tune the appropriate vibrational modes (Figure 1). Removing
material from any point on a bar affects all the modal frequencies to some
extent. The exact dimensions of the undercut are an
empirical design.
2. RESONATOR (Marimba & Vibraphone)
The purpose
of the resonator is to amplify the fundamental frequency produced by the bar
and also to increase the loudness, which is done at the expense of shortening
the decay time of the sound. This becomes increasingly important as
the frequency extends lower and the radiation power of the bar becomes weaker.
References:
Vienna Symphonic Library.
“A comparison between four mallet instruments.”
2002; accessed 30 June 2012
Flynt, W.E. “The Construction and Tuning of
Vibrating Bars.” Mechanical Music Digest
V1 (Jan 2009), 51-53.
Legge, K.A and J. Petrolito. “Designing Idiophones with Tuned Overtones.” Acoustics Australia
V35 (Aug 2007), 2-47.
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