Abstract
Studies to find alternative low environmental-impact materials for
acoustic absorbers are still progressing, particularly those originated
from natural materials. However, most of the established works are mainly
focused on the fibrous-type absorbers. Discussion on the non-fibrous-type
absorbers is still lacking and this therefore becomes the objective of
this paper. Use of bamboo by utilizing its hollow structure to absorb
sound energy is discussed here. The normal incidence absorption
coefficient was measured based on the length and diameter of the bamboo,
as well as different arrangement of the bamboo structure subjected to the
incidence sound, namely, axial, transverse, and crossed-transverse
arrangements. The trend of absorption coefficient appears in peaks and
dips at equally spacing frequencies. For all arrangements the peak of
absorption can reach above 0.8. Introducing an air gap behind the bamboo
shifts the peak absorption to lower frequency. Covering the front surface
of the absorber improves the sound absorption coefficient for axial
arrangement by widening the frequency range of absorption also towards
lower frequency range. The transverse arrangement is found to have average
absorption coefficient peaks of 0.7 above 1.5 kHz. By arranging the bamboo
structure with crossed-transverse arrangement, the suppressed absorption
peaks in normal transverse arrangement can be recovered.
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