Obliquely Truncated Simple Horns: Idealized Models for Vertebrate Pinnae
Date
1988
Authors
Fletcher, Neville H.
Thwaites, Suszanne
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Publisher
European Acoustics Association
Abstract
The acoustical behaV:iour of simple horns of parabolic, conical and exponential profile is analyzed
and explicit expressions are given for the impedance coefficients Zii. Wavefront curvature effects are
included and the discussion is extended to investigate the effect of oblique truncation, which gives
the horn a shape closely similar to that of a typical vertebrate pinna. The effects of higher modes.are
discussed qualitatively and the conditions under which these can be neglected are outlined. All
horns are shown to act as efficient pressure transformers over only a restricted bandwidth, the limits
of which are determined by flare rate and mouth diameter. For a horn with throat area S1 and
mouth area S2 the maximum blocked-throat pressure gain is 10log10 (4 S2/S1) decibels; the gain
reduces to 0 dB _at low frequencies and may become negative at very high frequencies. Oblique
truncation raises the maximum gain above that of a horn truncated normally with the same
minimum throat-to-mouth distance. It also moves the axis of maximum acoustic response away
from the geometric axis of the horn towards the normal to the oblique mouth. This shift is large at
low frequencies, becomes slightly nega;pefe at mid frequencies, and approaches zero at high frequencies.
Use of these results .in the analysis of model auditory systems is outlined.
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Acta Acustica united with Acustica
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Journal article
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Open Access
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