acoustics
[Film Technology]
Acoustics (Greek,
akouein, “to hear”), term
sometimes used for the science of sound in general. It is more commonly used
for the special branch of that science, architectural acoustics,
that deals with the construction of enclosed areas so as to enhance the hearing
of speech or music. The acoustics of buildings was an undeveloped aspect of the
study of sound until comparatively recent times. The Roman architect Marcus
Pollio, who lived during the 1st century BC,
made some pertinent observations on the subject and some astute guesses
concerning reverberation and sound interference. The scientific aspects of this subject, however, were first
thoroughly treated by the American physicist Joseph Henry in
1856 and more fully developed by the American physicist Wallace Sabine in
1900. Acoustics (theatre), the science of sound as
applied to theatrical performance. The astonishingly good acoustics of Greek amphitheatres such
as that at Epidaurus were developed by trial and error rather than detailed knowledge
of physics and mathematics. Indeed, the history of the application of
mathematics to the analysis of sound in an enclosed room is less than a century
old. The Boston Symphony Hall, built in 1901, was the first auditorium to benefit from the
analysis of acoustics by Wallace Clement
Sabine. Sabine pointed out that the
limited range of the spoken voice, compared to music, may explain in part why
theatre has been relatively ignored by acousticians, compared to concert halls.
The lack of attention paid to acoustic design and analysis of the theatre is
also due to the history and tradition of theatre building which, provided the
rules were followed, invariably ensured a successful natural acoustic.
Sabine formulated a key equation in acoustics that calculates the reverberation time of an
enclosure in the 1920s. Since then, there have been enormous developments in
acoustic theory, analysis, and measurement. The study of room acoustics is now
a complex, highly mathematical subject. Nevertheless, the essential requirement
is simple: that the choice of reverberation
time should be carefully selected to
suit the intended uses of the auditorium. Theatrical production has special
requirements in terms of acoustics. Unlike a seated orchestra, actors move
about a wide area, often speaking with their back to the listener. There are
also a number of sources of background sound that need to be controlled, in
addition to ensuring that the speech on stage is clearly audible—the noise of
modern and sophisticated lighting systems and mechanical plant, for
example.Modern theatres are invariably expected to be “multi-purpose auditoria”,
and have to accommodate anything from wrestling and string quartets to
rock music, making the specification of a single, optimum set of acoustic
requirements difficult. Another problem is size. Because of their large
proportions, these new auditoria rely on sound reinforcement systems.
These have evolved from the “assisted
resonance” system developed by Peter Parkin and
used to good effect in London's Royal
Festival Hall in the 1960s. The
challenge of the future lies in the possibility of using electro-acoustic reinforcement systems. The use of these remains controversial amongst actors and musicians, but
suitably subtle systems may prove to be acceptable to all.
ACOUSTIC RESONANCE
Can occur as the sound reverberates [reverberation] to and fro between parallel non-absorbent surfaces. Acoustic resonance can be
avoided by sound diffusion. This is usually
achieved by introducing deliberate irregularities in the surfaces involved.
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