Russell C. Coile
Parabolic Sound Concentrators
By R. C. Coile, Journal Of The Society of Motion Picture Engineers,
Volume 51, September, 1948, Washington, D. C.
Parabolic sound concentrators have long been investigated for
application to military antiaircraft location, radio broadcasting, and motion
picture recording. Olson and Wolff, of the Radio Corporation of America,
developed a combination horn-refl ector concentrator in 1929. Obata and
Yosida, of Tokyo University, published measurements of amplifi cation in
1930. Hanson, of the National Broadcasting Company, described the use
of parabolic refl ectors in broadcasting in 1931. Dreher reported in 1931
on the use of microphone concentrators in motion picture production.
Sato and Sasao published the results of tests on the sound fi elds of deep
parabolic refl ectors in 1932.
Rocard published an analysis of the theory of the amplifi cation of the
refl ector-type parabola in 1932. Schneider of the Moscow Radio Center
made amplifi cation and directivity measurements in 1935 while studying
the application of parabolic concentrators to Russian broadcasting and
checked his amplifi cation data with Rocard's theory. Gutin, in Leningrad,
independently derived the theory of amplifi cation and went on to analyze
directivity in 1935.
This paper presents the pertinent historical background and reports
on an experimental verifi cation of the theoretical acoustical directivity of
parabolic concentrators as well as further checks of the amplifi cation theory.
The sound fi elds inside parabolic refl ectors have also been investigated
experimentally with an agreement found with theoretical fi elds calculated
by principles of geometrical optics.
The idea of using a parabolic mirror as a concentrator of sound by
placing one's ear or a microphone at the focus was a subject of research
in World War I. Waetzmann
has described German parabolas and Tucker
has reported on English and French development of plaster and concrete
parabolic refl ectors. The only quantitative data given in these reports is an