> > > >

1948-49 Theatre Catalog, 7th Edition, Page 337 (324)

1948-49 Theatre Catalog, 7th Edition
1948-49 Theatre Catalog
1948-49 Theatre Catalog, 7th Edition, Page 337
Page 337

1948-49 Theatre Catalog, 7th Edition, Page 337

Space Acoustics

A General Discussion as Presented Before the Atlantic

Coast Section, SMPE, in New York 011 February 19, 1947

Sound is a form of pulsating or vibrating energy and in this discussion we are concerned with its behavior in an enclosure or restricted space. The be havior of sound energy in space, be it in a theatre, studio, living room or bathroom, i-s acoustics. The source of the sounds may be a vibrating string, membrane, column of air, or vocal chords. The air as a medium coupled to the source carries the vibration throughout the space until attenuated by distance, or absorbed by boundary surfaces.

Sustained sounds thus will fill a space and the intensity will grow by the addis tion of the various reflections until that steady state is reached when the energy of the source is balanced by the boundary loss, or absorption. If the source is suddenly stopped the residual sounds continue to reflect and to die away because of absorption.

The time taken for the sound level to drop 60 decibels is called the reverbera tion time. Some modern structures with l

hard surfaces have been known to have reverberation times in excess of 10 seconds. When we consider that we normally speak about three syllables per second and this extreme would mean thirty syllables running around the hall at the same time, we see what utter confusion and unintelligibility can result from excessive reverberation. Music in the same place would sound as though the loud pedal were on all of the time.

It is probable that the growth of modern music and our appreciation of it have been molded by the architecture of our buildings. The music of most primitive civilizations developed out of doors, as the homes of these early cultures were generally in tropic or semitropic climes. Their music has survived in the Near East and in the Orient largely in pentatonic and whole-note scales. Harmony as we know it cannot be obtained using these scales. They are best suited to heavy octave melodies, or staccato tunes for flute and strings built over the various drum rhythms.

An example of this use of ancient scales is in Japanese music today. Their traditional music is played out of doors, in shrines open at the sides, or in houses constructed of thin wood, bamboo, and paper so Himsy and absorbent as to simulate outdoor conditions. However, as the Japanese have gradually adopted the fireproof construction of the west, their modern music has likewise begun to make use of our scales and to take on the style of western music.

In the Christian era the march of civilization was toward the temperate zone of Europe. During the early centuries the church became the seat of culture and the main source of developing musical tastes. In the main, the churches,

JAMES Y. DUNBAR Johns-Manvillv Corp., New York, N. Y.

Summary-The relationship between the area, shape, and fitments of a sound studio or auditorium and their effect on sound quality is discussed. A probable evolution of music appreciation, from the pentatonic and whole-note scales of certain primitive peoples to harmony, as we know it today, is traced. Various methods of acoustical treatment of enclosed areas are described.

temples, and cathedrals were of much greater volume than other structures and they were enclosed against the more rigorous climate. Stone replaced wood as more enduring materials were used.

These factors aided in prolonging reverberation of sounds because reverberation depends on the amount of space enclosed and on the hardness of the surfaces. The notes overlapped. The more primitive scales when used in such places provided dissonances which were unpleasant to the ear. The Gregorian chants arose. The diatonic scale came into popular use, particularly in early operas. The hurdy-gurdy grew into a harpsichord, then into the piano and organ. Bach, Beethoven, Brahms, Stravinsky, Debussy, Ravel; changing scales, new instruments, great composerseand new architecture.

There are many of us who remember the early silent motion pictures where the sound effects consisted mainly of a piano and the quality of the music was of little value except to cover up the sound of the projection machine and to fill the time of changing reels and repairing film breaks. The legitimate theatres, concert halls, and churches inherently either had good or bad acoustics and little was done about it.

HAcoustics" was about as vague a term as politics, as little known and frequently as aimless. During this period miles of wire were strung up in auditoriums all over the country and some of it still exists. While it was one of the early attempts at acoustical treatment it is known that it did no good at all.

In the early part of this century Professor Wallace Clement Sabine of Harvard University put the acoustics of buildings on a scientific footing by establishing the relationship between reverberation time, room volume, and sound absorption.

llriginnlly presented Feb. I9. 1947. before [he Allunlic (Io-m Section of the Society of Molion Picture Engineers and published in [in S.M.I'.E. Journal, 01-1.. 1947

The subsequent treatment of many rooms and the use of articulation tests have determined that the optimum value of reverberation for a room is a function of its volume. Also, it was learned that a room used almost entirely for music should be somewhat more lively than one of the same volume intended primarily for speech.

As long as we depended mainly on the power of our own voices and musical instruments, most of our auditoriums were fairly satisfactory. The bad ones were usable even though they were annoying. But when the audion valve, vacuum tube, and triode came into being the course of the entire history of sound changed. We could then amplify the sounds we knew, thus putting many times the sound energy into the same enclosed space. In .this way the old acoustical defects were multiplied.

Sound came to us in the form of radio-receiving sets, public-address systems, and sound motion pictures. People accepted the deficiencies of these new forms of education and entertainment as long as the novelty remained. But soon they were complaining about the old halls that boomed and growled with reverberation and echoes. They Wanted something better. And as the sound industry improved acoustics had to improve with it.

We had had experiences in our homes with the sound-deadening eifects obtained by the use of heavy carpets, draperies, and similar materials; however, little was known of the very few commercial acoustical materials existing at that time. So the attempts to deaden the noisy rooms and halls were generally made with home furnishings.

Accordingly, upholstered seats, carpets, and acres of draperies made their sudden appearance. Draperies ranged through theatrical gauze to monk's cloth and heavy velour folds alone, or applied over all kinds of felts, jute, and cattle hair. Quilts, blankets, and rugs, too, were hung up in attempts to subdue the bouncing sounds.

The same unstudied treatment was given to early radio studios, recording studios, and sound stages. The pickup and recording equipment were just about as rough in those days as the rooms in which they were used, and the noisy scratch of early synchronized films would make poor entertainment today.

All of this made a growing industry conscious of the need to learn more of the nature and behavior of sounds; speech and music in particular, for these are the intelligible noises which give instruction and pleasure.

It is obvious that the cure for reverberation is sound absorption; however, this cure can be excessive in two ways. Materials may be used which ab THEATRE CATALOG 1948-49
1948-49 Theatre Catalog, 7th Edition, Page 337