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Fig. 4. Notation on back of 22 May 1929 letter.
from 1928 to 1939, were Metro-Goldwyn-Mayer (MGM), Paramount Pictures, Fox, Universal, United Artists, and Warner Brothers.
He suggested that one of the larger theater chains retain an acoustical consultant. He was able to do this as he was already working for MGM in the design of their sound stages. An early letter, from 21 May 1928, discusses the ambient noise level next to the site for a new sound stage (expressed in transmission units, or T. U., that, in 1923, replaced the “standard mile of cable” used by the telephone industry to describe the gain or loss in telephone lines), as well as his rec- ommendations for the construction of the exterior envelope and the treatment of the interior surfaces. He suggests that the envelope of the building be constructed so that it has “an insulation of 60 T. U.” He also says T. U. “is ten times the com- mon logarithm of the energy in the sound compared with the amount of sound energy that is just barely audible.”
One notes in the MGM letters, starting early in 1929,
that Dr. Knudsen uses the abbreviation dB per the adoption
of the decibel as the base 10 replacement for the transmission
13
unit. The neper was adopted as the replacement for the base
e unit.
Another letter to MGM, dated 1 March 1929, discusses
the acoustics of motion picture theaters. In this letter Knudsen talks about sound isolation, reverberation, and heating, ventilating and air conditioning (HVAC) noise. One would think that these design issues would have long since been defeated, but recent experiences in some cinemas prove otherwise.
The Academy of Motion Picture Arts and Sciences (AMPAS) contacted Knudsen, after the first meeting of the Society in 1929, asking that he keep them abreast of advances of interest to them. He had a long relationship with
the Academy—working with the technical side as well as with the constituent members—the studios. Dr. Knudsen was consulted by the Society of Motion Picture Engineers (SMPE; the Television came later) about set-up and tuning of the loudspeaker playback system, the B-chain, in theaters. In 1939 a committee, consisting of Vern O. Knudsen, Paul A. Sabine, George T. Stanton, Hugh S. Knowles, Keron C. Morrical, and John S. Parkinson, was appointed at the Society’s Iowa meeting to work with the AMPAS Research Council on establishing acoustical measurements in the- aters. As with the acoustics of cinemas, this area is still being investigated, currently by the SMPTE ST-SG Theatre B- Chain study group.
Vern Knudsen worked with many cinema pioneers, among them Lester Cowan14 of AMPAS and Douglas Shearer.15 The late 1920’s and 1930’s were heady times for the industry and Knudsen was in the thick of it with acoustic analyses of motion picture set materials, reverberation time recommendations for studios and theaters, measurement methods and equipment (with Ludwig Sepmeyer and the Delsasso brothers), reports on sound playback, sound isola- tion, and human hearing.
Knudsen’s evaluation and application of various materi- als for use as finishes and in the construction of buildings was a practical application of acoustics for production and exhi- bition spaces. It was still in its beginning phase in the late 1920’s and early 1930’s. Many of the materials and methods now in use had their first acoustic investigation with Dr. Knudsen’s research, as detailed in his correspondence with Harvey Fletcher, William P. Snow, Wallace Waterfall, Paul E. Sabine, Floyd R. Watson, Warren P. Mason, and Floyd Firestone (who is credited with coining the phrase “Lamb Waves”), among others.
32 Acoustics Today, January 2011