Page 25 - Summer 2018

stereophonic sound. To calibrate the positions of the micro- phones in Philadelphia and the setup of the loudspeaker ar- ray in Washington had taken months. Much of the theory of auditory perspective was in place, but the execution required plenty of improvisation and trial and error. Originally, there were meant to be nine speakers on the stage in a three-by- three array, creating a “sheet of sound.” But Fletcher and his engineers realized that only three horizontal speakers would be necessary. In an interview, he recalled, “Well, we were just dumb enough not to realize that on stage people don’t jump up and down... for something like Hamlet’s ghost, it would be alright to have the speakers run up and down. That’s about all there was to that” (Knudsen and King, 1964).
The loudspeakers themselves were a special invention. Based on a study during the rehearsal season by the engineers Wente and Thuras (1934), the loudspeakers were designed to have one enormous drum for transmitting low-frequency sounds with two high-frequency horns sitting atop it. This was inspired by Wente and Thuras’ finding that low-frequen- cy sounds were less spatially directed than high-frequency sounds, and thus a natural compromise in the reproduction system could be reached by allowing the two registers to be transmitted differently.
The transmission system was a technical marvel as well. Al- though the music was ethereal to the audience, the signal bearing the recording of the Philadelphia Orchestra traveled like water through a pipe down the East Coast. Engineer- ing a transmission system that could handle the frequency and amplitude range of the orchestra, without introduc- ing substantial distortion and maintaining a flat frequency response function, was no simple feat. Several challenges stood in the way. First, the ordinary circuits for telephone transmission typically limited signals to 200-3,000 Hz and typically limited the volume range to no more than 30 dB. This was handled by modulating the frequencies of the or- chestral recording up, from 40-15,000 Hz to 25,000-40,000 Hz, and transmitting the high-frequency currents through 3 channels in an all-underground cable with repeaters ev- ery 25 miles (Affel et al., 1934). The signal was demodulated back to its original frequency range in Washington. The fre- quency shift was used to prevent cross talk with other chan- nels on the cable, which were usually transmitted at lower frequencies. Repeaters, equipped with equalizers to pre- vent unintentional attenuation of certain frequencies, kept the signal from losing power as it traveled more than 100 miles. Because the transmission involved higher frequencies than typical phone calls, more repeater stations than usual
were in play that night: stations at the towns of Holly Oak, Delaware, and Elkton, Abingdon, Baltimore, and Laurel, Maryland, bridged the gap between Philadelphia and Wash- ington. For this purpose, two temporary huts to house the repeaters and their power supplies had to be constructed at Abingdon and Laurel.
Amid this demonstration of technological prowess, some- thing fundamental about psychophysics was also shown. Whatever the audience’s psychological experience of the concert—wonder, shock, distaste, or pleasure—they were responding to a stimulus that was as real and plastic to the engineers and Stokowski as clay to a sculptor. The medium of music was no mere incident to its enjoyment but an in- separable and defining part.
The Enduring Legacy of the Collaboration
The collaboration between Bell Telephone Laboratories and Leopold Stokowski lasted until 1940, spanning nearly a de- cade and bringing many demonstrations of stereophonic and enhanced sound to the public, including the one The New York Times deemed the loudest show of all time. Stokowski began splitting off when he was approached by Walt Disney to conduct the epic score of the movie Fantasia. Originally, Disney intended to contract Bell Telephone Laboratories to engineer stereophonic recording for the film to give the illu- sion of instruments following characters across the screen, but the laboratory leadership declined to accept a commer- cial contract. The work instead went to a team at RCA, who leveraged much of the groundwork laid by Fletcher and his associates to build the “Fantasound” system. If you watch Fantasia, the silhouetted conductor who shakes hands with Mickey Mouse is none other than Stokowski (listen to the remastered soundtrack, conducted in its entirety by Sto- kowski, goo.gl/nV44pu; Stokowski talks to Mickey Mouse, goo.gl/bSaofa).
While Stokowski was expanding his cultural influence, Fletcher continued his influential work in psychoacoustics and eventually became a professor at Brigham Young Uni- versity. His lifelong career in research has been renowned for establishing the cornerstone methods of communica- tion science (Allen, 1996), and his contributions to the mu- sic industry were recognized with a posthumous Technical Grammy awarded in 2016 (goo.gl/8B35MG).
That Harvey Fletcher and Stokowski became partners in a joint expedition for nearly 10 years is almost surprising considering their enormously different temperaments: the notoriously impassioned conductor with unkempt hair and
Summer 2018 | Acoustics Today | 23