The project to design the Shearer Horn had its roots in 1933. In that year, John Hilliard contacted Western Electric (WE), on behalf of his employer MGM, to develop a prototype for a new loudspeaker. The intent was to address deficiencies in the WE "Wide Range" speaker system that was the standard of the day. The "Wide Range" system consisted of two WE 555 compression driver attached to 12' "snail horns" with four 18" bass drivers mounted on an open baffle. Two separate "Bostwick Tweeter" covered the high end to result in a three-way system.
The deficiencies of this system were many. The efficiency and low end response were restricted by the open baffle bass drivers and the distortion of these drivers was high. The most significant deficiency, in John Hilliard's mind, was the phase discrepancies between the WE555's and the other drivers. The 12' horn paths so delayed the midrange response that monitoring tests of a tap dance routine resulted in two taps being heard for every one recorded.
Hilliard was aware of research work being undertaken by Bell Labs that resulted in the Fletcher System. That system was used in a prototype, stereophonic demonstration. Hilliard's inclination was to have WE develop a marketable loudspeaker system based on that prototype. In 1934, a full year after Hilliard contacted WE with this proposal, he was dismayed to discover that they had not made any progress.
Around this time, Jim Lansing and his designer, Dr. Blackburn attended the Society of Motion Picture Engineers (SMPE) show at Knickerbocker Hotel in Hollywood. Western Electric was demonstrating their "Wide Range" system and Jim and Dr. Blackburn decided to take a close look at it. They noted some obvious deficiencies and Jim began to develop ideas on how to improve that system. Shortly after returning to Los Angeles, Dr. Blackburn met with his close friend John Hilliard. At one point the discussion turned to the poor state of movie sound systems. He relayed their experiences at the SMPE show and Lansing's thoughts on how loudspeakers could be improved. The meeting concluded with the idea that John Hilliard, MGM and Lansing Manufacturing should get together and discuss this further.
This was the genesis of the Shearer Project. John Hilliard approached the head of MGM's sound department, Douglas Shearer, with a proposal to develop their own system. There was no love lost between MGM and WE since the latter was perceived to be an unresponsive monopoly. Douglas Shearer didn't hesitate to approve the Hilliard's proposal and authorized "any reasonable budget". Hilliard became the team leader of this new project. Hilliard immediately recruited Lansing Manufacturing, Robert Stephens, a design draftsman on MGM's staff, and Harry Kimball.
Hilliard set the original design parameters for the project and described a concept of a two-way design. He proposed using a compression driver and multicellular horn, similar to that employed in the Fletcher system, and 15" cone speakers mounted in either baffles or horns. Design of the drivers was the responsibility of Lansing Manufacturing. Robert Stephens undertook the design of the geometry of the multicellular horns and their manufacture in MGM's shops. Harry Kimball was responsible for the crossover. In addition to his duties in overseeing the project, Hilliard worked on the preliminary designs for flat baffles and horn alternatives for the bass drivers.
The first result of Lansing Manufacturing's work was the 15XS field coil bass driver. It was a rugged, efficient, high precision unit using a seamless paper cone attached to a 2" round wire voice coil. The original high-frequency driver that they developed for this project was the 284, which was also a field coil unit using a 2.84" flat wire voice coil attached to a 2.84" aluminum diaphragm. An annular slit phase plug was employed in back of a horn throat that had a 1.5" exit diameter. After initial development, a concern was raised that the use of an annular slit phase plug may be in violation of Bell Lab's patent on the WE594 driver. Dr. Blackburn undertook a redesign of this phase plug to a radial slit configuration. Thus was born the 285 driver that was ultimately used in the production systems.
Hilliard continued with work on the bass module configuration. By this time he was leaning towards the horn alternative, but envisaged a direct horn path. Both RCA and WE became aware of the Shearer Project and were now interested in participating. RCA's Harry Olsen suggested using one of their folded horns. This had the advantage of significantly reduced size, particularly in depth for use behind a projection screen. Hilliard was quick to adopt this design as the basis for the Shearer Horn. By 1935, a prototype was in place using a re-entrant low frequency horn powered by four Lansing 15XS drivers. On top of this was mounted a multicellular horn designed and built by Stephens. It should be noted that Stephens developed a number of multicellular horn patterns depending on the requirements for individual theaters. Hilliard felt it was imperative to avoid the problems of multiple horn overlap. Therefore, horns with cell patterns of 2x4, 2x5, 2x6, 3x3, 3x4 and 3x5 ( all using a 17° x 17° dispersion cell) were developed for use in differently dimensioned theaters. A single Lansing 284 compression driver was initially employed on these horns.
The new Shearer system was now ready for testing and it proved an unqualified success. The bass horn configuration contributed to an overall system efficiency near 50%. The bass horn sensitivity so closely matched that of the high frequency unit that no more than 2 db of attenuation was required. It achieved a flat frequency response of +/- 2db for a bandwidth of 50-8,000hz. The position of the 284 driver, in relation to the position of the bass drivers, had been carefully designed to result in a phase delay of no more than 1 millisecond.
MGM built 12 Shearer Horns for subsequent theater tests in a number of different cities. It confirmed the positive results from the development testing and production was ordered for 150 units for use in MGM's Loews's Theater Circuit. WE and RCA each received contracts to build 75 units. RCA sub-contracted with Lansing Manufacturing for the then used 285 compression driver and 15XS bass driver.
It is interesting to note that Lansing Manufacturing was not a recipient of one of the original contracts to MGM. The reasons for this are not clear given their involvement in the original design. Nonetheless, it appears that MGM did not, or possibly could not, enforce intellectual property rights to the Shearer design. Lansing was soon in business selling their own system to the entire movie industry and gained a reputation as producing the finest example of the type. More prestige theaters and studio screening rooms used Lansing systems than any of the competing designs.
Curiously, Lansing was the only manufacturer to advertise their system as the Shearer Horn. WE used the trade name Diaphonic and RCA marketed several versions of Shearer type systems under their Photophone trade name. The reasons for this are unknown. It may be that Lansing Manufacturing received exclusive rights to the name as a result of their involvement in development. Conversely, it could be that WE and RCA saw no advantage to using a trade name associated with someone outside of their firms. Nonetheless, the Shearer association proved of great value to Lansing Manufacturing. They would develop a number of very successful theatre systems based on Shearer concept as illustrated below.
The impact of the Shearer Horn on the movie industry is hard to overstate. Virtually every movie loudspeaker manufacturer adopted the Shearer Horn as their standard. It was considered such a significant advance that it received a technical achievement award at the 1936 Academy of Motion Picture Arts and Sciences ceremony. Lansing Manufacturing became a major presence in the movie sound industry almost overnight. The Shearer Project was also to give rise to one of Lansing's biggest competitors – Stephens Tru-Sonic. Robert Stephens left MGM shortly after the completion of the Shearer project to found this firm. For the next few years, until the formation of Altec Lansing, these two firms were committed, but friendly rivals.
© 2000 Don McRitchie