Horns, Part 2

In our last issue we looked at the historical and physical forebears of horn loudspeakers. Horns---either actual animal horns or manmade constructions that mimicked animal horns---are found being used to amplify sound as far back as there is recorded history. It’s hardly surprising, then, that horns quickly became part of the picture in sound reproduction, just as they had been in sound production. Horns became an integral part of early phonographs to increase the volume of sound produced by mechanical sound-boxes, both the familiar external straight-sided trumpet and flared morning glory varieties, and more complex geometries contained with the cabinetry of console phonographs. When Peter Jensen and Edwin Pridham developed the moving coil loudspeaker in 1911 (as described in Vintage Whine #9), the first thing they did was couple it to a horn, to make it louder. In this initial case, it was too loud, and we had the first recorded instance of acoustic feedback. The horn was coupled to the throat of the speaker, labeled #2 in the bottom diagram. Jensen and Pridham permanently coupled their prototype to a horn, and mounted it atop the chimney of their building. The two played records through the set-up, which locals were said to enjoy, miles away. With the onset of electrical amplification, large public address systems became possible; in 1915, such a Jensen-Pridham "Magnavox" system provided Christmas music to a crowd of 100,000 in San Francisco. In 1919, Woodrow Wilson became the first American President to be electrically amplified through a Magnavox system, delivering a speech to a sizable crowd. Starting in the teens and going into the 1920's, the Bell System's Western Electric division, known primarily as a manufacturer of telephone receivers, became one of the first manufacturers of "Loud Speakers" for home radio sets. Prior to this, individual listeners had to utilize earphones; the new "receivers" (telephone parlance was still used to describe the speaker units) allowed a roomful of folks to listen at the same time. Note that the $161 set-up shown below was fully half the price of a contemporary Ford Model T, and would be equivalent to about $2200 today. As the years went on, Western Electric became a leading provider of broadcast and sound-reinforcement systems, and became involved with movie theater sound in its earliest days. A wide variety of horn systems was designed and produced to suit theaters of all shapes and sizes; the fascinating Movie Mice website shows a number of such systems. The amazing dual-horn 16A system is shown below, with four 555 compression drivers. The leading WE theater system was known as the "widerange" system, for its broad frequency response (keep in mind that meant it still dropped like a rock above 10 kHz). As detailed in a fascinating piece on the excellent Lansing Heritage website, that system had serious problems, mostly due to the phase delays between the WE 555 compression drivers mounted on long "snail-horns" and the bass drivers, as well as high distortion and low efficiency from the open-baffle 18" woofers. The next level of development in theater sound systems initiated due to dissatisfaction with the Western Electric "Widerange" system---and this is where the genealogy becomes confused---and confusing. Again, thanks to Lansing Heritage for keeping the story straight. John Hilliard of movie studio MGM's sound department sought to create a system that overcame the problems of the WE "Widerange" system, and approached WE about doing so. After a year, nothing had happened, and Hilliard was approached by Jim Lansing and Dr. John Blackburn of Lansing Manufacturer (antecedent of both Altec-Lansing and JBL), who had similar concenrs about theater sound systems. Given the go-ahead from Douglas Shearer, head of MGM's sound department (and brother of actress Norma Shearer), the group began work on what was ultimately known as the Shearer Horn (shown at the top of the page). The system was two-way, with a bass re-entrant horn (as opposed to the "Widerange" system's open baffle) using four 15" Lansing field-coil woofers, crossed over at 500 Hz to a multicellular horn designed and built in MGM's shops by Robert Stephens (who later founded speaker manufacturer Stephens Tru-Sonic). A wide variety of cell configurations were developed to suit theaters of varied sizes and shapes; all used Lansing-built compression drivers. The system was found to be far superior to the WE system that provoked the project; superior enough, in fact, that Western Electric developed its own version using their own drivers, and marketed it as the "Diaphonic" system. RCA marketed several similar systems, and Lansing Manufacturing had exclusive rights to the name "Shearer Horn". Douglas Shearer himself won a Best Technical Achievement Academy Award ("Oscar") in 1936 for his role in development of the horn that bore his name. The Shearer Horn not only set a standard for horn speakers that continues to influence design to this day, but the alliances it created changed the structure of speaker manufacturers in America. We'll look into that more in Part 3, in the next issue of Copper.