The public-address age

In 1915 Edwin Pridham and Peter Jensen put the pieces together in San Francisco. Their Magnavox TelemegafoneMagnavoxMagnavox Telemegafone1915 public demonstrationAn early complete sound-amplifying system built around a moving-coil horn driver.Open profile → paired a carbon microphone with a moving-coil driver and horn, and the later Type R2MagnavoxTelemegafone Type R21920The Magnavox Telemegafone Type R2 was a moving-coil horn loudspeaker with a field-coil driver and a swan-necked metal horn, sold to pair with a separate radio. Variants included the R2A, R2B and R2C.Open profile → carried the idea into production. A Magnavox installation supported President Wilson’s 1919 address in San Diego. At the Christmas Eve demonstration about 100,000 people heard music and speeches beside Mayor James Rolph. Six days later Governor Hiram Johnson, too ill to attend, addressed the Civic Auditorium through the system from his home. Histories argue over which event was the ‘first PA’; what matters is that a complete, scalable chain now existed.

Magnavox Magnavox TelemegafoneEdwin S. Pridham & Peter L. Jensen · Public domain (US patent)Magnavox Telemegafone Type R2Edwin S. Pridham & Peter L. Jensen · Public domain (US patent)

Western Electric turned that chain into an engineered system. The 1-A public-address system was built around valve amplifiers. The 555 compression driverWestern ElectricWestern Electric 5551926A highly efficient compression driver used with large theater horns.Open profile →, designed by E. C. Wente and A. L. Thuras, fed horns such as the 12-AWestern Electric12-A horn1926–1927The Western Electric 12-A was a large wooden exponential horn with a 45-inch-square mouth and an 11-foot folded path, driven by the [[western-electric-555|555-W]] compression driver during the conversion to talking pictures.Open profile → and 15-A. The 594-AWestern Electric594-A driver1930sThe Western Electric 594-A was a theatre compression driver with a multi-slit phasing plug. JBL historical research compares its phasing-plug geometry directly with that of the later [[jbl-375|JBL 375]].Open profile → driver pushed bandwidth higher still. Cinema sound grew from the same parts in the Mirrophonic system and RCA’s PhotophoneRCAPhotophone theatre system1928RCA Photophone was RCA's variable-area optical sound-on-film system, marketed from 1928 against Western Electric. RCA also supplied complete theatre equipment: amplifiers, sound heads and horn loudspeakers.Open profile →. Those theatre systems then became the testbed for live reinforcement.

Western Electric Western Electric 555Edward C. Wente (Bell Telephone Laboratories) · Public domain (US patent)Western Electric 12-A horn© FOH magazine; photographer not credited · Rights retained by the rights holder; reproduced for historical commentaryWestern Electric 594-A driverEdward C. Wente (Bell Telephone Laboratories) · Public domain (US patent)RCA Photophone theatre systemRCA Photophone, Inc. (The Film Daily, 1929) · Public domain

The 1930s split the spectrum between dedicated devices. The Shearer hornMGM / LansingShearer Horn system1935–36The Shearer Horn was developed from 1933–34 by John Hilliard of MGM's sound department, under Douglas Shearer, with James B. Lansing, to fix the time smear of Western Electric's Wide Range system. It combined 15-inch drivers in a bass horn with a multicellular horn and compression driver, and won a Technical Achievement Academy Award in 1936.Open profile → put compression drivers on multicellular horns over a folded bass horn; Lansing’s 1937 IconicLansing ManufacturingIconic loudspeaker1937The Lansing Iconic of 1937 paired a 15-inch bass-reflex woofer with a horn-loaded compression driver. It grew from Lansing's [[shearer-horn|Shearer Horn]] work via the smaller Monitor System 500.Open profile → shrank the idea into a 15-inch bass-reflex woofer topped by a horn-loaded driver. Permanent-magnet driversJensenPermanent-magnet dynamic driver1930In 1930 Jensen introduced what it describes as the first permanent-magnet dynamic loudspeaker, replacing the electromagnet field coil of earlier dynamic speakers with a built-in permanent magnet. This removed the need for a separate field supply, simplifying installation in radios and sound equipment.Open profile → freed loudspeakers from field-coil power supplies. At the other end of the chain, the Marconi–ReiszMarconiMarconi-Reisz microphone1925–1927The Marconi-Reisz microphone held carbon granules between electrodes in a hollowed marble block behind a thin diaphragm. It was the BBC's standard studio microphone from 1926 to 1933, replacing noisier Peel-Conner carbon microphones, and needed turning daily to keep its granules from settling.Open profile → carbon microphone gave way to the RCA 44-BXRCA44-BX ribbon microphone1931 (44-A); 1940 (44-BX)Harry F. Olson's ribbon research at RCA led to the Type 44-A velocity microphone in 1931. In 1940 RCA updated it with improved magnet material as the 44-B and 44-BX, and marketed it as the standard microphone of broadcasting; the 44 and related 77 series stayed in production until 1957.Open profile → ribbon, the 618AWestern Electric618A dynamic microphone1931The Western Electric 618A, developed by Bell Labs engineers E. C. Wente and A. L. Thuras, was among the first commercially produced dynamic microphones. A duralumin diaphragm drove an aluminium-ribbon coil in a cobalt-steel magnet field, giving a quoted range of 35 to 9,500 cycles per second with no polarising voltage.Open profile → moving-coil microphone and Shure’s Model 55 UnidyneShureModel 55 Unidyne1939The Shure Model 55 Unidyne of 1939 was the first microphone to obtain a cardioid pattern from a single dynamic cartridge rather than by combining two elements. It used engineer Benjamin Bauer's Uniphase principle, covered by US patent 2,184,247, granted December 1939.Open profile →, whose cardioid pattern rejected the loudspeakers behind it. Each improvement on one side made more gain usable on the other.

MGM / Lansing Shearer Horn system© Harman International; courtesy Mark Gander and John Eargle · © Harman International / Lansing Heritage archive; used for identification and historical commentaryLansing Manufacturing Iconic loudspeaker© FOH magazine; photographer not credited · Rights retained by the rights holder; reproduced for historical commentaryJensen Permanent-magnet dynamic driverJensen Radio Manufacturing Co. (1945 advertisement) · Public domainMarconi Marconi-Reisz microphoneJan Kameníček · CC BY-SA 4.0RCA 44-BX ribbon microphoneRoadside Guitars · CC BY-SA 2.0Western Electric 618A dynamic microphoneAlbert L. Thuras (Bell Telephone Laboratories) · Public domain (US patent)Shure Model 55 UnidyneHolger.Ellgaard · CC BY-SA 3.0

Distributed constant-voltage lines allowed one amplifier to feed many loudspeakers over long cable runs. Stadium and civic installations such as the Madison Square Garden system and the 1939 World’s Fair PARCA / Western Electric1939 World’s Fair PA1939RCA's commercial sound catalogue describes its PA and broadcast control equipment as the nerve centre of a fair-wide network of RCA sound apparatus at the 1939 New York World's Fair, including recorded music and narration inside the Perisphere's 'Democracity' exhibit.Open profile → put coverage and intelligibility ahead of fidelity.

RCA / Western Electric 1939 World’s Fair PAUnknown · Public domain

Marconi, which had formed a public-address department in the early 1920s, carried King George V’s opening speech at the British Empire Exhibition at Wembley in 1925 to about 90,000 people through six long-range loudspeakers. In 1929 a Marconi system for the Schneider Trophy race used 200 horns.