Vivid Audio V1w - Manual (Page 11)

1930 - Albert L. Thuras filed patent No. 1,869,178 on Aug.
15, 1930, granted July 26, 1932, for the bass-reflex
principle while working at Bell Labs. Early cabinets used a
passive baffle to direct sound to the front, allowing the
back of the cabinet to be open for the low sounds. The
bass-reflex enclosure kept the low-frequency sounds from
being lost from the rear of the diaphragm.
1931 - Bell Labs developed the two-way loudspeaker,
called "divided range" for the demonstration by H. A.
Frederick in December of vertically cut records. The high
frequencies were reproduced by a small horn with a
frequency response of 3000-13,000 hz, and the low
frequencies by a 12-inch dynamic cone direct-radiator unit with a frequency response
within 5db from 50-10,000 hz. By 1933, a triple-range speaker had been developed
for the Constitution Hall demo in April, adding Western Electric No. 555 driver units
as the mid-range speaker. For the low frequency range 40-300 hz, a large moving
coil-driven cone diaphragm in a large baffle expanding from a 12-in throat to a 60-
inch mouth over a total length of 10 ft. This 3-way system was introduced in motion
picture theatres as "Wide Range" reproduction.
Thuras bass-reflex patent
1932 - RCA demonstrated a dual-range speaker of its own design for theatres, using
three 6-inch cone diaphragms with aluminium voice coils in divergent directions, with
a response of 125-8000 hz, and 10-ft. horns 40-125 hz.
1933 - "Progress was such that a demonstration of the new system - called
"stereophonic" because of its ability to give a spatial sense corresponding to
stereoscopic vision - was given before the National Academy of Sciences and many
invited guests at Constitution Hall, Washington in the spring of 1933. Transmission
was
over wire lines from the Academy of Music in Philadelphia and
three channels were used with microphones respectively at left,
centre and right of the orchestra stage and loud speakers in
similar positions in Constitution Hall." This transmission of music
"was carried out with special loud speakers developed for the
purpose by Dr. Wente and the late A. L. Thuras. The objectives
in the design of these loudspeakers were uniform response over
the whole tonal range of the orchestra, an enhanced sound
power output capacity without noticeable non-linear distortion
and uniform distribution of the emitted sound at all frequencies
throughout a wide solid angle. For the receiving unit and the
multicellular horn which were developed for this demonstration,
Dr. Wente, jointly with the Bell Telephone Laboratories, was
awarded a gold plaque by the Academy of Motion Picture Arts and Sciences in
1936." (Bell Labs, 1953)
Thuras theater
speaker 1933, from
AT&T Archives
1935 - Douglas Shearer and John Hilliard at MGM developed a standard theatre
speaker system, starting with the Loews 5000-seat Capitol Theatre on Broadway.
James Lansing and Dr. John F. Blackburn of Cal Tech designed a 2-way speaker
system; the high frequency driver had a 3-inch aluminium diaphragm and throat size
of 1.4 inches; the low frequency baffled cone unit was 15 inches. ERPI provided
speakers from Fletcher's hi-fi experimental equipment to help design the speakers.
The low frequency horn used four 15-in. Lansing cone drivers and Lansing 284
drivers for multicell horns of different sizes. The system was installed in 12 theatres
for the opening of "Romeo and Juliet" with Norma Shearer, sister of Douglas,
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