Vivid Audio GIYA Owner's Manual page 21

THURAS BASS-REFLEx PATENT
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 s as "Wide range" reproduction.
1932 - rCA demonstrated a dual-range speaker of its own design for s, 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
ChAPter 6 19