Acoustic research lst owners manual

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as. Laboratory
Standard

Transducer

Acoustic Research, Inc., 24 Thorndike Street, Cambridge, Massachusetts 02141

Acoustic Research International n.v., Radiumweg 7, Amersfoort, Holland

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AR LABORATORY STANDARD TRANSDUCER

The AR Laboratory Standard Transducer is designed for those laboratory
and commercial applications that require conveniently repeatable, accu-

rately known spectral energy profiles, including one flat profile extending
from 30 Hz to 20 kHz.

The AR-LST uses a 12-inch acoustic suspension woofer, four 1%-inch
mid-range hemispherical radiators, and four 3A-inch hemispherical
tweeters. The individual speakers are identical with those of an Ali-3a
system. Crossover frequencies are 575 and 5,000 Hz.

Four mid-range speakers and four tweeters are included in the AR-LST
to provide increased power-handling ability. Each of these combinations
is wired in series] parallel.

The AR-LST contains an autotransformer with taps at l-db increments
from 0 to - 6 db. Each of the speakers is connected (through its crossover
filter) to one pole of a 3.pole, 6-position selector switch, which is fed by
the autotransformer taps, so that the relative output levels can be adjusted
as desired. A large capacitor in series with the autotransformer prevents
excessive amplifier loading at subaudible frequencies where the trans-
formers inductive reactance decreases.

Switch position No. 1 provides acoustic power response that rises slightly
as frequency increases; the woofer output is 2 db lower than that of the
tweeter. Position No. 2 is the flat energy setting. Positions 3 through 6
provide progressively greater slopes in energy response, with the level of
low-frequency output increasing, relative to high-frequency output, by 2
db for each higher numbered switch setting. In positions 5 and 6 the
balance of the AR-LST is approximately the same as that of an Ali-3a
with its level controls in the suggested normal settings.

Output level of the AR-LST mid-range units is held relatively constant
for all of the six balance switch positions so that the overall impression
of loudness does not change substantially as the switch position is
changed.