Acoustic research lst owners manual

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acoustic research lst owners manual

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Page 1

as. -˜ Laboratory


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

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

Page 2


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

rately known spectral energy proļ¬les, including one flat proļ¬le 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
ļ¬lter) 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 ampliļ¬er loading at subaudible frequencies where the trans-
former-™s 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 -œnormal- 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