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but, as work by Floyd Toole and his associ-
ates at the National Research Council in
Ottawa has shown, the bandwidth of the
sort of peak you’re likely to encounter with
subwoofers is often narrower than the tra-
ditional third-octave Real Time Analyzer
(RTA) measurement can detect, and cor-
recting it requires attenuation with a corre-
spondingly narrow bandwidth. (I recently
attended a talk given by Toole at a meeting
of the Toronto chapter of the Audio Engi-
neering Society, where he exhorted the
assembled AES members—most of whom
work in pro audio—to throw away their
third-octave RTAs.)
R.A.B.O.S.
Floyd Toole—now vice president of engineer-
ing at Harman International Industries, Inc.,
of which Infinity Systems is a division—
acknowledges that optimizing subwoofer
performance starts with positioning the sub-
woofer in the room, and that this typically
involves some practical constraints. Howev-
er, while rejecting the use of conventional
RTA-based equalization, he suggests that a
subwoofer’s performance can be improved
considerably using what he and Allan
Devantier, Harman’s director of engineering
and another National Research Council
alumnus, call R.A.B.O.S.: Room Adaptive
Bass Optimization System. This is a dedicat-
ed low-frequency measurement and equal-
ization system incorporated into Infinity’s
current line of subwoofers and full-range
speakers that include a subwoofer (including
the Prelude MTS, reviewed by Joel Brinkley in
the July/August 2000 issue of the Guide).
R.A.B.O.S. is supplied as an optional Test
& Measurement Kit that contains a special-
ized sound-level meter, test CD, measure-
ment templates, bandwidth selector, and
an adjustment “key.” (An adjustment key is
included with the IL120S even if you don’t
get the Test & Measurement Kit. In that
case, you can try adjusting the controls by
ear, listening to music of appropriate bass
content.) The frequency bands on the test
CD that form the basis of the measurement
cover the bass range with much greater res-
olution than a third-octave RTA: there are
23 test frequencies from 20Hz to 100Hz .
R.A.B.O.S. employs a type of parametric
equalizer, and differs in several important
respects from conventional RTA-based
approaches. The parameters that can be
adjusted are level, bandwidth, and frequen-
cy. The controls for level (attenuation only,
from 0dB to –14dB) and bandwidth (from
5% to 50% of an octave) each have 21 steps.
The frequency control has 19 steps from
20Hz to 80Hz, each corresponding to fre-
quencies on the test CD.
The setup procedure requires that you
first plot the subwoofer’s response using the
test frequencies and the sound-level meter,
INFINITY SYSTEMS INTERLUDE IL120S
PHOTOS © 2001 CORDERO STUDIOS
Stereophile Guide to Home Theater • November 2001 75
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