EQUIPMENTREPORT IL120s User Manual

As everyone—at least, every-

one who reads this magazine—knows, the
sound of a subwoofer in a room depends
not only on the subwoofer itself, but also on
the room and the placement of the sub­woofer in the room. You can have a sub­woofer that’s a sterling performer when
measured anechoically, but that perfor­mance may not be realized in a given home­theater setting. While some of us are in the
fortunate position of being able to build a
dedicated home-theater room of ideal pro­portions, most of us are stuck with the
rooms we’ve got, which leaves subwoofer
position as a variable to be optimized.

There are formulas and computer pro­grams that will suggest subwoofer position­ing, but, in my opinion, these are not as use-

ful as they seem. The ones I’m familiar with
all use a mathematical model that assumes
a shoebox-shaped room with no openings
in the walls, and walls of infinite rigidity.
Real rooms may be L-shaped and have
doors, archways, closets, skylights, and
cathedral ceilings—variables that can’t be
plugged into the formulas. Real walls typi­cally have rigidity that is considerably less
than infinite, which can affect the useful­ness of the result in ways that are often
unpredictable.

One bit of advice that’s hard to argue with
is that the subwoofer should be moved
around until you find the position that pro­duces the best bass—i.e., the greatest exten­sion, the most output, the flattest frequency
response, and the smoothest integration

with the main speakers. Fair enough, but
even if you ignore the possibility that you’ll
have to make tradeoffs among the different
criteria of subwoofer performance (for
instance, the position that gives you the high­est output might not produce the smoothest
integration), this approach assumes that you
have considerable flexibility in subwoofer
positioning. Again, the reality may be quite
different. The position that’s ideal for the sub­woofer may be exactly where you have the
equipment rack, with no other convenient
place in the room to put the equipment. Or
the subwoofer might sound best when
placed in a position that will almost guaran­tee that people will trip over it or its cables.

Equalization

One approach to improving in-room sub­woofer performance is equalization: atten­uating the peaks and boosting the valleys, a
process intended to produce an overall
more linear frequency response. Unfortu­nately, there are several pitfalls to using
conventional equalization in this fashion.

First, boosting a frequency that corre­sponds to a dip in the frequency response is
not advisable. A dip usually indicates
acoustic cancellation, and boosting the
level at this frequency is like feeding power
into an acoustic black hole. You’ll end up
pushing the subwoofer to high output lev­els, with little to show for it, except possibly
driving the woofer into audible distortion.

Attenuating a peak might be effective,

Interlude IL120s ported active subwoofer
Driver: one 12" C.M.M.D. cone
Frequency response: 28–150Hz, ±3dB
Amplifier output: 500W (20–150Hz,

<0.1% THD)

Crossover frequencies: 50–150Hz,

24dB/octave, continuously variable

Controls: subwoofer level, phase (0°/180°),

crossover frequency, R.A.B.O.S. (see text)

Finishes: cherry, natural maple, onyx-onigre
Dimensions: 17

1

⁄2" × 171⁄4" × 193⁄4"

(H×W×D)

Weight: 45 lbs.
Price: $899; Bass Optimization Test &

Measurement Kit, $59.95

Manufacturer

Infinity Systems
250 Crossways Park Drive
Woodbury, NY 11797
tel. [phone]
fax [phone]
www.infinitysystems.com

SPECIFICATIONS

EQUIPMENT REPORT

Infinity Systems
Interlude IL120s

Robert Deutsch

SUBWOOFER

74 Stereophile Guide to Home Theater • November 2001

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but, as work by Floyd Toole and his associ­ates 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 tra­ditional third-octave Real Time Analyzer
(RTA) measurement can detect, and cor­recting it requires attenuation with a corre­spondingly narrow bandwidth. (I recently
attended a talk given by Toole at a meeting
of the Toronto chapter of the Audio Engi­neering 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 engineer­ing 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. Howev­er, 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 dedicat­ed low-frequency measurement and equal­ization 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 special­ized sound-level meter, test CD, measure­ment 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 res­olution 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 frequen­cy. 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 fre­quencies 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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