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which determines the frequency of the
dominant subwoofer/room peak as well as
the shape of that peak. You then set the
bandwidth control to match the shape of
the peak, and attenuate level at the appro-
priate frequency by an amount that will pro-
duce a flat frequency response. After the
equalization process is completed, you can
check the results by repeating the test tones
and plotting the frequency response again.
R.A.B.O.S. can correct for only a single dom-
inant peak, but this is said to be the most
common subwoofer/room interaction. In
situations where there are two significant
peaks, the R.A.B.O.S. manual suggests cor-
recting the one at the higher frequency,
which is likely to be more audible and
objectionable. If there are adjacent narrow
peaks and dips, the manual says to leave
them alone—they’re the result of interfer-
ence patterns that are specific to a certain
spot in the room, and in any case can’t be
corrected by this type of equalization.
Oh yes, the subwoofer . . .
Aside from the R.A.B.O.S. function, the
IL120S looks like a fairly conventional pow-
ered subwoofer with a rear-facing port that’s
flared to reduce turbulence. The IL120S is
not one of those newfangled ultra-compact
subs, and does not have servo control. How-
ever, it does have one high-tech feature: the
driver is a special 12-inch unit with a propri-
etary Ceramic Metal Matrix Diaphragm
(C.M.M.D.) and a 60-oz magnet structure.
According to research reported in a white
paper on www.infinitysystems.com, loud-
speaker cones made of C.M.M.D. have
fewer inherent resonances and are capable
of more linear pistonic movement than any
other comparable material. The effect is
said to be the elimination of colorations due
to cone modes, which should result in dra-
matically reduced distortion.
Amplification is provided by a 500W
class-AB amplifier with a cool-running
switching power supply. In addition to the
R.A.B.O.S. controls, the IL120S includes a
phase-reversal switch and a continuously
variable lowpass filter that can be turned
off if the subwoofer is used with a Dolby
Digital/DTS surround processor-receiver.
The IL120S’s sculpted front panel and grille
are attractive, and the review sample was
finished in “onyx-anigre,” which I take to be
a term for a better class of fake wood.
Listening
Before trying to fine-tune the IL120S with
R.A.B.O.S., I wanted to check out its raw
performance with the R.A.B.O.S. controls
turned off completely. I set up the IL120S as
per my usual practice: sub placed at front
left, just a bit out from the corner, the main
speaker/subwoofer balance adjusted using
the built-in calibration tones of the Rotel
RSP-976 surround preamplifier-proces-
sor—or, when using the Thule PR 250B
processor (which lacks a subwoofer calibra-
tion tone), the test tones on Stereophile’s
Test CD 3. To ensure comparability with my
previous subwoofer reviews, I used a
RadioShack sound-level meter.
Over a period of several weeks, watching
familiar DVDs as well as new releases (I rent
many more than I buy), the impression that
I formed of the IL120S was that, for $899, it’s
a competent but unexceptional performer.
Extension was good, and there was lots of
volume available, but the bass was a bit
boomy, lacking some tightness. I played
INFINITY SYSTEMS INTERLUDE IL120S
Sources
Rotel RDV-1080 DVD player
JVC HR-4700U VCR
Surround Preamp-Processors
Rotel RSP-976
Thule PR 250B
Power Amp
Bryston 9B-ST
Speakers
Dunlavy SC-I (5)
Cables
Digital: TARA Labs Decade
Interconnect: assorted AudioQuest
Speaker: AudioQuest Type 6+
Misc.
Chang Lightspeed CLS HT1000 power-line
conditioner
AudioPrism QuietLine LF-1 Mk.II parallel
power-line filters
REVIEW SYSTEM
76 Stereophile Guide to Home Theater • November 2001
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