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around with the surround preamp-proces-
sor’s subwoofer-level control but couldn’t
get rid of the boomy quality without mak-
ing the subwoofer sound too weak. For the
price, the performance was still good
enough to earn a recommendation, but
nothing to get too excited about.
Once I felt I had a good handle on the
IL120S’s basic sound, it was time to try
R.A.B.O.S. I set up the sound-level meter on
a short tripod placed at the central listening
seat and began adjusting first system vol-
ume, then subwoofer volume, as instructed
by the R.A.B.O.S. manual. That is, I tried
to—before I was able to finish making these
adjustments (which are preliminary to the
fine-grained measurement/equalization
process), the sound-level meter’s Low Bat-
tery warning light came on. The meter had
been on perhaps 15 minutes. Could the
meter’s 9V alkaline battery have been on
the low side to begin with? Perhaps. I
replaced it with a new battery. Another 15
minutes or so of testing, and the Low Bat-
tery light came on again.
Suffice it to say that I exhausted four bat-
teries during the R.A.B.O.S. measurement
process, and would have needed even more
had I not started turning the meter off at
every opportunity. I talked to
Allan Devantier at Infinity
about the meter’s battery-
eating habits, and he admit-
ted that the meter draws
considerable current, but
said that this was a byprod-
uct of making it behave lin-
early at the low frequencies
required for accurate
R.A.B.O.S. measurements. I
think the Infinity people
were gotten to by the Ener-
gizer bunny.
Apart from having to
watch for that pesky Low
Battery warning, the pro-
cess of taking the R.A.B.O.S.
measurements, plotting the
results, and making the
adjustments turned out to
be easier than I had antici-
pated. The plot of the fre-
quency response based on
the R.A.B.O.S. measure-
ments showed that there
was just a single 6dB peak
centered at 40Hz, and the bandwidth selec-
tor (a neat, curve-fitting device) indicated
that the correction should have a 30% band-
width. Then it was a simple matter of look-
ing up in the R.A.B.O.S. manual the control
settings corresponding to these parameters
(e.g., 40Hz is Position 11 of the Frequency
control), and, with the aid of the adjustment
key (a kind of small screwdriver), turning
the equalizer controls to the appropriate
settings.
I then repeated the measurements to
check the effect of the R.A.B.O.S. adjust-
ments. The plot of the retest showed that
the peak centered at 40Hz was essentially
eliminated, with no change elsewhere in
the frequency response. (Actually, there
was still a 1dB blip at 40Hz, but I decided to
leave it alone.) The last stage was setting the
final system balance, using another pair of
test signals on the R.A.B.O.S. test CD.
Comparing the sound of the system with
R.A.B.O.S. engaged vs. bypassed (the sub-
woofer has a switch that allows you to do
this), using R.A.B.O.S. resulted in the IL120S
sounding much more subtle and natural,
more of-a-piece with the rest of the range.
The bass drum in Jumanji—the scene
where the children run upstairs to look for
whatever is making that ominous throb-
bing sound—became tighter, not as boomy,
with less of a sense of prolonged resonance.
The bass also seemed to go deeper. I initial-
ly found the increase in apparent bass
extension puzzling, in that the before/after
frequency-response plot showed no
changes in the region of 30Hz and below.
However, the impression of greater bass
extension does make sense when you con-
sider the fact that R.A.B.O.S. lowered the
40Hz peak while leaving frequencies below
30Hz unaffected. This would have the effect
of the lower frequencies being given more
nearly equal prominence with the higher
ones—which means, effectively, greater
bass extension. The IL120S’s rated low-end
limit is 28Hz, –3dB, and that’s pretty much
how it sounded with the R.A.B.O.S. adjust-
ments. More upmarket subwoofers—like
the Bag End Infrasub-18 and the big Velo-
dynes—go lower and with more authority,
but within its range the IL120S actually had
them beat in linearity of in-room frequency
response. I just wish the powered subs of
my Avantgarde Unos in my 2-channel lis-
tening system were equipped with
R.A.B.O.S. controls.
The improvements brought about by
R.A.B.O.S. were especially welcome with
music. There’s a tendency for the bass in
subwoofer-equipped systems to sound dis-
connected from the rest of the range, which
is more bothersome with music than with
movie sound effects. With R.A.B.O.S., there
was better integration of the sound of the
IL120S with the main speakers, for a more
musically appropriate effect. The bass was
also more “tuneful”—it was easier to follow
string bass and bass guitar lines in the mix.
Conclusion
Considered without the R.A.B.O.S. para-
metric equalizer function, the IL 120s
impressed me as a good subwoofer for the
price, but not one that stands out in any
major way from the competition. But the
R.A.B.O.S. adjustments produced signifi-
cant improvements in measured and sub-
jective performance, the frequency response
becoming much more linear, with audible
improvements in bass evenness, tightness,
and apparent extension.
As far as I’m concerned, the IL120s, with
R.A.B.O.S. optimized, is now the subwoofer
to beat in the under-$1000 category.
INFINITY SYSTEMS INTERLUDE IL120S
78 Stereophile Guide to Home Theater • November 2001
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