Infinity Modulus loudspeaker & Modulus subwoofer

As much as I'm tempted by the impressive sweep and scale with which some of the large, full-range loudspeakers endow music, for some reason I find myself more at home with more compact examples of the breed. This is not through lack of familiarity with large speakers, a pair of B&W Matrix 801s occupying pride of place in our living room (which also serves as my wife's listening room). Yet I find myself hankering after that ultimate soundstage precision that only minimonitors seem capable of producing: the loudspeakers totally disappearing, vocal and instrumental images hanging in space, truly solid—the prefix "stereo-" is derived from the Greek word stereos, which means solid—so that a rectangular, totally transparent window into the concert hall opens at the rear of your room. In addition, the necessarily limited low-frequency extension offered by small speakers makes it much easier to get the optimum integration with the room acoustics below 100Hz.

If only the loudspeakers that were the champs at that didn't at best reproduce instrumental sounds in such Munchkinesque a fashion or, at worst, present them with all the weight and life sucked out of them. Hence my quest to find a small, high-performance loudspeaker which nevertheless presents musical sound in a sufficiently natural manner that you are not continually reminded of the speaker's lack of ultimate bass extension. I eagerly await delivery of a pair of Wilson WATT IIs; in the last five years or so, the only small speakers that have gone some way toward meeting my criteria are the Celestion SL600Si and SL700, the Rogers LS3/5a, and the Acoustic Energy AE1, with the Spica TC-50 an honorable runner-up (footnote 1). All are excellent but very different examples of the genus minimonitorus, with very different balances between strengths and weaknesses. But if I had to choose just one small speaker to listen to for the next 10 years, any one of those would suffice.

But I'm still on the lookout for that ultimate minimonitor, the speaker that apart from having a lightweight low register would give away nothing to the very best full-range speakers. Which brings us neatly to the subjects of this review. Infinity's Modulus is an example of the direction taken by designers of high-performance minimonitors: extensive use of high technology to max out on a small speaker's intrinsic merit.

Infinity Modulus
Although it was first shown at the 1989 Chicago CES, the tiny Modulus didn't go into full production until earlier this year. Although it can be used in its own right, it is recommended for use as the basis for a full-range system when allied to Infinity's Modulus Subwoofer. Matching floor stands and wall-supports are available; the entire system has obviously been extremely well thought-out in terms of integration and ease of setup.

The Modulus Satellite looks immaculate, being finished on all surfaces except the front in glossy black or white polyester resin. The sealed cabinet is constructed from, to quote from Infinity's literature, "extremely stiff, ultra-high-density multi-fiber panels laminated to an acoustically absorptive, visco-elastic substrate." After reading that, you can probably understand that the very first thing I did was to subject the cabinet to the knuckle-rap test. Well, the Modulus cabinet is dead. All I got for my pains were sore knuckles. As well as the damping pads attached to the cabinet's interior walls, a horizontal brace locks the front, back, and sidewalls together just above the woofer, and the interior is filled with acoustic wadding.

The sculpted-looking front baffle is molded in structural foam and sports two drivers on its stepped profile. The woofer features a tiny (3.25" diameter) curvilinear cone, injection-molded from polypropylene loaded with graphite fibers to give a high stiffness/mass ratio, and is constructed on a diecast aluminum basket. The half-roll surround is butyl rubber to damp standing waves within the cone, and the unit is intended to handle frequencies up to 4kHz. The tweeter is the EMIT-k as used in the IRS Beta and IRS V loudspeaker systems. This is a ribbon unit where a voice-coil is etched on a Kapton substrate and freely suspended between the poles of powerful neodymium magnets.

Unlike the more expensive IRS loudspeakers which use, I believe, first-order crossovers, the Modulus marries the outputs of its two drivers with a fourth-order type. This is constructed on a small printed circuit board attached to the rear of the two pairs of binding posts. Component quality is high, the capacitors (apart from one electrolytic) being SiderealKaps and the inductors ferrite-cored. The cables from the crossover to the drive-units are terminated with push-on tags, however, rather than with solder joints. The binding posts are supplied with the two positive and two negative posts strapped with sturdy, gold-plated bars. These can easily be removed to allow bi-wiring or bi-amping. Above the terminal posts is a coin-slot–operated tweeter-level control.

Both drive-units are fixed in place with four Allen-head bolts. It's always a good idea to check the tightness of drive-unit mounting bolts, as I've known them to work loose in shipping. Everything was secure with the Infinity Modulus, however; a good sign.

It might be thought that the part of the stepped baffle immediately beneath the tweeter might interfere with its sound. The ribbon, however, being significantly longer than it is wide, will have limited vertical dispersion in the frequency region it is asked to handle, and won't "see" the obstruction. This won't necessarily be true for the grille and its frame, however, and Infinity's engineers have to gone to considerable trouble to render this acoustically transparent. Black material is stretched over a minimal space-frame molded from what appears to be polystyrene. When in position, the grille completes the rectangular appearance of the loudspeaker.

The Modulus subwoofer is an almost cubical unit finished in the same high-gloss finish as the satellites and resting on four "Iso-tip" conical feet. A single 12" drive-unit, fitted with an IMG cone and driven by an integral 250W amplifier, adorns one face, this normally being covered by a black cloth grille. One of the unit's vertical corners consists of the vertically ribbed heatsink fins for the power amplifier; these got hot only under sustained drive with music having a large amount of sub-100Hz information—okay, organ music!

As with Infinity's IRS subwoofers, the Modulus drive-unit is servo-controlled, both to minimize distortion and to flatten and extend the system's response below its natural resonance. The woofer's drive signal is supplied to the unit via a long cable fitted with 5-pin DIN plugs on both ends. One plug fits into the base of the subwoofer next to its on/off switch, the other into the control unit, which can be sited near the system preamplifier. The control unit takes the stereo outputs from the preamp, passively high-pass–filters them with an array of 0.22µF series capacitors—the exact number of capacitors in circuit depends on the power amplifier's input impedance—and sends the equalized signals to the power amplifiers used to drive the satellites.

It also combines the channels, low-pass–filters the resultant mono signal, and sends that signal to the subwoofer. The high-pass capacitor configuration is adjusted by means of two DIP-switch arrays on the rear panel; the low-pass crossover frequency, subwoofer level, and phase (continuously variable from 0° to 180°) are adjusted with front-panel rotary knobs. A switch allows the user to choose between extension to 22Hz (–3dB) or 35Hz, the latter being useful in problem rooms or with sources having excessive rumble. When the subwoofer is on but the control unit off, the unit goes into standby mode, this indicated by a red LED under the grille lighting.

Footnote 1: Which I reviewed in Vol.12 No.5, Vol.11 No.9, Vol.12 Nos.2 & 3, Vol.11 No.9, and Vol.12 No.10, respectively.
Infinity Systems
250 Crossways Park Drive
Woodbury, NY 11797
(800) 553-3332