Infinity RS6 Speaker System Review

Much of the advanced technology employed in the $35,000 Infinity Reference Standard speaker system has now been applied to the more affordable speakers in Infinity’s Reference Standard series, of which the RS6 is the least expensive floor-standing model. The RS6 is a compact three-way speaker that measures 22 inches high, 13-1/2 inches wide, and 10 inches deep and weighs about 28 pounds. The vertical front edges of the cabinet, veneered in oak, are curved to reduce diffraction effects that can modify a speaker’s polar response.

The drivers of the Infinity RS6 are all somewhat unconventional. The 8-inch woofer, operating in a sealed enclosure, has a cone of clear polypropylene, said to be superior to paper in its high stiffness, low mass, and resistance to temperature and humidity changes. At 600 Hz there is a crossover to a “Polydome” midrange driver, a 2-inch-diameter polypropylene dome driven at its outer circumference by a voice coil of the same diameter. This driver is said to derive the same benefits as the woofer does from its polypropylene construction. A perforated metal grille just behind the transparent dome protects it from damage caused by external physical pressure without affecting its forward radiation. The second crossover, at 4,000 Hz, is to an electromagnetic induction tweeter, or EMIT, which employs a planar plastic diaphragm, with extremely low mass, on which a rectangular pattern of conductors is deposited. The diaphragm is mounted in a powerful magnetic field generated by samarium cobalt magnets. It radiates sound through four vertical slits in a metal plate.

The three drivers of the infinity RS6 are mounted in a vertical line. A black cloth grille, retained by plastic snaps, covers the front of the speaker. Although the RS6 is meant to be operated vertically, it can also be mounted horizontally on a shelf. In this position, the tweeter can be rotated (after removing the four mounting screws with a screwdriver) by 90 degrees to preserve its wide horizontal dispersion. For floor mounting, it is suggested that the speakers be raised slightly from the floor and tilted back so that the tweeters point toward the listener’s ear level. Infinity manufactures an optional 8-1/2-inch-high wooden pedestal base for that purpose. Twin binding-post connectors, spaced 3/4 inch apart, are recessed into the rear of the cabinet, together with a fuse holder and small knobs for the continuously variable tweeter and midrange level adjustments. The RS6, which is recommended for use with amplifiers rated between 35 and 100 watts per channel, has a rated nominal impedance of 4 to 8 ohms and a rated frequency response of 45 Hz to 32 kHz, ±3 dB. The price of the Infinity RS6 is $259.

Laboratory Measurements

We used the Infinity RS6 speakers on their pedestals for both testing and listening. The speakers were positioned about 2 feet from the wall behind them, and the midrange and tweeter level controls were set to maximum. The averaged room response curve was, for the most part, very flat and smooth. It did, however, show a 6-dB midrange dip, between 500 and 1,000 Hz. This measurement was made with the microphone near the rear of the room, some 12 feet from the speakers, and very similar effects were noted on both speakers (in a normal stereo configuration, but measured singly).

The FFT (quasi-anechoic) frequency response, measured 1 meter from the front of the speaker, showed a midrange drop of about the same magnitude, but at 1,500 Hz. It also yielded the widest, flattest frequency response we have yet measured from a speaker, varying about ±4 dB from 180 Hz (the lowest frequency of this particular measurement) to 27,000 Hz. From 12,000 to 25,000 Hz, the output varied only ± 1 dB (2 dB overall)! Even at 45 degrees off the speaker’s axis, the response did not change significantly below 15,000 Hz (except for a single narrow dip in the 5,000- to 6,000-Hz region).

The closed-miked woofer response reached a maximum at 100 Hz, about 4 dB higher than the plateau from 250 to 450 Hz, and dropped off rapidly above 500 Hz, presumably due to the crossover network. The low-frequency response fell at 12 dB per octave below 70 Hz. When we spliced this curve to the middle- and high-frequency room response curve, the combination showed the midrange dip mentioned earlier. Close-miked FFT measurements of the midrange driver response showed a drop below 1,000 Hz, suggesting that the dip might be a real one caused by a crossover gap. We could not hear the gap as such, and its importance on our response plots was exaggerated by the extraordinary smoothness of the speaker’s response over the rest of its operating frequency range. Because of the limitations inherent in combining a room response measurement with an essentially anechoic measurement, the composite frequency response was not as flat as would have been expected from our FFT measurements. Even so, its ±6.5-dB variation from 30 to 20,000 Hz is certainly creditable performance for any speaker.

The midrange level control affected the output between 1,000 and 3,000 Hz, with a maximum reduction of about 6 dB. The tweeter control range was about 7 dB, starting at about 6,000 or 7,000 Hz. The flattest response (and best sound, to our ears) was obtained with both controls at maximum. The speaker’s phase-shift characteristics were excellent, with a group-delay variation of less than 0.2 millisecond from 1,000 to 20,000 Hz.

The sensitivity of the Infinity RS6 was about average for a compact system operating in a sealed enclosure. Its acoustic output in the midrange was 87.5 dB at a 1-meter distance with an input of 2.83 volts. The woofer distortion was measured with a constant input of 3.76 volts, corresponding to a midrange output of 90 dB. It measured between 1.5 and 2.5 per cent from 100 to 48 Hz, increasing to 7.5 per cent at 40 Hz and 20 per cent at 30 Hz. The system impedance dipped to 4 ohms between 100 and 150 Hz, and it reached its minimum of 3 ohms at 2,200 Hz, with peaks of 20 ohms at 50 Hz and 30 ohms at 750 Hz. We would consider this to be a 4-ohm system from the standpoint of amplifier loading.

Comment

The Infinity RS6 sounded every bit as good as it measured, with a smoothness, transparency, and overall clarity that seemed almost inconsistent with its modest price. The midrange “hole” was never audible to us. However, the smooth, widely dispersed output of its tweeter was audible: there was an overall sense of air and space surrounding the music that was clearly discernible in A-B comparisons against other very fine speakers whose tweeters lacked the dispersion and extremely wide-range response of the EMIT radiator. It was interesting to observe the improved high-frequency clarity, probably attributable to the extended high-frequency response of the tweeter, in A-B comparisons with some other loudspeakers whose highs were flat to 15,000 Hz but fell off at higher frequencies.

In its literature, Infinity makes a point of the spatial qualities of the Reference Standard speakers. We must agree that, for whatever reason (probably a combination of several factors), the RS6 produced a strikingly open sound stage in our listening room. We listened to a number of digital Compact Discs with these speakers, and the combination was a happy one.

The Infinity RS6 represents, in our view, an exceptional combination of tasteful styling and superior performance at a bargain price. There are many good speakers in its price class, but in sound quality this one seems to be a pace setter.

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