Infinity RS3000 Speaker System Review

The Infinity RS series of speakers has been designed to provide some of the essential qualities of the higher-priced Infinity speakers in more affordable packages. In 1978, Infinity pioneered the use of polypropylene cones for its woofers because the company found that polypropylene’s self-damping properties enabled cones made of it to provide audio reproduction superior to that of paper cones. All current Infinity speakers, including the RS series, use polypropylene woofer cones. The RS3000, next to the top of the RS series, is a two-way system whose 8-inch woofer crosses over at 4.000 Hz to a 1-inch Polycell dome tweeter. The dome of this proprietary Infinity driver, made of polypropylene foam, is said to provide extremely good transient response and a high-frequency limit beyond 22.000 Hz.

The rated frequency response of the RS3000 is 45 to 22,000 Hz ± 3 dB. Its nominal impedance is 6 ohms, and its sensitivity is 89 dB sound-pressure level (SPL) measured at 1 meter. The speaker is recommended for use with amplifiers rated between 20 and 100 watts per channel. The RS3000 woofer operates in a sealed cabinet, which has an attractive oak finish on all surfaces except the rear. The front edges are rounded to reduce diffraction effects and improve imaging. The black grille-cloth frame snaps into plastic sockets that hold it about 1/2 inch away from the speaker board. The cabinet is 20-3/4 inches high, 12 inches wide, and 10-1/4 inches deep. Each speaker weighs approximately 23 pounds. Price: $298 per pair.

Lab Tests

The RS3000’s impedance measured 4 ohms at its minimum point, from 130 to 180 Hz, and a maximum of 32 ohms at the 55-Hz bass resonance. The nominal 6-ohm rating appears to be close to its typical impedance throughout the audio range. The measured sensitivity was 89.5 dB SPL, almost exactly matching its rated value.

Mounted on 26-inch-high stands, as recommended, the two RS3000’s produced very similar room-response curves (measured on the axis of one speaker and about 30 degrees off the axis of the other). The close-miked woofer response had a broad maximum in the 60- to 150-Hz range and sloped off gently by about 5 dB at 1,400 Hz. The bass output dropped at 12 dB per octave below 60 Hz. We measured the woofer distortion with a constant drive level of 3 volts (equivalent to a 90-dB SPL at 1 meter). It varied between 0.6 and 1.8 percent from 100 Hz to 60 Hz, rising to 5 percent at 48 Hz and 10 percent at 35 Hz.

When we spliced the woofer curve to the room curve, the result was a slightly upward-sloping but quite smooth overall response from 500 to 20,000 Hz, with a total level change of about 5 dB. The low-frequency portion of the curve sloped downward by the same amount from 100 Hz to the minimum point at 500 Hz (the response in this range is a function of speaker placement and room characteristics). The ± 3-dB response variation from 45 to 20,000 Hz (our upper measurement limit) not only matches the speaker’s ratings but represents excellent performance for such a small, inexpensive speaker. Our quasi-anechoic FFT measurements showed a moderate amount of response fluctuation, about 6 dB overall from 180 Hz to 20,000 Hz, which generally agreed with our other data.

The horizontal dispersion of the RS3000 was good. The response measurements on-axis and 30 degrees off-axis fell within 5 dB of each other over virtually the whole range up to 10,000 Hz, diverging above that point. The phase response was very good, especially in the Polycell dome tweeter’s operating range. The group delay varied only 0.2 millisecond overall between 4,000 and 20,000 Hz, and it remained within 0.5 millisecond down to about 500 Hz.

In pulse-power tests, the woofer “bottomed” with an input of 255 watts at 100 Hz into its 4.5-ohm impedance. At higher frequencies, however, the amplifier clipped before the speaker reached its limits. At 1,000 Hz (still in the woofer range), the amplifier was able to deliver 320 watts to the 12-ohm load, and at 10,000 Hz (in the dome tweeter’s range) it reached 410 watts into 8.8 ohms.

Comments

Although no frequency-response measurements can describe the sound of a speaker except in the most general terms, it would be unlikely for anything to be seriously wrong with the sound of a speaker that measured the way the Infinity RS3000 did. In fact, it sounded clean and musical, though with a distinct brightness that somehow seemed inconsistent with its measured properties.

We could find nothing in our measurements to explain this effect. Thinking that the cause might actually be a bass deficiency (the speaker’s bass did not seem to sound as strong as its woofer-response curve would imply), we placed the speakers on a shelf against the wall to reinforce the lower frequencies. The bass enhancement was indeed beneficial, and we felt that the overall sound quality was improved, but the treble brightness remained. It was never objectionable, and we would not have been concerned about it except for the flatness of the measured response. Possibly a more absorbent room would have soaked up enough high-frequency energy to eliminate the brightness.

In all, however, the Infinity RS3000 proved to be a good speaker, as well as an excellent value. It is unusual for a $150 speaker to have the wide, smooth response that this one demonstrated, and we have seen many larger and costlier systems that could not match its performance.

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