Rich Acoustic 7B Speaker System Review

Rich Acoustic Labs’ Model 7B is a three-way floor-standing speaker system. Its 8-inch polypropylene woofer operates in a vented enclosure (with Thiele B-4 alignment) and crosses over at 790 Hz to a 2-inch soft-dome midrange driver in a separate compression chamber. The second crossover, at 4,500 Hz, is to a 1-inch soft-dome magnetic-fluid-cooled tweeter, which is surrounded on the front panel by a foam-plastic ring to improve dispersion and smooth the frequency response. All three drivers and the woofer port are vertically aligned. The crossover networks have 12-dB-per-octave slopes, use computer-grade components, and are phase-corrected.

The 7B system is housed in a handsome cabinet veneered in either white oak or American walnut. The cabinet’s edges and corners have rounded solid-wood moldings, and the whole exterior has a hand-rubbed finish. The dark-brown cloth grille is retained by plastic fasteners. Binding posts on 3/4-inch centers are recessed into the rear of the cabinet. The speaker has no external level or balance adjustments.

The Rich Acoustic 7B is 26 inches high, 11 inches wide, and 13 inches deep; it weighs about 40 pounds. Although the speakers can be placed directly on the floor, there are optional matching wood pedestals that raise them about 6 inches and tilt them slightly backward. Prices: speakers, $399 each; pedestals, $49.95 per pair.

Lab Tests

For our room-response measurements and listening tests, we placed the 7B’s on their pedestals and about 18 inches out from the wall behind them. The averaged response from the two speakers (driven one at a time) was measured at a single microphone position about 12 feet in front of the left speaker. The woofer response was measured separately at the cone and the port, using close microphone spacing to eliminate room effects, and the combined bass-response curve was spliced to the room measurement to form a composite frequency-response curve.

The combined bass response (woofer plus port) was impressively wide and flat, with a 5-dB overall variation from 20 to 1,000 Hz. The middle- and high-frequency portions of the room-response curve were equally impressive, uniform within 3 dB overall from 1,000 to 20,000 Hz, except for a minor jog at about 1,000 Hz (which could be a measurement artifact). The composite frequency response was flat within ±2.5 dB from 20 to 20,000 Hz, which is one of the best responses we have yet measured from a loudspeaker.

The axial FFT response, measured at 1 meter with our IQS system, was less constant, largely because of a dip at 2,000 Hz that might have come from a crossovercancellation effect (it did not appear in the room response). Nevertheless, the ±4.5-dB variation from 180 to 18,000 Hz was consistent with the uniformity of the room-response data.

The speaker system’s impedance was 6.5 ohms in the vicinity of 150 Hz, with maxima of 35 ohms at 58 Hz and 30 ohms at our lower measurement limit of 20 Hz. The impedance was a constant 8 to 9 ohms through the midrange and reached its minimum of just under 4 ohms at 7,000 Hz. An input signal of 2.83 volts of random noise at 1,000 Hz produced a sound-pressure level of 90 dB at a 1-meter distance, exactly as rated and fairly typical for ported systems of this size.

At a drive level of 2.83 volts, the woofer distortion was less than 1 percent between 60 and 100 Hz, rising smoothly to 3.4 percent at 50 Hz and 8.8 percent at 35 Hz. We measured the distortion at the port for frequencies below about 60 Hz, where the acoustic crossover between port and cone takes place.

We checked the power-handling ability of the 7B with single-cycle tone bursts at frequencies of 100, 1,000, and 10,000 Hz (each falling within the operating range of one of the three drivers). The drive level was increased until the acoustic waveform picked up by a microphone showed visible distortion or limiting, or until the amplifier output became distorted. At 100 Hz the woofer cone “bottomed,” producing a raspy sound, with about 250 watts input (based on the impedance of 8.5 ohms at that frequency). At 10,000 Hz the waveform distorted at about 335 watts (4 ohms).

It was difficult to determine the actual 1,000-Hz limits of the speaker, since the amplifier output became visibly nonsinusoidal at levels far below the actual clipping point, apparently because of an interaction between the speaker reactance and the amplifier at the frequency. The apparent power limit was 18 watts, but the actual limit is probably far greater since there was no audible hint of speaker distress even at much higher levels.

Comments

Little variety is possible in the external styling of a conventional box speaker, but the Rich Acoustic 7B manages to present an unusually handsome appearance by virtue of its attractively finished wood grain and rounded corners. Somewhat more latitude is available in the choice of drivers, port design, and crossover characteristics. Here too, Rich has set the 7B apart from most competitive speakers.

Listening to the 7B’s, our initial impression was one of smooth, wide, and generally uncolored sound with a slightly bright high end. Fortunately, the brightness was not in the middle or lower treble range, where it could have imparted stridency to the sound, but rather in the uppermost audible octave. Apparently the effect results from the system’s slightly elevated output in the 10,000- to 20,000-Hz range. Since much musical material lacks significant energy at those frequencies, this emphasis is not always evident. When it is, the sound is not unlike that provided by some moving-coil cartridges with similar rising high-end responses. The effect might best be described as an enhanced clarity or crispness, and we never found it at all unpleasant.

While it might not be wise to use these speakers with a cartridge that has a rising high-end response (the combination could make the highest frequencies too bright), programs coming from a flat, wide-range cartridge, tape deck, CD player, or FM radio sound just fine through the 7B’s. Their relative lack of midrange or bass coloration and their unusually extended bass response set them apart from many other box-shaped speakers in the same general price range. As always, it is advisable to audition the speakers, preferably in your own home, before buying them. But you are not likely to go wrong by choosing the Rich Acoustic 7B’s.

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