Polk Audio RM7000 Speaker System Review
Polk Audio has, for some time, been making three-piece speaker systems consisting of a pair of small satellite speakers and a separate bass module-an increasingly popular format on today's audio scene. In the RM7000, the company has both extended the concept and carried it to a new level of performance. The RM7000 consists of two RM2000II satellites for the left and right channels, a new acoustically matched center-channel satellite, and a newly designed powered bass module, the PSW100.
The RM2000II satellite (also available separately) is a compact speaker with a 3-1/2-inch cone low-frequency driver in a sealed enclosure and a 3/4-inch dome tweeter. The drivers are "time aligned," with the tweeter stepped back about 1-3/4 inches from the woofer. The cabinet, available in white or black (actually a white-speckled dark gray) is molded of a dense polymer with a smooth finish that has the look and feel of polished marble. Rated frequency range for these satellites is 150 Hz to 20 kHz. The center speaker, which is styled and finished to match the main satellites, uses two cone drivers and one tweeter, identical to those in the other satellites.
The system's PSW100 bass module features Polk's new High Velocity Compression Drive (HVCD) bandpass enclosure, designed for high efficiency. Polk says its performance equals or exceeds that of larger competitive products. It uses a single, heavy-duty 8-inch woofer driven by a built-in 65-watt amplifier. It also contains an electronic crossover network (continuously adjustable from 50 to 150 Hz) and a level control. Illustrations on the module's control panel show the recommended settings for use with different Polk speakers, including the satellites in the RM7000 package.
The bass module is relatively compact and can be placed almost anywhere in the room, even within a piece of furniture. Sound emerges from it through a circular port in its underside, about an inch above the floor, and propagates in all directions. Like the three satellites, the PSW100 is magnetically shielded and can be placed close to a video display without affecting the picture.
The satellites can be placed on stands or furniture following the guidelines in the system instructions. Additional flexibility is provided by wall-mounting brackets. Adding another pair of RM2000II satellites to the RM7000 system converts it to a full-fledged, fully matched surround system. Although we tested the RM7000 primarily as a four-piece stereo system, we also had a pair of RM2000II's at the back of the room for evaluation in surround mode.
We measured system performance following our usual procedures. The three satellites were placed across the front of the room, with the PSW100 on the floor next to the left speaker.
The left and right satellites were on 30-inch pedestals, the center on a shelf about 5 feet high midway between.
We measured the room response of the left and right satellites with a swept-frequency sine-wave signal, averaged for the two channels. The bass unit's output was measured separately, with the microphone at its exit port, at three crossover settings-50, 80, and 150 Hz. Splicing the satellite response curves to the PSW100 curve (using the 150-Hz crossover setting, which was recommended for this combination of components) produced a relatively flat, wide-range composite curve. There was a distinct notch in the combined curve between 100 and 300 Hz, but it was not audible and appeared to be an artifact of the PSW100's placement and our measurement technique.
Aside from that anomaly, the system's composite response was within ±4 dB from 33 Hz to 20 kHz. Such extended bandwidth is unique in our experience for an affordably priced subwoofer/satellite system. Listening tests confirmed that output remained strong and useful down to the low 30-Hz range. The PSW100's frequency response was an impressively flat ±2.5 dB from 35 to 130 Hz at the highest crossover setting (150 Hz). As the control was turned down, the output at or below 40 Hz did not change, but the higher frequencies were rolled off at a gradually increasing rate.
Quasi-anechoic (MLS) frequency-response measurements of the RM2000II satellite showed an output variation of only ±3 dB from 300 Hz to 13 kHz on the speaker's axis. Above 13 kHz there were some narrow-band variations that suggested a driver-diaphragm resonance, possibly in combination with the grille (there were minor differences between the response curves with and without the grille in place). The tweeter's high-frequency dispersion was typical of Vi-inch dome drivers, with the output 30 degrees off the forward axis rolling off above 10 kHz to about -8 to -10 dB at 20 kHz. The RM2000II had an excellent group-delay characteristic, with less than 1 millisecond peak-to-peak variation from 150 Hz to 20 kHz.
The impedance curves for the left/right and center satellites were generally similar because of their common driver complement (the two cone drivers in the center speaker operate in roughly twice the volume of the other satellite enclosures). Minimum impedance of a left/right satellite was 4 ohms at 600 Hz, and a reading of 8 ohms (at the same frequency) for the center speaker indicated that its two low-range drivers were connected in series. The distortion in the output of an RM2000II, delivering a 90-dB sound-pressure level (SPL) at 1 meter, was 2 percent at 150 Hz, falling to 0.3 percent between 500 and 800 Hz.
Listening to the RM7000 system (with and without the surround speakers) confirmed its excellence. Considerable experience with subwoofer/satellite speaker systems has given me a good sense of their strengths and weaknesses, and this Polk system is amply endowed with the former and has practically none of the latter. Personally, I find good sub/sat systems (and this one is very good indeed) to be an ideal solution to the problem of fitting a music (or home theater) system into a room that cannot be dedicated exclusively to that function. Such a system can give a very high return in enjoyment for a relatively modest investment.
But there are significant differences among sub/sat systems (as among all sorts of speakers). One of the major differences is in their low-frequency performance. It takes more than a black box with one or two drivers inside it to generate clean, low bass that merges seamlessly with the sound from several smaller speakers. Fortunately, thanks to the difficulty we have in localizing low-frequency sound sources (say, below 100 Hz or so), many sub/sat systems manage to deliver a satisfactory illusion of a continuous frequency spectrum and stereo image.
The results may be, and frequently are, quite satisfactory. Few sub/sat systems (few speakers of any kind, for that matter) can produce much output in the bottom octave, however. And once you have heard really low bass, below about 50 Hz, you will be less willing to settle for a pale imitation. The Polk RM7000 delivered clean, palpable bass down to about 30 Hz in our room and might do even better in another room or with corner placement (we had no comers available).
It all adds up to a truly first-rate system for a very reasonable price. As with any good sub/sat speaker system, the sound gave no hint of its divided audio personality. And the RM7000 seemed adept at reproducing whatever material we fed to it, whether regular two-channel stereo or, with two more RM2000II satellites near the back of the room, full surround sound.