B&W DM2000 Speaker System Review

The B&W DM2000 is part of the “Digital Monitor” series from this highly respected British speaker manufacturer. It was designed to provide the same smooth, linear response as the company’s professional monitor speaker, the Model 801, in a smaller and less expensive version more suited to home use. The DM2000 is a two-way, three-driver system. The bass and midrange frequencies are handled by a newly designed 7-inch woofer and a passive Acoustically Driven Radiator (ADR) of the same size. Frequencies above 3,000 Hz are radiated by a 1-inch dome tweeter.

Much effort went into achieving an overall time-coherent sound radiation— sometimes referred to as “linear phase”—from the DM2000 without resorting to the physically awkward stepped driver configuration used in some earlier linear-phase speakers from B&W and other manufacturers. An electronic time delay (ETD) circuit is built into the DM2000’s crossover-network system. The crossover filter proper is a fourth-order Butterworth design with steep, 24-dB-per-octave slopes in the stop-bands. This filter provides a smooth amplitude transition in the crossover region, but its phase characteristics introduce a small time delay between the two drivers. Instead of physically shifting the tweeter backward to compensate for this time delay and the one resulting from the different acoustic path lengths to the drivers, B&W added an “all-pass” network to the crossover system. This has a flat frequency response but with a phase shift equivalent to the necessary time-delay correction. The overall result is a linear-phase speaker system with all its drivers mounted in the same plane on a conventional vertical, flat front panel.

Like all B&W drivers, the DM2000’s woofer is of the company’s own design and manufacture. It features a specially shaped plastic-impregnated cone made of Kevlar (a synthetic fabric having a high ratio of stiffness to mass and good internal damping) driven by a voice coil that is capable of withstanding temperatures of 250°C or higher. Another feature of B&W professional monitor speakers that was carried over into the DM2000 is an audio-signal-powered overload circuit (APOC) that instantly cuts off the drive units if a very high level threatens to damage them; it simultaneously lights an LED on the front of the speaker enclosure.

The wood cabinet of the B&W DM2000, available veneered in walnut, rosewood, or black ash, is 32-1/4 inches high, 12-1/4 inches wide, and 15-3/4 inches deep. It has a five-sided cross section (to reduce internal standing-wave reflections) with the two rear panels forming a right angle. Although this might suggest a corner placement, the speaker is intended for a conventional free-standing installation away from a rear wall.

The top of the cabinet is covered by a molded brown plastic plate. The drivers are close to each other and vertically aligned as near as possible to the top of the front panel. The enclosure is sealed, and the binding-post terminals are in a cutout “stepped” section at the bottom rear of the cabinet. There are no level or balance, adjustments. The brown cloth grille, stretched on a metal frame, is retained by plastic snaps. The system weighs 55 pounds. Price: $650 each in walnut or black ash, $925 in rosewood.

Laboratory Measurements

The axial frequency response of the B&W DM2000, measured with our IQS FFT analyzer, was impressively flat and wide. From 180 to 19,000 Hz, it varied a total of 5 dB (±2.5 dB), but much of that was in the lower frequency portion. From 900 to 18,000 Hz, the total variation in output was only 3 dB, and in the upper part of the tweeter range, from 9,000 to 17,000 Hz, the output was flat within 1 dB overall! Even in the ultrasonic range, the output remained strong and smooth. The overall response from 180 to 30,000 Hz was within ± 5 dB.

Of course, a flat response on the speaker axis is not sufficient for high-quality sound; the dispersion at high frequencies must also be reasonably broad. From 1,000 to 20,000 Hz, the DM2000’s response curves measured on axis and 45 degrees off axis were within 6 dB of each other, and only above the audible frequency range did they diverge substantially. The good phase response implied by this smoothness was confirmed by the group-delay figures, which varied only 0.2 millisecond (ms) from 5,000 to 23,000 Hz and 0.5 ms from 180 to 20,000 Hz.

We separately measured the bass frequency response close to the woofer and ADR cones, then combined the two. The overall bass response was within ± 3 dB from approximately 25 to 180 Hz, with the ADR’s output predominating below 35 Hz. The measured sensitivity of the DM2000 at 1,000 Hz was an 86-dB sound-pressure level (SPL) at 1 meter with a drive level of 2.83 volts (very close to the rated 87 dB). When we measured the bass distortion at an input of 4.5 volts (equivalent to a midrange output of 90 dB), the distortion was outstandingly low, less than 1 per cent down to 40 Hz and rising only slightly to about 2 per cent at 30 Hz. The system impedance was a minimum of 6 ohms at 150 Hz and remained between 6 and 15 ohms from 66 to 20,000 Hz. At the low-frequency resonances of 24 and 54 Hz, the maximum impedance ranged from 30 to 35 ohms.

While the “Digital Monitor” designation for the DM2000 might refer to its exceptionally wide and smooth frequency response or its linear-phase characteristics, it can also apply to its built-in protection against damage from high peak program levels. We checked this last characteristic with short-duty-cycle tone-burst signals, watching the acoustic output of the speaker on an oscilloscope for signs of distortion or overload. At 1,000 Hz, in the upper end of the woofer/midrange driver’s operating range, the amplifier output clipped first, at roughly 800 watts, with no signs of speaker overload. At 10,000 Hz, in the tweeter’s operating range, a peak input of 700 watts did not distress or damage the speaker. Only in the bass range, at 100 Hz, could we clearly establish the power limitation of the DM2000, since the woofer cone and voice coil “hit their stops” with an audible rasping noise at about 400 watts.

Comment

Measurements aside, simply listening to the B&W DM2000 left no doubt of its distinguished heritage. While it certainly did justice to the Compact Discs at our disposal, it was equally satisfying with LP records and with FM broadcasts. First and foremost, its sound was smooth and uncolored (hardly surprising in view of its measured performance), with an absence of lower-midrange coloration on voices, both male and female, that set it apart from most speakers heard in our listening room. Second, even at the lowest listening levels, the deep bass was literally palpable. The sound actually gave the impression of being aided by a subwoofer, which is quite surprising in view of the rather small size of the speaker’s bass-radiating surfaces.

Although we played music quite loud on occasion, the speaker’s LED never flashed to show that the protection circuit had operated. Considering the ability of the system to absorb high power levels, and the fact that our listening amplifier had a maximum output of “only” 200 to 300 watts, we probably never reached the speaker’s limits when we played music.

A number of excellent speakers are available in the price range of the B&W DM2000, and no doubt each has its adherents. For our part, we thoroughly enjoyed our all-too-brief exposure to these fine speakers and hated to return them. To us, they demonstrated unambiguously the sonic effectiveness of a combination of expert theoretical knowledge, high-technology engineering and manufacturing, and just plain good taste. As we see it, these were the basic ingredients in the recipe for creating this superb speaker system.

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