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Since its inception, Definitive Technology has specialized in bipolar loudspeaker designs. Bipolar speakers typically have duplicate groups of drivers, facing to the front and rear and driven in phase. That con figuration gives nearly omnidirectional response in the horizontal plane, with just a slight reduction in output to the sides at middle and high frequencies.
Bipolar speakers, when placed a few feet from the wall behind them, tend to add a quality of spaciousness to the sound, creating a somewhat more realistic soundstage than conventional speaker designs. In addition, the multiple drivers can handle more power than a standard configuration for a given distortion level (or, conversely, will generate less distortion for a given sound-pressure level).
Another potential benefit of the bipolar configuration is a narrower cabinet width, since low frequencies can be handled very effectively by two modestly sized woofers instead of a single larger one. That enables the de signer to use a smaller panel width for a given level of bass performance, minimizing the enclosure "footprint." But in the case of Definitive Technology's latest bipolar speaker, the BP 2000, the most distinctive (albeit virtually invisible) feature is a built-in powered subwoofer. The result is a reason ably compact speaker system with truly prodigious bass extension and out put capability. That is not to say that the BP 2000 is exactly a small speaker -- each one measures 50 inches high, 9 inches wide, and 16 inches deep and weighs an impressive 120 pounds -- yet it can be used effectively in al most any size room without visually dominating the decor.
Styled like most previous Definitive Technology bipolar speakers, the BP 2000 is a slender column covered with a black elastic "sock" over its full height on the front, sides, and about two-thirds of the rear panel. The top is a piano-finish, black-lacquered wood en plate that is easily removed for pulling down the cloth sock and exposing the drivers. The speaker's base is a similarly finished wooden plate.
The system is also available with cherry endcaps. For a tighter contact with the floor, optional spikes are available.
Although the BP 2000 is relatively tall and deep, side placement of the subwoofer driver enables the cabinet to remain as narrow as those of most other Definitive Technology speakers, and it occupies only about a square foot of floor space. If the speakers are slightly angled toward the listening position (for optimum stereo imaging), they are surprisingly inconspicuous. Lifting off the top plate and pulling down the grille sock reveals the driver complement. On the upper half of the front panel is a pair of 6¾-inch cone woofers (their effective cone diameter is about 5½ inches each) vertically flanking a 1-inch aluminum-dome tweeter in the popular D'Appolito configuration. The tweeter is offset slightly to one side of the panel's vertical midline, which may have been done as much to minimize the spacing between the woofers as for any imaging benefit. The woofers have cast magnesium baskets and compliant rubber surrounds.
The rear panel holds an identical trio of drivers, located directly behind the front array. Definitive Technology says the cabinet interior is divided into separate enclosure volumes that give the front and rear sections slightly different low-frequency cutoff frequencies, apparently to compensate for the closer proximity of the rear drivers to the wall. The rear tweeter is also off set, in the opposite direction from the front tweeter.
The lower half of the cabinet is devoted to the subwoofer and its 300 watt amplifier. The subwoofer itself is a massive 15-inch driver with an actual cone diameter of 13 inches, mounted on the side of the cabinet.
Designed as mirror-image pairs, the BP 2000 can be used with the sub woofers facing either outward or inward (the latter is recommended because of the slightly increased coupling between the two subwoofers).
Incidentally, when the speaker's top is removed and the cabinet edges exposed, you can see that the side holding the subwoofer is 1¼ inches thick, compared to 1 inch for the front and rear panels and 3/4 inch for the other side. A knuckle-rap test suggested that the structure is about as rigid as a brick or a cinder block. Although we could not see inside the enclosure, it is evidently strongly braced.
The bottom of the cabinet contains the subwoofer amplifier and its associated crossover components. Covering the bottom 15 inches of the rear of the enclosure is a metal panel with input connectors, amplifier heat sinks, a power switch, a line fuse, a sensitivity switch, and knobs for adjusting the bass equalization and level. Price is $3,000 per pair.
The BP 2000 offers a variety of connection options. It has three pairs of five-way binding posts (labeled HIGH, MID, and LOW), which accept single or dual banana plugs, wires, or lugs and are normally connected in parallel by gold-plated metal jumpers. The simplest connection uses only the wires that would normally connect your amplifier or receiver to conventional speakers. You can also bi-wire or tri-wire the speakers, with separate cables to each section, by removing the appropriate jumpers. Yet another possibility is to drive the subwoofer portion of the system from the line-level out puts of a preamplifier equipped with two sets of full-range line outputs (or Y adaptors could be used to turn each of a single set of outputs into two). Each speaker has a RCA phono-jack input to its subwoofer amplifier that can accept a full-range signal and pass it through the speaker's internal low-pass filter.
A twelve-page instruction manual describes the procedure for setting the subwoofer controls. The criteria for final adjustment are purely subjective, based on when it sounds "right" to you. In addition to the usual level control, there is a low-frequency equalization control for fine-tuning the balance between the low bass (under 50 Hz) and the upper bass (50 to 100 Hz). The procedure is not complicated, and the instructions point out that (as with separate subwoofers) there is no absolutely "correct" setting. You are encouraged to experiment with the settings to discover the one that best suits your own taste. Normally the subwoofers of the two speakers will be set identically, but the manual points out that you can compensate for asymmetrical positioning of the left and right speakers (which could affect their low-bass performance) by using different subwoofer level and equalization settings for them.
Although the speakers have sub woofer power switches, there is no problem in leaving them energized continuously, since they use very little power at idle (we never shut them off during several weeks of use). The heat sinks never became more than faintly warm, even after extended operation at high volume levels.
For the most part, we were able to test the BP 2000's as we do all speakers. The averaged room response of the left and right speakers, based on a swept warble-tone signal, was exceptionally uniform, with several minor ripples of less than 3 dB. That smoothness was verified by an MLS quasi anechoic measurement. Our measurements closely resembled the response curves supplied to us by Definitive Technology, which were made using a totally different procedure and in a very different environment.
All the response curves exhibited a series of small ripples, with a peak-to peak amplitude of 3 to 4 dB, across the range from 300 Hz to 20 kHz. Our close-miked measurement of the subwoofer's response agreed exactly with the manufacturer's data, including the effect of its equalizer control. In its middle position, which we used for listening and measurements, the subwoofer response was ±3 dB from 23 to 100 Hz.
In the range between 100 and 300 Hz, measurements become somewhat ambiguous, since there is an unavoidable interaction with the room boundaries. Our composite response curve for the BP 2000, combining the close miked subwoofer response and the room response, had a 6-dB peak-to peak variation between 100 and 200 Hz, which would certainly be different (but probably present to some degree) in any other room, The BP 2000's horizontal dispersion was typical of speakers with drivers of similar size. The output plots on-axis and 45 degrees off-axis remained close up to about 10 kHz, and then the curves diverged by about 5 dB at 13 kHz and 15 dB at 20 kHz.
The system's impedance ranged from 4 ohms between 3 and 20 kHz to 16 ohms at 20 Hz. There were peaks of 14 ohms at 100 Hz and 10 ohms at 1.4 kHz. The speaker's specifications state only that its impedance is compatible with amplifiers designed to drive 4- to 8-ohm loads, which is consistent with our measurements. There was no clear indication of the crossover frequency between the tweeters and midrange drivers in anything we measured or heard, which is actually as it should be.
The preliminary specifications for the BP 2000 include a 90-dB sensitivity rating, a bandwidth of 15 Hz to 30 kHz (!), and a recommendation for use with main system amplifiers rated between 30 and 300 watts per channel (which encompasses virtually every high-fidelity amplifier on the market).
We measured the system sensitivity at 1 meter with a 2.83-volt input of noise (equivalent to 1 watt into 8 ohms) as 92 dB sound-pressure level (SPL), slightly higher than rated. That suggests (and we verified) that the BP 2000 can be driven to lease-breaking levels by just about any receiver or amplifier, with a wide margin of re serve power. The main-system drivers had no difficulty handling all the power our test amplifier could muster in single-cycle tone bursts 860 watts at 1 kHz into the woofers and 1,280 watts at 10 kHz into the tweeters.
We measured the subwoofer distortion with a steady-state 2.25-volt input to the system (equivalent to a 90-dB SPL system output). The distortion (largely third-harmonic) was, to our surprise, not spectacularly low, ranging from 6 percent at 30 Hz to about 2 percent at 100 Hz and higher. It climbed steeply at lower frequencies, to about 18 percent at 20 Hz. That is not significantly different from what we have measured from some good conventional speakers that are smaller and less expensive than the BP 2000.
On the other hand, the BP 2000 can be driven to truly room-shaking levels in the low bass without much audible evidence of subwoofer (or any other) distortion. We measured average room levels (with musical program material) of close to 105 dB in some of our listening tests. As with any speaker, the ultimate proof of performance is in the listening. Over the years I have heard a few (very few!) speakers, usually at industry shows, that overwhelmed me and were clearly superior to almost any- thing else I had heard prior to that time. Without exception, those speakers were far more expensive (by a factor of many times), and usually much larger, than the BP 2000. I never had the opportunity to live with those speakers and listen to them at length with material of my own choosing, and the specific program material plays an enormous role in one's listening impressions.
The Definitive Technology BP 2000 is the first speaker I have been able to audition in my own familiar surroundings that has given me that special thrill that usually costs ten or more times its price to obtain. When I heard it demonstrated at the 1995 Winter Consumer Electronics Show (CES) in Las Vegas, I knew it was something special, and the more I listen to it now the more that feeling is confirmed.
For one thing, driven by even a modestly powered amplifier, it can play louder than I can imagine anyone would normally want to listen, yet without audible distortion. This speaker is just loafing along at any level one would reasonably use in a home. The bipole configuration generates a pleasingly natural stereo stage, and the sub woofers provide a foundation that you can feel as much as hear.
Frankly, if circumstances allowed, I would choose these speakers for my self. Alas, space and decor considerations make that impractical. And I hate to pass up a bargain like this one! Consider what you get for $3,000: two first-rate bipolar speakers, two 15-inch subwoofers, and two 300-watt amplifiers, all packaged in two attractively styled columns that occupy one square foot each of floor space.
I doubt that you can get a better sounding system for less than several times the price of the BP 2000. And one more thing: You don't need exotic equipment to get high-caliber sound from a pair of BP 2000's. The speaker was demonstrated at CES with very high-end cables and amplifiers. I used a 75-watt receiver and 14-gauge Radio Shack speaker wire, and I doubt that an additional $20,000 spent on that end of the system would have made any appreciable improvement. The BP-2000 is, price notwithstanding, a remarkable value.
Definitive Technology, Dept. SR, 11105 Valley Heights Dr., Baltimore, MD 21117
Source: Stereo Review (09-1995) by Julian Hirsch
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