Definitive Technology BP10B Definitive Technology has hit the bull’s eye, Lab Tests, Comments

TEST REPORTS

“Definitive Technology has hit the bull’s eye.”

rounds and dustcaps, high-temperature voice coils, and massive magnet struc- tures. The fabric-dome tweeters have dual air chambers, one behind the dome and the other connected to the first chamber by a hole through the pole piece, behind the magnet structure. Definitive Tech- nology says that the dual chambers lower the tweeter’s resonance frequency, extend its frequency response, and reduce dis- tortion. An aluminum voice coil, high- temperature wire, and ferro-fluid damping enhance the tweeter’s power-handling ability.

The BP10 has a rated frequency re- sponse of 20 to 28,000 Hz, a nominal im- pedance of 6 ohms, and a sensitivity spec- ification of 89 dB. It is recommended for use with amplifiers rated between 20 and 300 watts per channel.

Lab Tests

We installed the Definitive Technology BP10 speakers about 12 inches in front of a wall, 7 feet apart, and 4 to 5 feet from the side walls of the room. They were an- gled a few degrees inward for best im- aging at the preferred listening position.

“Our measurements showed the Definitive Technology BP10 to be an excellent speaker…”

The composite frequency response—a combination of the averaged room re- sponse of the two speakers at a single mi- crophone position and a close-miked (ef- fectively anechoic) measurement of the woofer response—was notably smooth and free from irregularities between 1,000 and 20,000 Hz, varying less than ±2 dB over the range. The bass response com- bining the outputs of the drivers and the port (corrected for their relative dimen- sions) was within ±2 dB from 40 to 800 Hz. The combined curves overlapped for more than an octave, with a slight dip of 3 to 4 dB centered at 1,000 Hz (which may have been a measurement artifact). The smooth bass and midrange output (be- tween 50 and 700 Hz) averaged about 3 dB higher than the output above 1,500 Hz. The overall response variation was only ±3.5 dB from 25 to 20,000 Hz. Even at 20 Hz, the output was down a mere 5 or 6 dB from the average level at higher fre- quencies.

A quasi-anechoic FFT response meas-

urement confirmed the overall shape of

the speaker’s frequency-response curve,

which sloped downward smoothly by

about 4 or 5 dB from 700 or 15,000 Hz.

Above 15,000 Hz, the on-axis response

fell off linearly to about -14 dB at 28,000 Hz.

The difference between an on-axis fre- quency-response measurement and one made 45 degrees off-axis was negligible below 10,000 Hz. At higher frequencies, the two response curves diverged, with a typical difference of about 12 dB up to about 17,000 Hz. The group delay was constant within ±0.1 millisecond from about 3,000 to 25,000 Hz. Even in the woofer range, the delay remained less than 1 millisecond down to about 200 Hz.

“The two small woofers not only reached down to the lowest musical frequencies, but they did so with surprisingly low distortion.”

The system’s minimum impedance of

3.5ohms occurred at 200 Hz. Impedance was 4 ohms at 35 Hz and 4.5 ohms from 5,000 to 10,000 Hz. The maximum was 8 ohms at 65 and 900 Hz. The phase angle of the impedance was less than 22 degrees over the full 20- to 20,000-Hz range.

The BP10 generated a 90-dB sound- pressure level at 1 meter with an input of

2.83volts of pink noise. At 1,000 and 10,000 Hz, our amplifier clipped (at 850 and 1,100 watts, respectively) before the speaker drivers were overloaded by a sin- gle-cycle high-power pulse. At 100 Hz, however, the woofer cone reached the lim- its of its suspension excursion at an input of 150 watts into a 4.7-ohm impedance.

The woofer distortion, with 2.83 volts input, was between 0.3 and 0.4 percent from 150 to 800 Hz. It increased smoothly at lower frequencies to 1 percent at 100 Hz and 1.6 percent at 80 Hz. The effective crossover frequency between the cone and port output was 75 Hz, where the dis- tortion was about 2 percent from each source. The port distortion remained less than 2 percent down to 43 Hz, reaching 5 percent at 30 Hz.

“…the BP10 proved to be all that was claimed for it.”

Comments

Our measurements showed the De- finitive Technology BP10 to be an ex- cellent speaker by any normal standards of performance. Not only did it have a smooth, flat frequency response, good dis- persion, and very little evidence of cabinet diffraction or resonances, but it delivered an impressive amount of clean bass from its two small drivers.

As I have often pointed out, speaker measurements are but a part of the story. The final proof of performance lies only in the listening, and that was where the BP 10 proved to be all that was claimed for it. This slender, inconspicuous black box de- livered an effortless, seamless sound es- sentially free of spurious emphasis (or de- emphasis) of any part of the spectrum.

The two small woofers not only reached down to the lowest musical fre- quencies, but they did so with surprisingly low distortion. Side by side with some other speakers twice its size, the BP10 managed to hold its own (or better) in practically every comparison. The other speakers were somewhat more expensive than the BP10, and, naturally, they sound- ed slightly different (which would be true of any speakers one might compare in this manner), but they and the BP10 were in- arguably peers.

The BP10’s imparted an excellent sense of space, probably in good measure a re- sult of their rear-radiating drivers, whose output reflects from the wall behind them. These spatial properties were well dem- onstrated by the Chesky “Jazz Sampler, Vol. 1,” a CD that has an interesting im- aging test track. Short bursts of random noise pan between the left and right speak- ers and also go up, across, and down to the other speaker. Some speakers fail to reproduce the appearance of up/down travel, whereas others, like the BP10, con- vey the sensation in a surprisingly ef- fective manner.

“…a truly outstanding speaker system.”

Another point in favor of the BP10 is its relatively unobtrusive size and styling. Its shape makes it suitable for service as a pedestal supporting a small vase or sculp- ture. Since there is little in its appearance to suggest its function to a nonaudiophile, the BP10 could add an attractive dec- orative feature to a room while serving at the same time as a truly outstanding speaker system.

It appears that Definitive Technology has hit the bull’s eye squarely with its in- itial product. The BP10 is an innovative solution to the problem of providing true high-fidelity sound from attractive and reasonably sized speakers at an affordable price.

11433 Cronridge Drive, Owings Mills, MD 21117

(410) 363-7148

Reprinted with permission from the February 1991 issue of STEREO REVIEW magazine. Copyright © 1991 by Hatchette Magazine Inc. All Rights Reserved.