Definitive Technology BP10B User manual

EFINITIVE TECHNOLOGY’S
first product is an unusual loud-
speaker that offers exceptional
performance for its size and
price. The BP10 is a slender columnar speaker
measuring 42 inches high, 9 inch-
es wide, and 11 1/2 inches deep and
weighing about 60 pounds. Its exterior is
completely black, and the four sides are
covered by a fabric sleeve that fits snugly
around the enclosure. The wood base and
top plate have a glossy lacquer finish. The
top cap is also available in solid oak. The
gold-plated, multiway terminals, which
accept dual banana plugs, are under the
Stereo Review
TEST REPORTS
D EFINITIVE T ECHNOLOGY BP10 B IPOLAR S PEAKER S YSTEM
“...a truly outstanding speaker system.”
Julian Hirsch, Hirsch-Houck Laboratories
D
base, with a slot for the connecting cable.
There is no visible indication of the
number, size, or configuration of the driv-
ers. Actually, the BP10 is a bipolar system
(hence the “BP” designation) containing a
pair of identical two-way speakers. One
faces forward conventionally, and the oth-
er is on the rear panel, facing backward.
Each consists of a 6 1/2-inch woofer and a
1-inch dome tweeter, with the woofer lo-
cated at the top of the cabinet and the
tweeter just below it.
Since the front and rear halves of the
system radiate in phase over their full fre-
quency range, their bass outputs augment
each other. In this respect, the BP10 is un-
like dipole radiators such as large electro-
static speakers or similar planar systems
in which the front and rear surfaces radi-
ate out of phase and tend to cancel each
other at low frequencies. Another result of
the BP10’s bipolar design is that it oper-
ates best placed about 8 to 12 inches out
from a wall—unlike planar systems,
which must normally be placed several
feet away from a wall.
The BP10’s two woofers share a com-
mon enclosure vented by a single ducted
port at the bottom of the rear panel. Ac-
cording to the manufacturer, the bass-
tuning system was computer-designed to
duplicate the loading of a transmission-
line system in respect to its bass response
and transient behavior while retaining the
advantages of a simpler and less ex-
pensive cabinet.
There was no skimping on the design of
the cabinet, however. Its sides are made of
3/4-inch particleboard, with front and rear
panels of 1-inch-thick Medite (a highly
rigid composition material) and extensive
internal bracing. The cabinet’s rounded
edges and narrow profile, plus its frame-
less cloth grille “sock,” are designed to
minimize diffraction, which can impart a
boxy coloration to the sound and mar the
spatial imaging.
If it becomes necessary to replace a
driver or perform other internal servicing
of the speaker, lifting the top plate reveals
the drawstring that keeps the grille snug to
the cabinet. After the drawstring is loos-
ened, the grille can be slipped down or re-
moved for access to the drivers or the
crossover network. The designers chose a
fourth-order Linkwitz-Riley network to
give the BP10 uniform response in the
crossover region as well as optimum
phase and transient response. The cross-
over frequency is not specified, but our
measurements suggest that it is in the vi-
cinity of 2,000 Hz.
The BP10 uses rugged, high-quality
drivers. The woofers have cast-
magnesium baskets, mineral-filled homo-
polymer cones with butyl rubber sur-
“Definitive Technology’s
first product is an unusual
loudspeaker that offers
exceptional performance…”
Latest BP10B speaker
is even better

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.
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 system’s minimum impedance of
3.5 ohms 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
2.83 volts 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.
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.
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.
TEST REPORTS
11433 Cronridge Drive, Owings Mills, MD 21117
[phone]
“Definitive Technology has hit the bull’s eye.”
“Our measurements showed
the Definitive Technology
BP10 to be an excellent
speaker…”
“…the BP10 proved to be all
that was claimed for it.”
“…a truly outstanding
speaker system.”
Reprinted with permission from the February 1991 issue of STEREO REVIEW magazine. Copyright © 1991 by Hatchette
Magazine Inc. All Rights Reserved.
“The two small woofers not
only reached down to the
lowest musical frequencies,
but they did so with
surprisingly low distortion.”