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Sounding Board
Definitive Technology's Sandy Gross on Loudspeaker Design
The Case for Bipolar Loudspeakers with Built-in Subwoofers
C
hris Martens recently reviewed the Definitive Technology BP7001
SuperTower for The Absolute Sound (Issue146). During the review process, I
discussed with him at some length two of Definitive's signature technolo-
gies, specifically bipolar radiation and built-in powered subwoofers. Chris believed
these concepts would be of general interest to AVguide Monthly readers, and
asked me to write a short piece describing them (without, of course, turning the
article into a 2-page ad for my company).
"...our first product, the BP10 loudspeaker, was also a narrow
tower with basically two complete full-range driver arrays.
One faced forward and the other rearward. This is the basic
concept of a bipolar speaker. The two driver arrays radiate
sound (in phase with one another) in what is basically an
omnidirectional pattern, exactly as sound is radiated in real life
from an original sonic event."
in Home Theater, Stereo, Film and Music
Bipolar
SC
Issue 3 April 2004
I have always liked speakers with unconventional radiation
(i.e., non-forward-radiating) patterns. The first true audiophile
loudspeaker I owned was the KLH 9 full-range electrostatic. This
was in 1972. These speakers had a "you are there" imaging
presence and boxless sound quality I had never heard before.
There were many reasons for this, but an important key to their
performance was the fact that they radiated sound both for-
ward and rearward.
To me, imaging is the real magic in a loudspeaker's performance.
All the conventional parameters of a loudspeaker's performance
(linear wide frequency response, low distortion, excellent transient
response, etc.) are important, but imaging is that elusive quality
that brings the musicians into the room or brings you into the
concert hall or into the movie. Imaging allows the suspension of
disbelief and lets you imagine that what you are listening to is
real. The KLH electrostats were wonderful in this regard.
Full-range electrostatic panels of that day, including the
KLH, however, had many shortcomings, including very high price,
large size, difficult power requirements (I used a set of Futterman
output transformer-less vacuum tube amplifiers, which did a bet-
ter job than most with problematic electrostatic speaker loads),
limited dynamic range, limited bass performance, positioning dif-
ficulties, etc. It seemed to me that it would be fantastic to create
a loudspeaker that brought the benefits of these exotic, impracti-
cal panels into a product that made sense for the majority of
listeners in the real world.
I designed my first bipolar loud-
speaker in 1973 or 1974, a narrow-
format tower incorporating multi-
ple small-diameter bass/midrange
drivers arrayed on both the front
and rear baffles along
piezoelectric tweeters and passive
radiators. It was quite successful in
the marketplace. It also brought me
a phone call from the great loud-
speaker designer Jon Dahlquist
(who was also introducing a loud-
speaker with a piezoelectric tweet-
er—the soon-to-be-famous, time-
aligned Dahlquist DQ 10, which was
known for its "boxless" sound) and
led to a long and enjoyable friend-
ship between myself and Jon, as
well as with his partner, the
late Saul Marantz. (Marantz not
only founded the company which
still bears his name, but was the
creator of a number of classic
high end audio components; he also
recognized and helped cultivate
design talent in others—including
Jon Dahlquist and tuner-wizard
Dick Sequerra.)
with
Cross Section of the
Original BP2000
Sounding Board