Definitive Technology Subwoofers manual Sounding Board

Cross Section of the Original BP2000 Sounding Board

Affordable Excellence in Home Theater, Stereo, Film and Music

Sounding Board

Issue 3 April 2004

Definitive Technology’s Sandy Gross on Loudspeaker Design

The Case for Bipolar Loudspeakers with Built-in Subwoofers

Chris Martens recently reviewed the Definitive Technology BP7001SC Bipolar 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."

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 with 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.)