Definitive Technology BP10B manual Stereo Review, Julian Hirsch, Hirsch-Houck Laboratories

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Stereo Review

DEFINITIVE TECHNOLOGY BP10 BIPOLAR SPEAKER SYSTEM “...a truly outstanding speaker system.”

Julian Hirsch, Hirsch-Houck Laboratories

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.

“Definitive Technology’s first product is an unusual loudspeaker that offers exceptional performance…”

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

D E F I N I T I V E TE C H N O L O G Y ’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

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

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-