Definitive Technology Bipolar BP-8040ST 5.1-Channel Speaker System (TPV 108)

Bipolar Design Gives Huge Soundscapes

In pop psychology the term “bipolar” describes a personality disorder, but in loudspeakers it references a design format known to yield giant, spacious soundstages—one of the very qualities we like most about Definitive’s Bipolar BP-8040ST surround system ($2595). Bipolar loudspeakers, as many of you know, feature both forward and rearward-firing driver arrays—an arrangement that offers several benefits, among them more even power response throughout the room, plus a tendency for that rear wave of acoustic energy to reflect off the wall behind the speakers creating a convincing illusion of expanded soundstage width and depth.

Bipolar speakers are as much a part of Definitive Technology’s corporate identity as, well, the word “Definitive,” since the very first speakers that put the company on the map were bipolar models and there have been bipolar models in the lineup ever since. Thus, whenever Definitive chooses to update its bipolar range—as happened just about a year ago—it takes great care to get the designs right, since in a very real sense they tend to be the standard bearers against which the entire company may be judged. Definitive’s newest bipolar lineup centers on four floorstanding models, starting with the diminutive BP-8020ST and ranging on up to the mighty BP-8080ST. In a recent conversation with Definitive’s Senior VP of Marketing and Product Development Paul DiComo, I learned that he commends the one-up-from-the-bottom-of-the-line BP-8040ST as offering exceptionally good bang for the bucks within a product line already known for value. Indeed, DiComo has lived quite happily with a set of BP-804ST’s in his home system, even though he could bring home pretty much any Definitive model he wants.

I explained to DiComo that The Perfect Vision was interested in reviewing either a maximum performance bipolar surround system, or one that in his estimation offered maximum performance per dollar, and without hesitation he suggested the BP-8040ST based system reviewed here. The system consists of a pair of BP-8040ST floorstanders ($1598/pair), a CS-8040HD center channel speaker ($499), and a pair of SR-8040BP surround/FX speakers ($498/pair). No separate subwoofers are needed as each of the BP-8040ST’s contains a built-in, 300-watt powered subwoofer.

Before we jump into the review proper, though, let me summarize some of the technologies used in the BP-8040ST and other Definitive bipolar systems. The main speakers feature both front and rear-firing driver arrays, but unlike earlier Definitive bipolar models, those arrays are now deliberately asymmetrical, meaning that they use similar but not identical arrays on the front and back. Why the asymmetry? Definitive research suggested that it would be a good idea to have more output radiated from the front of the speaker than the back, partly because this arrangement was thought to give the best combination of imaging precision and focus, while still preserving the broad, deep soundstages for which bipolar technology is known.

Next, the BP-8040ST provides a built-in powered subwoofer with user adjustable output level controls—a feature it shares in common with other BP-ST models (where “ST” denotes Super Towers, which by Definitive tradition feature onboard powered subs). In practical terms, this arrangement means that surround systems based on BP-ST models will automatically have not one but two powered subs for more powerful and even distribution of low bass throughout the room.

Finally, all BP-ST models features unexpectedly slender tower-type cabinets, cabinets that in the case of the BP-8040ST offer footprints that takes up less than a square foot of floors area. When most people hear the word “floorstander” they imagine speakers that will be big and bulky, but that isn’t the case at all with the BP-8040ST’s, which seem very slim and compact.

But enough of background information; let’s look at how the BP-8040ST system is made and sounds.

FEATURES

BP-8040ST floorstanding speaker system, technical highlights:

• Front-firing driver array: one 1-inch aluminum dome tweeter and two 3.5-inch BDSS mid/bass drivers.
• Rear-firing driver array: one 1-inch aluminum dome tweeter and one 3.5-inch BDSS mid/bass driver.
• The aluminum tweeter is the same design that debuted in Definitive’s Mythos ST and STS models, a design that offers noticeably smoother treble response than Definitive’s earlier aluminum dome drivers did.
• The BDSS midrange driver is new-generation version of the BDSS driver that first appeared in Definitive’s ProCinema and Mythos-series speakers some years ago. The BDSS driver design features a cone-shaped driver diaphragm with a hole in the center and which is supported both by inner and outer surround rings (the inner surround ring anchored to a centrally positioned, fixed pole-piece that doubles as a waveguide). The BDSS design was originally developed with an eye toward improved power handling, but turned out to have other key benefits in terms of a significantly more responsive and open sound than many midrange drivers can produce. New in this second-generation BDSS driver is a large flared, golf tee-shaped central pole piece that is said to dramatically enhance midrange dispersion.
• Woofer driver array: one 8-inch powered woofer and two 8-inch passive radiators, driven by a built-in 300-watt amplifier.
• The woofer amp provides a built-in active crossover and a user-adjustable level control, plus a separate LFE input for those who may wish to drive the subwoofer from the LFE outputs of their A/V receivers or controllers.
• In practical terms, the active woofer system makes the BP-8040ST extremely easy to drive, since the user’s main amplifier never really drives the woofer array in the usual sense of the word. Instead, the user’s amp simply provides what amounts to an input signal so that Definitive’s onboard amp can take over the bass workload from there.
• The BP-8040ST, like all BP-series models, features a slender, black fabric-wrapped enclosure with a gloss-black endcap on the top, and a gloss-black floorplate and trim panel at the bottom. To improve stability (and thus tip-over resistance), Definitive also provides a set of four slim, bolt-on stabilizer feet that can be fitted with included floor spikes.