B&W Matrix 800 loudspeaker Page 2
According to Dibb, initial one-box designs using multiple drivers, such as the preceding 808, were abandoned after listening tests proved disappointing. He mentioned that the idea of having bass units at substantially different distances from the room boundaries is not new, and "is based on the theory that the addition of two uneven responses can, with care, produce a more even result." It is for this reason that "the lower bass unit on the 800 is slightly less than one third the height of the upper, so that cancellation and reinforcement effects from the floor have very few coincident frequencies." The pentagonal shape of the bass cabinets is dictated by the need to minimize any internal standing waves produced by parallel surfaces; thus the unique shape of the woofer enclosures. While other designs were discussed, the B&W engineers finally opted for the angular shaping of the bass cabinets for reasons of structural strength and ease of manufacturing.
In the upper-frequency domain, Dibb suggested that the best results are "generally obtained when the edge of the baffle is close to the drive-unit, and when the unit dimensions are large in comparison to those of the baffle." Of course, it would be best to have the tweeter mounted on a very small baffle, such as is the case with the 801. But since the tweeter had to be in close proximity to the midrange drivers, between the two woofers, this was not possible, and the width of the midrange/tweeter cabinet became critical. Calculations apparently dictated that a baffle with the width of 7.5" (190mm) would be the best compromise, and effectively keep the first reflective high-frequency effects out of the passband of the driver.
Despite several attempts at new midrange driver designs, the existing Kevlar-coned unit used in the 801 was ultimately chosen for the 800. Since output levels required in the 800 system, particularly in the 400Hz1kHz band, would have pushed one driver to the limit, two identical drivers in parallel were incorporated. Although B&W did try a symmetrical "D'Appolito" topology with a central tweeter flanked by upper- and lower-midrange units, imaging was felt to suffer, and the final configuration with tweeter atop two adjacent midranges was chosen. While both midrange drivers give an equal output at their lowest operating frequency (380Hz), the lower of the two is attenuated at the top of its range, the upper being boosted by the same amount to give a flat response curve. This was done in order to achieve the best polar response, and prevent frequency-dependent imaging and phase problems between tweeter and lower-midrange unit.
The cones of the two 12" bass drivers are made from the same Cobex material used in the 801's unit. Soon after the introduction of the 800 speaker, a rubber woofer surround was introduced. Dibb mentioned that their work on the 803, 804, and 805 speakers, subsequent to the initial development of the 800, indicated that the "speed" of the bass attack is dependent on the amount of mechanical damping in the driver (mainly the surround). If the ratio of this to the electromagnetic damping of the driver is reduced, the relative speed of the bass and midrange is improved.
The 1.25" metal-dome tweeter was apparently conceived as a high-efficiency, high-power unit for professional pop music use. This driver is capable of producing 93dB/W continuous (actually 96dB, but it's padded down 3dB to maintain lower coil temperatures), with a maximum compression on attack of only 0.5dB. Dibb suggests that this accounts for the excellent transient response of the 800 speaker system. Ferrofluid cooling is incorporated in this new tweeter design, as it is in all of B&W's new 800 series speakers (including, now, the 801). The large diameter of this new driver means an increased directionality of high frequencies (relative to smaller tweeters), so B&W has incorporated both phase and "loading" rings around the tweeter that minimize high-frequency beaming, giving the unit a more constant directionality over its entire passband. According to the manufacturer, this tweeter is capable of producing 120dB+ dynamic peaks at 4m in a normal listening room.
As the power handling of the 800 is effectively double that of the 801, the APOC (protection circuitry) incorporated in the 801 was deleted from the 800. Dibb felt that past experience with the 801 suggested that APOC is largely superfluous, and that most domestic users will probably never see the protection system operate. He pointed out that the people at B&W were becoming more and more aware of the deleterious sonic effects of various obstacles in the signal path, and that it would not be worth risking any possible audible effects of relays or other such devices for the "sake of one lunatic who might pump enough power in to damage the speakers." (We all know that no Stereophile reader would think of doing such a thing!)
The 4 ohm input impedance characteristic was chosen for two principal reasons. First, the B&W engineers felt that most good amplifiers (with which this system will, no doubt, be used) would deliver their maximum power into 4 ohms or less. The second refers to the ideal situation where the driving amplifier runs out of volts and current at the same time, thereby delivering the maximum power to the speaker load. This, according to Dibb, is more likely to occur with a 4 ohm load.
If you're the type of person who loves to tinker with your car every weekend, and don't mind having to remove half of the engine in order to change the plugs, you'll love deciphering the 800 owner's manual and assembling these monsters. But if you're like me, this could be a big pain. The 800 comes in six large crates, with no indication of which to unpack first or where anything is supposed to go. The manual is confusing, and often incorrect, which may make you question your ability to read English ("this screw just doesn't fit into that hole!"). Luckily, in my case, Victor Goldstein (consultant to B&W), Chris Browder (Executive Vice President of B&W Loudspeakers of America), as well as two members of our musicians' listening group (Al Merz, Ed Kelly) came to the rescue. Victor had set up several pairs of 800s before these, and knew pretty much what to do, while the rest of us looked on in utter disbelief. I recommend that at least two people be available when you assemble your 800s (lifting the midrange/tweeter and upper woofer modules into place requires a combination of brute strength and finesse); better yet, let your dealer do all the work. It took five of us the better part of a day (nine hours) to unpack, assemble, and position my review pair.
My first exposure to the Matrix 800 speaker was somewhat of a shock...a very negative shock. It was at the 1990 Stereophile High End Show in New York, where the US debut of this mysterious new super-speaker took place. I had already read a review of the 800 in the German publication Audio, which had proclaimed it to be the best of the best. So, naturally, I was hoping for something that would blow me over. It blew me over, all right, but in the wrong direction. Tubby, overbearing midbass, detached and opaque midrange (or lack of same), and recessed high frequencies greeted my ears. A major disappointment. The two speakers were set up in a large, heavily acoustically damped exhibit room, and they sounded terrible. By the third day of the show, much of the room treatment had been removed, with significant sonic improvement. Much better, but still no cigar.
It wasn't until I heard the same speaker in Brussels, Belgium, during a National Symphony European tour, that I began to realize that this was a truly great product, and that the New York experience had been an aberration. Since that time, I have auditioned 800s in several venues around the world, and have come to the conclusion that this speaker is ruthlessly revealing of everything upstream, be it electronics or source material (footnote 2).
The 800s work surprisingly well in my small listening room (15' 4" W by 16' 3" L by 6' 10" H), in spite of the low ceiling which allows about 4" of clearance above the top of the speakers (footnote 3). Although B&W conditionally recommends that the speakers be placed well out from the rear wall, angled in toward the listener (to prevent shifting of the image with head movements), with woofer points outward (away from the opposing speaker), my experience, so far, would suggest that there is no set rule; experimentation is of utmost importance. I have the two speakers set approximately 3½' from the rear wall (which is lined by cabinets full of LPs and CDs), with woofer points facing inward, placing the central midrange/tweeter cabinets 6½' apart, on center. Each speaker is about 2½' from the side wall. The two speakers are angled inward, slightly more open than total convergence at listening position, which is 9½' from the drivers.
Although several other configurations were tried, this appeared to create the best balance of soundstage dimensionality, along with the fewest room/speaker interface problems. I have found, both in my listening room and at the listening room at B&W's Steyning research facility, that placing the woofer points outward causes some ringing that may be due to reflections from the midrange drivers along the concave cavity between woofer enclosures from the room side walls. There is a slightly wider soundstage with the points out, but an upper-midrange emphasis in this position makes everything sound a bit forward and hard in my room.
Quad-wiring appears to improve all areas of performance (soundstage dimensionality, transparency, and extended response at both frequency extremes, footnote 4). Quad-wiring is easy: simply run four speaker cables per channel from the amplifier to each of the four pairs of binding posts (two woofers, midrange, and tweeter) of each speaker. Of course, so much high-quality speaker cable can do significant damage to the bank account, but the sonic improvement is well worth the bucks. Tri-wiring (separate cables to midrange and tweeter, and single cable to lower woofer with jumper to top woofer) does not work nearly as well. In this configuration, the upper midrange is too prominent, causing the speaker to sound unnaturally forward. I have not yet tried to bi-amp the 800s. Past experience has shown that identical amplifiers are necessary for correct top-to-bottom balance on any good speaker, and I don't yet have a pair of identical amplifiers. Furthermore, this speaker will probably be used more often with a single amplifier, so this review will reflect that situation.
Footnote 2: I found out, after the fact, that the New York B&W 800 exhibit used out-of-the-box Jeff Rowland electronics and Straight Wire speaker/interconnect cables, all of which, in my experience, sound absolutely dreadful until after several hours of burn-in. I've also discovered that this speaker does not need, or like, highly acoustically damped rooms. Best results are obtained in average listening rooms with little or no sonic treatment.
Footnote 3: In point of fact, however, the room is effectively larger than meets the eye, since an open door between the two speakers into a second, smaller room affords a larger bass-loading area. There is also an open staircase up to the main floor on one side of the listening room, further extending the bass-loading area throughout the entire first floor.
Footnote 4: Bass performance is particularly improved with separate wiring to each woofer. Several people who are technically more knowledgeable than I have suggested that this is probably due to a decrease in the effective output impedance of the amplifier.