B&W Matrix 800 loudspeaker Measurements

Sidebar 2: Measurements

Normally, I ask reviewers to ship the products to Santa Fe for measurement once their listening sessions are over. In the case of B&W's immense 800, however, the Mountain—in the shape of Robert Harley, Stereophile's computerized test gear, and myself—decided it would be more convenient to visit Muhammad in his Arlington, VA hideout.

As explained earlier, Lewis's listening room is a small basement, with a solid floor and solid walls apart from that behind the speakers. This wall is of drywall construction, with a central doorway leading to a similarly sized exercise room, meaning that the loudspeakers both "see" a much larger space and are effectively positioned a third of the way along the long dimension of that space (footnote 1). Certainly, the prodigious levels of low bass that Lewis managed to produce from the 800s seem unreal for such a small room.

The listening seat is a sofa in front of the rear wall, and both this fact and the proximity of the sidewalls to the speakers led me to expect confused imaging from the 800s, with a somewhat shallow soundstage.

I was completely wrong. These speakers may be ugly as all get-out, but acoustically they're totally invisible. Yes, central imaging was a little broader than the best I have experienced (it was better with the grilles in place), which is something to lay at the feet of the too-close room boundaries. But the soundstage was wide and deep, with a sense of scale that I have only previously experienced from Infinity IRS Betas. Orchestras sounded as large as they do in real life; contrariwise, solo instruments and voices sounded as small as they should—listening to a solo clarinet recording on these behemoths was one of the most realistic reproduced-sound experiences I have encountered. Coupled with that ability, the 800s appeared to have no coloration, as well as offering a sense of dynamic ease that I have rarely heard, as LL mentioned, loud instruments failing to obscure quieter ones—again, as in real life. The upper-bass to lower-midrange transition was also seamlessly managed, which I assume to be due to the staggered woofer-boundary arrangement. The 800 is quite definitely a Class A speaker!

Enough of the subjectivity; how did they measure? Impedance, shown in fig.1, was to the 4 ohm spec, with a minimum value of 3.4 ohms in the upper bass at 118Hz. A more detailed examination of the impedance at low frequencies revealed the port tuning to be low, centered on 23Hz, with a maximum impedance value of 16 ohms at 44Hz. Using a 1/3-octave warble tone centered on 1kHz gave an approximate sensitivity of 94dB/W/m, which is very high. Checking the drive level at moderately loud listening levels in Lewis's room revealed that the Krell KSA-250 was merely cruising, average signal levels rarely rising above 1V—¼W! Given the 800's relatively high impedance value in the treble, it would seem that, provided the amplifier is capable of driving 4 ohm loads, the 800 is an easier load to drive than its physical bulk would imply.

Fig.1 B&W Matrix 800, electrical impedance (solid) and phase (dashed). (2 ohms/vertical div.)

All the acoustic measurements were performed with the grilles removed, as that was the way LL preferred to audition the speakers. The 800's impulse response 44" away on its tweeter axis is shown in fig.2, and offers a degree of ultrasonic ringing from the tweeter as well as a relatively lazy lower-frequency decay from the high-order crossover. The step response is shown in fig.3. These two graphs shows the impulse up to the 6ms mark, following which there were multiple reflections of the impulse, which are from the floor, sidewall, and ceiling of Lewis's listening room, respectively.

Fig.2 B&W Matrix 800, impulse response on tweeter axis at 44" (5ms time window, 30kHz bandwidth).

Fig.3 B&W Matrix 800, step response on tweeter axis at 44" (5ms time window, 30kHz bandwidth).

These reflections were windowed out in order to calculate the speaker's anechoic frequency response, which is shown, averaged across a 30° horizontal angle on the tweeter axis, in fig.4. (Because of this windowing, the frequency resolution of this graph is no better than 300Hz; unfortunately, the bulk of the speaker and the limited size of Lewis's room meant that this was the best that could be done.) Noticeable is a slight excess of energy in the top octave, as well as a broad suckout in the crossover region on this axis, which is some 46" from the floor, a little high for a typical listener. (Lewis sits with his ears on the upper-midrange axis, 38" from the floor.) On the left side of this graph is shown the complex sum of the individual midrange, woofer, and port responses, measured in the nearfield. The bump in the mid- and upper bass is primarily due to the nearfield measurement technique; without its alignment filter, the B&W 800 is basically flat down to 40Hz, below which it rolls off fairly slowly for a reflex design.

Fig.4 B&W Matrix 800, anechoic response on tweeter axis at 44", averaged across 30° horizontal window and corrected for microphone response, with the complex sum of the nearfield nearfield responses of the midrange units, woofers, and ports, plotted in the ratios of the square roots of their radiating areas below 300Hz.

Laterally, the 800 shows good, even dispersion up to 15° off-axis, though some brightness appears at 15° or more off-axis on the "pointed side." In conjunction with the proximity of LL's sidewalls to the speakers, this probably explains why he preferred the 800s with the points pointing in rather than out. Fig.5 shows how the 800's response varies with different microphone height: the rearmost curve, taken 15° above the tweeter axis, shows the crossover suckout accentuated, implying that the speaker shouldn't be auditioned by a standing listener, who will hear a rather uninvolving balance. The next-to-front and front two curves are taken on the upper- and lower-midrange axes, respectively, showing that the presence region does fill in a little, but not completely, for a listener sitting below the tweeter axis. Frankly, I was puzzled by this, as the speaker didn't sound polite, or recessed, or any other subjective adjective that could be placed at the feet of a lack of energy in this region. The mild top-octave boost only manifested itself in the form of a slight exaggeration of tape hiss and digital quantizing artifacts. Musically, it seemed irrelevant.

Fig.5 B&W Matrix 800, vertical response family at 44", normalized to response on tweeter axis, from back to front: differences in response 15° above axis, reference response, differences in response 5–10° below axis.

Fig.6 is a composite of five different measurements, showing the individual responses of one of the ports, one of the woofers, the midrange units, and the tweeter, with levels approximately matched. (The first two curves and that of the midrange below 600Hz were taken in the nearfield, with the microphone almost touching the drive-units' dust-caps; the tweeter response and the midrange response above 600Hz were taken on the HF axis at a 44" distance. The bass-alignment filter was not used for these measurements.) Moving from low frequencies to high, the port output can be seen to cover the low bass, with the notch in the woofer's output confirming the port tuning at 23Hz. Even without the alignment filter, the 800 should give good low-bass output to 30Hz or so. The crossover from the woofers to the midrange units can be seen to lie around 300Hz, with the midrange/tweeter crossover around 3kHz. The drive-units appear to be well-behaved out-of-band, the notch and subsequent peak in the woofer's response between 400 and 600Hz possibly being an interference effect due to the nearfield measurement technique. The notch in the tweeter response at 20kHz is also an interference effect, possibly from the complicated semicircular-profile "doughnut" surrounding the tweeter on the baffle.

Fig.6 B&W Matrix 800, acoustic crossover on tweeter axis at 44", corrected for microphone response, with the nearfield responses of the midrange units, woofers, and ports, plotted in the ratios of the square roots of their radiating areas.

Fig.7 shows the cumulative spectral-decay, or "waterfall," plot for the B&W 800, taken on the tweeter axis at a 44" distance. The crossover suckout can be seen to be associated with a mild degree of resonant behavior above it (shown by the cursor position just above it at 4.26kHz), while a second, still mild, resonant ridge can be seen an octave higher around 8kHz, this perhaps due to the absence of the diffraction-control grille. Apart from these slight aberrations, the plot is quite clean. Examining the speaker's various enclosure walls with a stethoscope revealed a very "dead" construction, with almost no energy emitted from any surface other than the drive-units—which is how it should be! This lack of spuriae, coupled with the speaker's high sensitivity, undoubtedly contribute to its sense of subjective ease.

Fig.7 B&W Matrix 800, cumulative spectral-decay plot on tweeter axis at 44" (0.15ms risetime).

Finally, as shown in fig.8, the bass-alignment filter offers only a moderate degree of LF boost, reaching a maximum of 5.5dB at 24.5Hz, with a steep filtering action below 20Hz. Omitting the filter to get the maximum midrange transparency of which the 800 is capable will suppress the speaker's low bass by only a small amount—but not necessarily always an unimportant amount.

Fig.8 B&W Matrix 800, response of alignment filter (5dB/vertical div.).

All things considered, this basic set of measurements shows the 800 to be a well-engineered, low-coloration, full-range loudspeaker design. What they do not reveal is the astonishing transparency that Robert Harley and I experienced in Lewis Lipnick's listening room. The only real-world loudspeakers that I think compare with the 800 are the Apogee Diva, Infinity IRS Beta, Thiel CS5, Wilson WATT/Puppy, and possibly the Avalon Ascent and Duntech Sovereign, which makes the $15,000/pair price tag seem a little more reasonable.—John Atkinson



Footnote 1: The first time I visited J. Gordon Holt's old Santa Fe listening room, in early '86, the venerable JGH had a pair of MartinLogan Monoliths set up in this exact fashion—seat against the wall, speakers a third of the way along the room's long dimension, listener therefore positioned close to the speakers—and I was impressed then with the sound produced. The speakers have plenty of room to "breathe," but the listener sits in the vividly imaging nearfield.—John Atkinson
COMPANY INFO
B&W Group North America
54 North Concord Street
North Reading, MA 01864-2699
(978) 664-2870
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