B&W Matrix 801 Series 2 loudspeaker Measurements

Sidebar 2: Measurements

Stereophile's analysis of the B&W Matrix 801 was published long before the magazine acquired the DRA Labs and Audio Precision measurement systems used for its loudspeaker reviews. As my wife owns a pair of the big B&Ws, however, I have measured the speaker at various times over the past 13 years. Here, then, is a complete but never-before-published set of measurements to accompany Lewis Lipnick's 1987 review.

At an estimated 87dB(B)/W/m sensitivity, the B&W 801 is average in this respect. But as can be seen from the plots of its impedance magnitude and phase (fig.1), it is a fairly easy load for the partnering amplifier to drive. The magnitude hardly drops below 6 ohms, and while the maximum electrical phase angle (53.6 degrees capacitive at 2.8kHz) is fairly extreme, the impedance at this frequency is very high at 15.3 ohms, which will mitigate any negative effects.

Fig.1 B&W Matrix 801, electrical impedance (solid) and phase (dashed). (2 ohms/vertical div.)

The saddle at 19Hz in the magnitude trace indicates the tuning frequency of the big flared port—very low! That this graph is free from any glitches that would indicate the presence of enclosure resonances was confirmed using a simple plastic-tape accelerometer to assess the panels' vibrational behavior. Waterfall plots calculated from the accelerometer output when it was attached to the sides of the fibercrete "head" unit (fig.2) and the Matrix bass bin (fig.3) showed that both were almost completely free from the ridges of delayed energy that would imply the presence of panel resonant modes.

Fig.2 B&W Matrix 801, cumulative spectral-decay plot of accelerometer output fastened to side of midrange "head." (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz.)

Fig.3 B&W Matrix 801, cumulative spectral-decay plot of accelerometer output fastened to side panel of bass bin, 12" from base. (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz.)

Fig.4 shows that without the electronic equalizer, the port output, which covers the 15-50Hz region, is somewhat suppressed compared with the woofer's output. But this fundamentally overdamped alignment endows the 801 with the maximum flexibility when it comes to optimizing the speaker's interaction with the room. If you have a small room—or must use the speakers fairly close to the wall behind them, as my wife does—then you can dispense with the equalizer and still get extended bass performance, owing to the boundary reinforcement at low frequencies. In a large room that doesn't offer the same degree of low-frequency "room gain," the equalizer will bring up the low bass, the 801's damped reflex alignment minimizing any propensity for overhang that would otherwise muddy the sound. And as LL found, the presence of extended and powerful low frequencies then better balances the somewhat forward mid-treble region.

Fig.4 B&W Matrix 801, anechoic response on tweeter axis at 50", averaged across 30 degrees horizontal window and corrected for microphone response, with the nearfield woofer and port responses plotted below 1kHz and 600Hz, respectively.

Higher in frequency, the response trend (averaged across a 30 degrees lateral window on the tweeter axis) is basically flat, but with a slight excess of energy in the presence region and a corresponding lack of energy in the top octave. All things being equal, this will make the speaker both a little too revealing of recorded detail and somewhat fussy when it comes to the quality of source and amplification components, just as LL noted in his auditioning comments.

A speaker's perceived in-room balance will depend not only on its on-axis response but also on how that response changes to the speaker's sides. Figs.5 and 6 show the Matrix 801's lateral dispersion on the tweeter axis. (Fig.5 shows the actual responses; fig.6 shows just the differences between the off-axis responses and the tweeter-axis response.) The 801's midrange unit starts to get directional at the top of its passband—indicated by the cursor in both graphs—but the tweeter, with its baffleless mounting, has very wide dispersion at the bottom of its passband. The result is a slight degree of "flare" in the same region where the on-axis response has an excess of energy, which in all but very large rooms will accentuate the "revealing" nature of the speaker.

Fig.5 B&W Matrix 801, lateral response family at 50", from back to front: responses 90 degrees-5 degrees off-axis, reference response on tweeter axis, responses 5 degrees-90 degrees off-axis.

Fig.6 B&W Matrix 801, lateral response family at 50", from back to front: differences in response 90 degrees-5 degrees off-axis, reference response on tweeter axis, differences in response 5 degrees-90 degrees off-axis.

54 Concord St.
North Reading, MA 01864-2699
(978) 664-2870

Jason P Jackson's picture

The 801s2 is the device which at once, upon first listen, made me understand what
a."holographic imaging" and "soundstage" was
b. why we have 2 channels
c. why they call this thing "High Fidelity".