B&W Signature 800 loudspeaker Measurements part 2
As I explained earlier, the Signature 800's bulk meant I couldn't use my remote-controlled speaker turntable. It wasn't possible, therefore, to take my usual complete set of lateral off-axis response measurements. However, fig.5 shows the manner in which the 800's output changes over the 30 degrees window used to derive the anechoic response in fig.4. It hardly changes at all, which is astonishing given the fairly large radiating diameter of the midrange unit and the high 4kHz crossover frequency. This suggests excellent dispersion, with equally superb, stable stereo imaging.
Fig.5 B&W Signature 800, lateral response family at 50", from back to front: differences in response 15 degrees-5 degrees off-axis, reference response on tweeter axis, differences in response 5 degrees-15 degrees off-axis.
In the vertical plane (fig.6), a significant suckout develops at 4kHz above the tweeter axis. This is a high 45" from the ground, however, and the response on the midrange axis, the second trace from the bottom in fig.6, which will be more typical of what a seated listener will hear, is not significantly different.
Fig.6 B&W Signature 800, vertical response family at 50", from back to front: differences in response 15 degrees-5 degrees above tweeter axis, reference response, differences in response 5 degrees-10 degrees below tweeter axis.
In the time domain, the step response (fig.7) indicates that all three drive-units are connected with the same positive acoustic polarity. The cumulative spectral-decay plot (fig.8, windowed a bit more aggressively than usual to eliminate the floor bounce mentioned earlier) is very clean throughout the treble, except for some delayed energy at 4kHz associated with the slight on-axis peak at that frequency.
Fig.7 B&W Signature 800, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth).
Fig.8 B&W Signature 800, cumulative spectral-decay plot at 50" (0.15ms risetime).
Measuring a large heavy speaker is, to some extent, an exercise in frustration. This is because the usual assumption made—that the measuring microphone is in the farfield—is no longer true, and because the speaker's sheer bulk makes the measurement process more laborious than usual. (My thanks to B&W's Tim Wyatt for his help in arranging the review logistics.) It's possible, therefore, that my Signature 800 measurements are affected by a wider margin of experimental error than normal. Certainly, the Proximity Effect, due to the microphone distance not being significantly greater than the largest radiating dimension, would tend to slope down the measured response.
But there's still plenty of good stuff here. I'm not surprised KR was so impressed by the B&W Signature 800's sound quality.—John Atkinson