Snell XA90ps loudspeaker Measurements part 2
Fig.4 Snell XA90ps, anechoic response on tweeter axis at 50", averaged across 30 degrees horizontal window and corrected for microphone response, with the complex sum of the nearfield midrange, woofer, and port responses plotted below 300Hz.
The Snell's lateral dispersion, referenced and normalized to the tweeter-axis response, is shown in fig.5. It is superbly well controlled across the entire range; all other things being equal, this will endow the speaker with accurate, stable stereo imaging, particularly in light of the superb pair matching. In the vertical plane (fig.6), the dispersion was astonishingly wide, proving the efficacy of David Smith's "Expanding Array" concept. The Snell's balance hardly changes over a ±15 degrees window centered on the tweeter axis.
Fig.5 Snell XA90ps, lateral response family at 50", normalized to response on tweeter axis, from back to front: differences in response 90 degrees-5 degrees off-axis, reference response, differences in response 5 degrees-90 degrees off-axis.
Fig.6 Snell XA90ps, vertical response family at 50", from back to front: differences in response 20 degrees-5 degrees above HF axis, reference response, differences in response 5 degrees-10 degrees below HF axis.
In the time domain, individual inspection of the drive-unit step responses indicates that the tweeter and lower-midrange units are connected in positive acoustic polarity, the upper-midrange units and powered woofers in inverted acoustic polarity. This can be seen in the XA90ps' overall step response (fig.7), in which each drive-unit smoothly hands over to the next lower in frequency range. The Snell's waterfall plot (fig.8) is extremely clean throughout the middle and high trebles, but a resonant mode noticeable just below 3kHz might add too much of a bite on some kinds of music, while increasing the speaker's sense of transparency to recorded detail on other kinds.
Fig.7 Snell XA90ps, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth).
Fig.8 Snell XA90ps, cumulative spectral-decay plot at 50" (0.15ms risetime).
I was a little bothered by this and by the slightly shelved-down highs, which will make the Snell sound rather polite in all but small rooms. Otherwise, the XA90ps is a very respectable design, and offers superb speaker engineering for what is a very competitive price, considering its full-range nature and high dynamic range.—John Atkinson