Snell Acoustics XA 2900 surround speaker system Measurements
The sensitivity of the XA 2900 Tall (L/R) measured 90dB/W/m. Its sealed cabinet is tuned to approximately 30Hz, with a minimum impedance of 2.7? at 78Hz. The impedance phase is very capacitive at approximately 40Hz, which might normally make a speaker a difficult load. But that should not be a concern here: The impedance magnitude is about 8? at that frequency, and the input to the speaker will likely be rolling off rapidly by that point in favor of the subwoofer. But the impedance does remain below 4.3? from 60Hz to 1kHz. Because of this, I would rate the nominal impedance at a conservative 4?, and the XA 2900 a moderately difficult to drive. If the XA 2900 is paired with a well-designed amplifier comfortable with low-impedance loads, however, it should encounter no difficulties.
The pseudo-anechoic response of the XA 2900 Tall at tweeter height, averaged over a 300 forward horizontal angle and combined with the nearfield response of the woofers, is shown in Fig.1 (violet). The useful bass extends down to about 26Hz (-10dB relative to the output at 1kHz). The on-axis average is very smooth, particularly through the midrange. There are a few minor ripples in the treble, but no visible peaks. The response is down a bit in the higher frequencies, starting at about 10kHz. The deviation is not serious or even unusual, but could explain the very slight lack of sparkle noted on top in the auditions. Off-axis, the response falls as expected in the upper octaves. There is a noticeable suckout just below 2kHz at extreme off-axis angles, but nothing in my listening notes indicates that this caused any audible problems.
Fig.2 again shows the XA 2900 Tall's averaged horizontal front response (violet), plus the vertical responses taken at +150 (red) and -150 (blue) relative to the tweeter axis. Again, a small and audibly inconsequential dip shows up off-axis, here at about 2.6kHz. The vertical listening position appears relatively noncritical within the ±150 limits.
The XA 2900's frequency-compensation switches have a relatively moderate effect through the bass and midrange (we measured their effect from 200Hz up), with a maximum cut of 2.4dB at 200Hz in the down position and a maximum boost of 1.4dB at 500Hz in the up position. They are more active in the treble. With both the low and upper treble switches set to the plus positions, the boost was approximately 2.4dB at 5kHz, 3.7dB between 10kHz and 15kHz, and 3.3dB at 20kHz. The maximum cut with the switches in the negative settings was about -3dB at 3kHz.
The XA 2900 Standard (center channel) is in many ways similar to the XA 2900 Tall. It has approximately the same sensitivity, and its cabinet is also tuned to 30Hz, with a minimum impedance of 2.9? at 78Hz. Its impedance characteristics are similar overall, and though its impedance magnitude is a little higher in the critical 60Hz-1kHz region, remaining below a maximum of 5.4? through this band, I would still recommend that the speaker be used only with amplifiers comfortable with low-impedance loads. The XA 2900 center's bass also extends usefully down to 26Hz (-10dB). And its frequency-tailoring switches have essentially the same effect.
The measured front horizontal response of the XA 2900 Standard, taken on the tweeter axis and averaged in the same manner as described above for the XA 2900 Tall, is shown in Fig.3 (violet). The on-axis average still remains within good tolerances (±2dB across most of the frequency range), but is neither as smooth nor as flat as the XA 2900 Tall's. There is an elevation through the midrange and low treble (30Hz-3kHz) that may account for the slight forwardness I heard from the system. The horizontal off-axis performance is also more uneven, though this caused no obvious aberrations in the listening tests.
The ±15? vertical off-axis performance of the XA 2900 center (Fig.4) is good, though the off-axis dip at 2.6kHz is deeper than in the Tall. I recommend that the vertical listening window be kept reasonably close to the tweeter axis for the best response.
Altogether, this is a good set of measurements, the main limitation being a little more roughness in the off-axis curves than we like to see—a roughness that does not, however, appear to compromise the sound of the Snell system. And since the XA 2900 Tall did produce a marginally better set of results, I recommend the use of this model across the three front channels, if your installation can accommodate it. With proper planning, this arrangement should not be difficult if the center-channel speaker is positioned behind a projection screen.—TJN