Usher Audio Technology Compass X-719 loudspeaker Measurements

Sidebar 3: Measurements

The Ushers arrived at my home rather the worse for wear, their single packing box and internal Styrofoam inserts not being up to the task of protecting the speakers from the ravages of UPS. A speaker this hefty needs to be individually packed, in my experience. Fortunately, most of the damage was cosmetic, and while the crossover's large air-cored inductor was hanging by its connecting leads in the less damaged of the pair (S/N B012830), the speaker did function correctly. All the measurements were therefore performed on this sample, with its grille off (the grille fittings had been snapped off in shipping).

The Compass X-719 is of average voltage sensitivity, at an estimated 87.5dB(B)/2.83V/m, which is within experimental error of the specified 88dB. Its impedance (fig.1) lies above 8 ohms throughout almost the entire bass and midrange, though it does drop to an average of 6 ohms in the treble. The speaker's high frequencies will definitely sound less lively with a tube amplifier having a high source impedance, as a result of the overall difference between the midrange and treble impedances. I would have classified the Usher as being very easy for an amplifier to drive, were it not for the combination of 5.4 ohms magnitude and -43 degrees phase angle at 2.5kHz.

Fig.1 Usher Compass X-719, electrical impedance (solid) and phase (dashed). (2 ohms/vertical div.)

The slight wrinkle in the impedance traces at around 450Hz implies the existence of some kind of cabinet resonance. Examining the panels' vibrational behavior did indeed reveal a single strong mode present at 461Hz on the sidewalls (fig.2), though this might well be high enough in frequency to "fall between the cracks" with concert-pitch music. (The higher the "Q," or "Quality Factor," of a resonance, the longer it needs to be stimulated with exactly the right frequency to be fully excited.)

Fig.2 Usher Compass X-719, cumulative spectral-decay plot calculated from the output of an accelerometer fastened to the cabinet's side panel. (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz.)

The saddle at 41Hz in the impedance-magnitude trace suggests that this is the tuning frequency of the 2"-diameter port on the rear panel. This is confirmed both by the sharp notch at 41Hz in the woofer's nearfield output and the broad peak in the port's response centered on the same frequency (fig.3). Two sharp peaks, at 350Hz and 780Hz, can be seen in the port's output above its passband, suggesting the presence of resonances at these frequencies. Suspiciously, there is a small suckout in the woofer's response at 350Hz.

Fig.3 Usher Compass X-719, acoustic crossover on tweeter axis at 50", corrected for microphone response, with nearfield responses of the woofer and port plotted below 300Hz and 1kHz, respectively.

The crossover between the woofer and the tweeter lies just below the specified 2kHz, with what appears to be a third-order slope to the tweeter's high-pass filter. The woofer's rolloff is more shallow, broken by peaks at 3kHz, 8kHz, and just above 10kHz. The tweeter's output is even in the bottom part of its passband, but there is a little too much on-axis energy around 10kHz. This boost is still apparent when the X-719's farfield output is averaged across a 30 degrees horizontal window on the tweeter axis (fig.4). Together with the slight excess of energy in the two octaves below 10kHz, this will lead to the balance that Bob Reina described as "forward." I suspect the upper harmonics of instruments are being reproduced a little too hot in level, which he perceived as "forwardness" rather than as brightness per se. As I said in my discussion of the Usher's impedance, this is something that will be ameliorated if a tube amplifier is used.

Fig.4 Usher Compass X-719, 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 woofer and port responses, taking into account acoustic phase and distance from the nominal farfield point, plotted below 300Hz.

The suckout around 300Hz is apparent in this graph, but the bass is actually well-extended, even allowing for the usual boost that accompanies the nearfield measurement technique. BJR described the X-719's bass as being "buxom," but if anything, I would have thought the lows should have sounded tight as well as deep.

Fig.4 was taken on the tweeter axis, and a suckout is apparent at the top of the woofer's passband. Fig.5 shows that this suckout fills in 5-10 degrees above the tweeter axis, which suggests low stands would be more appropriate than high. BJR's 24" stands, for example, place the Usher's tweeter 39" from the floor, which might explain Bob's finding the speaker's midrange to sound a bit laid-back. On the other hand, he may have been reacting to the lack of off-axis energy in the lateral plane at the top of the woofer's passband (fig.6). Note that the tweeter gets decidedly more directional above 6kHz, which in well-damped rooms will tend to work against the excess of on-axis energy in the same region. However, this will make the low treble sound more prominent.

Fig.5 Usher Compass X-719, vertical response family at 50", normalized to response on tweeter axis, from back to front: differences in response 45 degrees-5 degrees above axis, reference response, differences in response 5 degrees-45 degrees below axis.

Fig.6 Usher Compass X-719, 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.

The X-719's step response (fig.7) indicates that both its drive-units are connected with the same, positive acoustic polarity. The waterfall plot (fig.8) shows a clean initial decay, though there is some delayed energy associated with the peaks in the woofer's out-of-band behavior.

Fig.7 Usher Compass X-719, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth).

Fig.8 Usher Compass X-719, cumulative spectral-decay plot at 50" (0.15ms risetime).

Usher's Compass X-719 offers a lot of speaker for $1000/pair: it's well-made, well-finished, has high-quality parts, and its powerful, extended low frequencies are unusual in this price region. Still, its measured performance does reveal some anomalies.—John Atkinson

COMPANY INFO
Usher Audio Technology
US distributor: Thee High End
6923 Inwood Rd.
Dallas, TX 75209
(214) 704-6082
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