Sonus Faber Guarneri memento loudspeaker Measurements

Sidebar 3: Measurements

The Sonus Faber Guarneri memento's voltage sensitivity was a little below average, at an estimated 86dB(B)/2.83V/m. However, its plot of impedance magnitude and electrical phase against frequency (fig.1) indicates that it is not too demanding an amplifier load, though a minimum value of 4.35 ohms at 197Hz and a combination of 5.7 ohms and –38° phase at 124Hz suggest that tube amplifiers be used from their 4 ohm taps.

Fig.1 Sonus Faber Guarneri memento, electrical impedance (solid) and phase (dashed). (2 ohms/vertical div.)

Though difficult to see at the scale this graph is printed in the magazine, the very slight discontinuities in the traces just below 500Hz and just above 1kHz suggest the presence of some kind of resonant problem at these frequencies. I did find a mild panel resonance at 490Hz on the speaker's curved sides (fig.2); this is high enough in frequency and low enough in level that it should have no audible consequences.

Fig.2 Sonus Faber Guarneri memento, cumulative spectral-decay plot calculated from the output of an accelerometer fastened to the center of the cabinet's side panel (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz).

Turning to the Guarneri's acoustic behavior, the port's nearfield response (fig.3, red trace) does show a sharp peak just above 1kHz. This was faintly audible with pink noise, but the fact that the port faces away from the listener will mitigate the problem. The woofer's minimum-motion notch, where the back pressure from the reflex-port resonance holds the cone still, occurs at 46Hz (fig.3, blue trace)—the frequency of the "saddle" between the twin peaks in the impedance-magnitude trace—but the port's output actually peaks a little lower in frequency. The upper-bass boost in the summed output of the port and woofer (fig.3, black trace), which results from the nearfield-measurement protocol, is relatively mild, suggesting that the Sonus Faber actually offers an anechoically flat response in the bass, with a –6dB point around 40Hz.

Fig.3 Sonus Faber Guarneri memento, anechoic response on tweeter axis at 50" without grille, averaged across 30° horizontal window and corrected for microphone response, with the nearfield responses of the port and woofer plotted below 900Hz and 300Hz, respectively, and the complex sum of the nearfield responses plotted below 300Hz.

Higher in frequency in fig.3, the upper midrange is balanced a little forward compared with the regions above and below it, with a slight discontinuity apparent around 1.2kHz. This doesn't quite coincide with the frequency of the port resonance, so it may well be unrelated to it. The mid-treble is a little recessed, but not to the extent Keith Howard found in his measurements accompanying the review of this speaker in the March 2007 issue of British magazine Hi-Fi News (p.42). Overall, the Guarneri memento's top-octave response is smooth and extended. Fig.3 was taken with the grille removed; adding the grille produced the expected comb-filtering in the treble (fig.4), though this was modest in extent and will probably not be audible.

Fig.4 Sonus Faber Guarneri memento, effect of grille on HF-axis response (5dB/vertical div.).

The Sonus Faber's lateral dispersion was wide and even up to 8kHz (fig.5), something that generally correlates with stable, accurate stereo imaging. But the ring-radiator tweeter's output falls quite rapidly to the side in the top audio octave and above, which will give a rather mellow balance in large rooms (though of course a small speaker such as the Guarneri is unlikely to be used in such a room). In the vertical plane (fig.6), a large crossover suckout develops above the tweeter axis, as Michael mentions. Sit below the tweeter, however—as most listeners will when the Guarneri is used on its dedicated stand, which places the tweeter 43.5" from the floor and tilts the speaker back a little—and the lack of energy in the mid-treble fills in.

Fig.5 Sonus Faber Guarneri memento, lateral response family at 50", normalized to response on tweeter axis, from back to front: differences in response 90–5° off axis, reference response, differences in response 5–90° off axis.

Fig.6 Sonus Faber Guarneri memento, vertical response family at 50", normalized to response on tweeter axis, from back to front: differences in response 45–5° above axis, reference response, differences in response 5–45° below axis.

In Michael's room, the spatially averaged response taken in a grid centered on the position of the listener's head (fig.7) does indeed demonstrate superbly smooth behavior in the midrange and treble—no wonder he liked the Sonus Faber's sonic signature. However, even with the minimization of the effects of room modes provided by the spatial averaging, the fairly close placement to the room boundaries of the speakers in his room results in a boost between 40 and 70Hz and a lack of energy in the two octaves above that region. Certainly, while I was measuring the speaker in Mikey's room, I thought the midbass region sounded a little "ripe," though not unpleasantly so.

Fig.7 Sonus Faber Guarneri memento, spatially averaged, 1/6-octave response in MF's listening room.

Turning to the time domain, the Guarneri's step response on the tweeter axis (fig.8) reveals that the tweeter is connected in inverted acoustic polarity, the woofer in positive polarity. The tweeter's step smoothly hands over to the woofer's, but the slight discontinuity just before the 4ms mark ties in with the vertical dispersion graph's suggestion that the best frequency-domain integration between the two drive-unit outputs occurs below the tweeter axis. Finally, other than a slight amount of delayed energy at the frequency of the response anomaly in the upper midrange, the Guarneri's cumulative spectral-decay plot (fig.9) is superbly clean. As a result, this speaker should offer a grain-free, transparent treble.

Fig.8 Sonus Faber Guarneri memento, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth).

Fig.9 Sonus Faber Guarneri memento, cumulative spectral-decay plot at 50" (0.15ms risetime).

In common with other recent-generation Sonus Faber speakers, such as the Amati anniversario, which I reviewed in May 2006, the Guarneri memento offers excellent measured performance.—John Atkinson

Sonus Faber
US distributor: Sumiko Audio
2431 Fifth Street
Berkeley, CA 94710
(510) 843-4500