Floor Loudspeaker Reviews

I used DRA Labs' MLSSA system, a calibrated DPA 4006 microphone, and an Earthworks microphone preamplifier to measure the Sonus faber Sonetto V G2's quasi-anechoic frequency- and time-domain behavior in the farfield. I used an Earthworks QTC-40 microphone, which has a small (¼" diameter) capsule, for the nearfield responses.

The Sonus faber loudspeaker's voltage sensitivity is specified as 89dB/2.83V/m; my B-weighted estimate was 88.6dB(B), which is within experimental error of the specification. Sonus faber specifies the Sonetto V G2's nominal impedance as 4 ohms. The impedance magnitude (fig.1, solid trace), measured with Dayton Audio's DATS V2 system, remains above 4 ohms for most of the audioband, with a minimum value of 2.9 ohms between 90Hz and 100Hz. The electrical phase angle (fig.1, dotted trace) is high at low and very high frequencies, which means that the effective resistance, or EPDR (footnote 1), drops below 3 ohms between 43Hz and 46Hz, from 65Hz to 203Hz, and above 4.3kHz. The minimum EPDR values are 1.95 ohms at 34Hz, 1.26 ohms at 81Hz, and 2 ohms from 6.5kHz to 7.7kHz. The Sonetto V G2 is a very current-hungry load for amplifiers.

The Sonus faber enclosure seemed well-damped when I rapped it with my knuckles. Using a plastic-tape accelerometer, I found two low-level resonant modes at 398Hz and 504Hz on the sidewalls, which were strongest next to the midrange unit (fig.2). However, the low levels of these modes and their high Q (Quality Factor) will reduce the possibility of them having audible consequences.

The saddle centered on 40Hz in the Sonetto V G2's impedance magnitude trace suggests that this is the tuning frequency of the downward-firing port. (This is higher in frequency than I was expecting from this relatively large loudspeaker.) The port's nearfield response (fig.3, red trace) peaks at the tuning frequency, and its upper-frequency rolloff is disturbed by a high-level peak at 140Hz as well as lower-level peaks at 245Hz and 500Hz. I have encountered this behavior before with speakers with downward-firing ports. I suspected at that time that this is due to an air-space resonance between the base of the enclosure and the speaker's base plate and conjectured that as the port doesn't fire toward the listener, the resonance measures worse than it sounds. However, the frequency of the highest-level peak is very similar to that of a discontinuity in the impedance traces; there is also a discontinuity at this frequency in the summed nearfield output of the woofers (fig.3, blue trace).

The two woofers behaved identically, and their nearfield response had the expected reflex tuning notch at 40Hz. In the farfield, the woofers cross over to the midrange unit (fig.3, green trace) close to the specified 280Hz and roll off smoothly above that frequency. The midrange unit rolls in relatively slowly, and there is a peak/suckout combination at the top of its passband. This may well be due to a diaphragm/surround termination issue. The tweeter's output is even in the low treble but gently rises in the top two audio octaves.

This behavior can also be seen in the Sonetto V G2's farfield response, averaged across a 30° horizontal window centered on the tweeter axis (fig.4). The speaker's output in the upper midrange is 2–3dB higher than that in the regions on either side, which may well be perceived as added detail. This graph was taken without the grilles. The response with the grilles in place was identical below 4kHz and above 15kHz, but the output between those frequencies was 2–3dB lower in level with the grilles on. The complex sum of the woofers' and ports' nearfield responses, shown as the black trace below 300Hz in this graph, is disturbed by the peak at 140Hz in the port's output. The boost in the upper bass will be due to the nearfield measurement technique (footnote 2).

The speaker's horizontal radiation pattern, normalized to the response on the tweeter axis, which therefore appears as a straight line, is shown in fig.5. The dispersion is very well controlled through the midrange and treble, but the radiation pattern narrows in the top two octaves. This will tend to compensate for the gentle top-octave rise in response seen in figs.3 and 4. Not toeing in the speakers all the way to the listening position could therefore optimize the Sonus faber's treble balance. Fig.6 shows the Sonetto V G2's dispersion in the vertical plane, again normalized to the response on the tweeter axis. The speaker's output in the audioband doesn't change significantly above and below that axis, which is useful considering that at 39" from the floor with the speaker sitting on its spiked base, the tweeter is a couple of inches higher than what we have found to be the ear height of a listener in a typical chair.

In the time domain, the Sonus faber's step response on the tweeter axis (fig.7) indicates that the tweeter and woofers are connected in positive acoustic polarity, the midrange unit in negative polarity. The tweeter's output arrives first at the microphone followed by that of the midrange unit, with the decay and overshoot of its step smoothly blending with the start of the midrange step. In turn, the decay of that step then smoothly blends with the start of the woofers' step. This all implies an optimal crossover topology. Other than some low-level delayed energy at the top of the midrange unit's passband, the Sonetto V G2's cumulative spectral-decay, or waterfall, plot (fig.8) is clean. (Ignore the ridge of delayed energy close to 16kHz in this graph, which is due to interference from the measurement computer's video circuitry.)

Other than the peak in the port's nearfield output and that behavior at the top of the midrange unit's passband, the Sonetto V G2 offered relatively good measured performance.—John Atkinson

Footnote 2: A nearfield measurement assumes that the baffle extends to infinity in both horizontal and vertical planes, which means that the loudspeaker is firing into hemispherical space rather than a full sphere. See this discussion.