Sony SS-AR1 loudspeaker Measurements
Sidebar 3: Measurements
My estimate of the Sony SS-AR1's voltage sensitivity was both higher than specified and usefully higher than average, at just above 90dB(B)/2.83V/m. However, its plot of impedance magnitude against frequency (fig.1, solid trace) indicates that it will be drawing more than 1W from the amplifier at that 2.83V level. The impedance drops below 4 ohms for much of the midrange, reaching a minimum value of 2.7 ohms between 350 and 400Hz and at 95Hz. The electrical phase angle (fig.1, dotted trace) is also quite severe at some frequencies; the combination of 3.4 ohms magnitude and 53° phase angle at 70Hz, a frequency where music can have a significant amount of energy, will require the Sony be used with an amplifier that is not fazed by 2 ohm loads.
The traces in fig.1 are free from the small discontinuities that would suggest the presence of cabinet resonant modes. Investigating the cabinet panels' vibrational behavior with a simple plastic-tape accelerometer uncovered nothing of concern. Fig.2, for example, shows a cumulative spectral-decay plot calculated from the accelerometer's output when it was fastened to the center of the rear panel. A ridge of delayed energy can be seen at 520Hz, and this could also be detected on the side and top panels, but this was very low in level on all surfaces and will be subjectively inconsequential.
The Sony's impedance-magnitude trace has a saddle in the low frequencies between 20 and 30Hz, and the woofers' output in the nearfield (fig.3, blue trace) has the expected minimum-motion notch at 28Hz. The two woofers behave identically and roll off cleanly above 250Hz or so. The output of the lower port on the rear panel (red trace) has a broader bandpass than usual, but rolls off cleanly above 70Hz. I haven't shown in this graph the nearfield output of the midrange unit, or of the upper rear-panel port that loads it, but the crossover from the woofers to the midrange occurs around 400Hz, as specified. The upper port doesn't extend the output of the midrange unit; however, it does have a peak in its output just below 700Hz. Fortunately, the fact that the port is on the rear of the cabinet will ameliorate any coloration that might result from this behavior.
The black trace below 300Hz in fig.3 shows the complex sum of the nearfield midrange, woofer, and port responses, taking into account acoustic phase and the different distances of each radiator from a nominal farfield microphone position. The 2pi acoustic environment that is assumed by the nearfield technique does give rise to a peak in the upper bass, but that peak for the Sony is more extreme than usual. This correlates with Kal Rubinson's finding the SS-AR1 to have "remarkably full, extended bass," if on the rich side overall. Taking into account the upper-bass, measurement-related boost, the lows are down by 6dB at 32Hz, which will result in true 20Hz extension in all but very large rooms.
I measured the Sony SS-AR1's frequency response in the farfield with DRA Labs' MLSSA system and a calibrated DPA 4006 microphone. Higher in frequency, the Sony speaker is remarkably flat throughout the midrange and mid-treble, its farfield response averaged across a 30° horizontal window meeting superb ±1.5dB limits from 300Hz to 9.9kHz. The top octave is slightly elevated, but if you look at the plot of the SS-AR1's horizontal dispersion (fig.4), you can see that the tweeter does become more directional in this region. This will result in a correctly balanced top octave in rooms of small to moderate size. The dispersion is commendably wide and even throughout the midrange, but the midrange unit itself does become directional just below the crossover frequency of 4kHz, which results in a slight off-axis flare between 5 and 7kHz. It may be possible that this slight lack of low-treble energy off-axis would result in KR's initial reaction that the SS-AR1 lacked "snap and sparkle" and led to his needing to experiment with set-up. In the vertical plane (fig.5), a suckout at the upper crossover frequency develops immediately above the tweeter axis, which is 39" from the floor. Below that axis the response changes only slightly, which is optimal design for seated listeners.
In the time domain, the Sony's step response on the tweeter axis (fig.6) indicates that the tweeter and midrange are connected in inverted acoustic polarity, the woofers in positive polarity. I confirmed this by looking at the step responses of the individual drive-units (not shown); the important point to note is that the decay of each unit's step in this graph blends smoothly with the start of the unit next lower in frequency. This implies optimal crossover design and correlates with the excellent integration of the drive-units' outputs in the frequency domain. The SS-AR1's cumulative spectral-decay plot (fig.7) demonstrates superbly clean decay through the region covered by the tweeter. (Ignore the dark ridge just below 16kHz, which is the usual pickup of the computer monitor's line-scan radiation.)
The Sony SS-AR1's measured performance indicates almost textbook design, and that beautifully constructed enclosure is as acoustically effective as it is drop-dead gorgeous to look at. I am not surprised that KR considers it a "statement" product.John Atkinson