Sony SS-AR2 loudspeaker Measurements
Sidebar 3: Measurements
I used DRA Labs' MLSSA system and a calibrated DPA 4006 microphone to measure the Sony SS-AR2's frequency response in the farfield, and an Earthworks QTC-40 for the nearfield and spatially averaged room responses.
My estimate of the SS-AR2's voltage sensitivity was slightly higher than the specified 89dB, at 90.5dB(B)/2.83V/m. However, while the impedance is specified as 4 ohms, the magnitude drops below 4 ohms for most of the lower midrange (fig.1). The minimum magnitude is 2.6 ohms at 110Hz, and there are also current-hungry combinations of 4 ohms magnitude and 47° electrical phase angle at 80Hz, and 4 ohms and +43° at 700Hz, suggesting that a good, 4 ohm-rated amplifier will work best with this speaker.
There are no wrinkles in the impedance traces that would suggest the presence of cabinet vibrational modes; investigating the enclosure's behavior with a simple plastic-tape accelerometer, I found a couple of very low-level modes around 500Hz that were present on all surfaces, but nothing else other than a low-level mode at 59Hz (fig.2).
The saddle in the impedance-magnitude trace centered on 30Hz suggests that this is the tuning frequency of the lower port, which loads the twin woofers. The blue trace in fig.3 is the sum of the nearfield responses of the woofers, and it does indeed have the expected notch at 32Hz. However, the lower port's output, measured in the nearfield (red trace), peaks a little lower in frequency and its output covers a broader passband than usual, not rolling off until above 80Hz. Commendably, its output contains no significant upper-frequency peaks. I haven't shown in fig.3 the upper port's output, which is very low in level; this port extends the midrange unit's dynamic range rather than contributing to its lower-frequency output. The green trace in fig.3 shows the nearfield response of the midrange unit. It appears to cross over to the woofers a little lower than the specified 300Hz, but this may well have been skewed by the nearfield measurement technique, which assumes a 2pi acoustic environment; ie, one that extends to infinity in the vertical and horizontal planes in front of the speaker.
Below 300Hz, the black trace in fig.3 shows the complex sum of the midrange, woofer, and port nearfield responses; above 300Hz, it shows the SS-AR2's farfield response averaged across a 30° horizontal window centered on the tweeter axis. Overall, it meets tight limits, but a shallow valley in the mid-treble is accentuated by a slight excess of energy in the top octave. The soft-dome tweeter extends at full level to the 30kHz limit of my graph. The Sony's plot of lateral dispersion (fig.4) features evenly spaced contour lines, but with a lack of off-axis energy at the top of the midrange unit's passband. In a typical room, this might add to the slight on-axis valley in the presence region to render the SS-AR2's sound a little polite. However, the dispersion in the vertical plane (fig.5) indicates that while a large suckout develops at 4.5kHz for listening axes above the tweeter, which is 36" from the floor, the presence-region valley fills in 5° and more below the tweeter axis.
To investigate the Sony's in-room balance, I performed my usual spatially averaged response measurement in my listening room. Using SMUGSoftware's FuzzMeasure 3.0 program, I average 20 spectra, taken for the left and right speakers individually, in a vertical rectangular grid 36" wide by 18" high and centered on the positions of my ears. This eliminates the room acoustics' more egregious effects on the measurement, and integrates the direct sound of the speakers with the in-room energy to give a curve that I have found correlates quite well with a speaker's perceived tonal balance.
The result is the red trace in fig.6. For reference, the blue trace shows the spatially averaged response of the Lansche 5.1 speaker, which I reviewed in July 2012. The Sony's in-room output is, overall, smooth and even. However, interpreting traces such as this is not straightforward, because which band of frequencies the ear takes as its reference will depend on the music. Though I could hear the slight peak between 1 and 2.5kHz with pink noise, with the music I listened to, I suspect that my ears took the peak as being correct, which means that the mid-treble will be a little recessed, leading to my impression of the SS-AR2 having a more polite balance than the Lansche. Lower in frequency in fig.6, the peak just below 30Hz and the dip at 45Hz are due to room effects that have not been eliminated by the spatial averaging; however, the Sony does produce a little too much lower-midrange energy in-room, which will add richness and warmth to its sound. By contrast, as reported in my review, the Lansche has a lack of energy in the same region.
In the time domain, the SS-AR2's step response on the tweeter axis (fig.7) indicates that the tweeter and midrange units are connected in inverted acoustic polarity, the woofers in positive polarity, and that the tweeter's output arrives first, followed by the midrange's and then the woofers'. However, the fact that the decay of each unit's step blends smoothly into the start of the step of the next unit lower in frequency correlates with the excellent frequency-domain integration of their outputs seen in fig.3, and implies optimal crossover design.
The Sony's cumulative spectral-decay plot on the tweeter axis (fig.8) is superbly clean overall, though there is a slight amount of delayed energy associated with the small on-axis peak in the upper midrange. (Ignore the black ridge of delayed energy just below 16kHz, which is due to leakage from the computer's video circuitry.)
Sony's SS-AR2 offers superb measured performance that correlates well with my positive impressions of its sound quality.John Atkinson