Chario Academy One loudspeaker Measurements
I found the Chario Academy One to be a little more sensitive than specified, at an estimated 85.5dB/2.83V/m (B-weighted). Its impedance, which remains above 10 ohms over the entire band except for regions in the lower midrange and bass (fig.1), suggests that it is a very easy load for an amplifier to drive. I'm not sure, therefore, why Larry Greenhill found it to work best with high-powered amplifiers.
Fig.1 Chario Academy One, electrical impedance (solid) and phase (dashed) (2 ohms/vertical div.).
The magnitude plot in fig.1 suggests that the rear-facing port is tuned to 50Hz, implying reasonably good bass extension for a small speaker. The impedance traces are also smooth, implying a freedom from cabinet-resonanceinduced colorations. This was confirmed by calculating waterfall plots (not shown) from the output of a plastic-tape accelerometer fastened to the cabinet surfaces. A mode was present just below 500Hz, but this was very low in level.
I used the DRA Labs MLSSA system with a calibrated B&K microphone to look at the individual responses of the drive-units and the port (fig.2); as expected, the latter is tuned to 50Hz, with a well-defined bandpass characteristic. There is a peak in its output at 750Hz, but as the port fires behind the speaker, this should not have much of a subjective effect. The woofer is flat within its passband, with a second-order rolloff above 2kHz rather than the fourth-order specified, and little evidence of cone breakup modes. The tweeter rolls in above 2kHz, again with a second-order slope, with a 5dB energy excess on-axis.
Fig.2 Chario Academy One acoustic crossover on tweeter axis at 50", corrected for microphone response, with the nearfield woofer and port responses plotted below 300Hz and 1kHz, respectively.
Fig.3 shows how these individual drive-unit responses add on the tweeter axis at a distance of 50". Interestingly, the 1992 sample that LG auditioned measured very similarly. The bass rolls off sharply below the port tuning frequency, implying a tuning of rather highish Q, which is presumably why the upper bass sounded rich to LG. The midrange and low treble seem pretty flat, though the mid-treble is a touch recessed on-axis, the top octave a little prominent. The latter seems to contradict LG's finding that the speaker sounded dark, though the slight lack of mid-treble energy might make the speaker laid-back. However, the Chario is no worse in this respect than the ProAc Response One SC that Wes Phillips reviews elsewhere in this issue. Obviously, something else is going on with the Italian speaker.
Fig.3 Chario Academy One, anechoic response on tweeter axis at 50", averaged across 30° horizontal window and corrected for microphone response, with complex sum of the nearfield woofer and port responses plotted below 300Hz.
A speaker's perceived balance depends not just on the on-axis response (which characterizes the first-arrival sound), but also on its off-axis behavior. The Academy One's lateral dispersion is shown in fig.4. (Only the differences in response compared with the on-axis response are shown, which means that the latter appears to be a straight line.) The off-axis behavior is remarkably well controlled, proving that the drive-units and sculpted baffle are working together to optimize dispersion. And the slight flare in the mid-treble (shown by the cursor position) will compensate nicely for the lack of energy in the same region of the on-axis response in all but very large rooms. However, spl contour lines above 5kHz reveal that the soft-dome tweeter is rather beamy. This too will compensate for the on-axis energy excess in the same region, but, again, to a much smaller extent in larger rooms. I do note that LG listened to the Charios in both his large and small listening rooms.
Fig.4 Chario Academy One, horizontal 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.
Plotting a similar graph in the vertical plane (fig.5) shows that sitting with your ears even just a small distance above the Chario's tweeter axis results in a severe suckout in the crossover region and a lack of top-octave energy. I suspect that this at least partly explains LG's auditioning findings. Tom Norton's research for Stereophile has shown that a listener in a typical chair or sofa sits with his or her ears between 34" and 39" from the floor; I note that LG's ear height of 37" falls exactly in the center of this range. (A "director's chair," by the way, increases this to between 40" and 45".) Unless the Chario Academy One is placed on very tall stands30", saythe listener will not perceive an optimal balance, particularly in a fairly large room like LG's.
Fig.5 Chario Academy One, vertical response family at 50", normalized to response on tweeter axis, from back to front: response 20°5° above-axis; reference response; response 5°$10° below-axis.
In the time domain, the Academy One's step response (fig.6) reveals that the speaker's tweeter leads its woofer by 0.3ms or so, and that both are connected with the same positive acoustic polarity. The associated cumulative spectral-decay plot (fig.7) is superbly clean, with only a very small degree of hash present at the top of the woofer's passband. No wonder LG found this speaker to sound so smooth.John Atkinson
Fig.6 Chario Academy One, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth).
Fig.7 Chario Academy One, cumulative spectral-decay plot at 50" (0.15ms risetime).