Aperion Audio Intimus 6T loudspeaker Measurements
Aperion specifies the Intimus 6T's voltage sensitivity as a high 91dB/2.83V/m. My B-weighted estimate on the speaker's tweeter axis was slightly lower than that, at 89.6dB(B)/2.83V/m, but this is still usefully higher than average. The loudspeaker's impedance ranges between 4 and 6 ohms over most of the audioband, with a combination of 5 ohms and 45° electrical phase angle at 75Hz, meaning that a good 4 ohmrated amplifier or receiver should be used with the Aperions.
The traces in fig.1 are free from the severe glitches that would suggest the presence of cabinet panel resonances. However, investigating the enclosure's vibrational behavior with a plastic-tape accelerometer, I found strong resonances at 281, 359, and 555Hz on all surfaces (fig.2). These are low enough in frequency and high enough in amplitude that, taking into consideration the radiating areas involved, I would have expected a degree of midrange congestion to be audible.
Fig.1 Aperion Intimus 6T, electrical impedance (solid) and phase (dashed). (2 ohms/vertical div.)
Fig.2 Aperion Intimus 6T, cumulative spectral-decay plot calculated from output of an accelerometer fastened to side panel 10" from top (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz).
The saddle centered on 30Hz in the impedance-magnitude trace suggests that this is the tuning frequency of the 2.5"-diameter port on the front baffle; the sum of the two woofer outputs, measured in the nearfield, does have a well-defined minimum-motion notch at 29Hz (fig.3, blue trace). The upper and lower woofers have identical upper-frequency responses, but one has a port-loading notch slightly lower in frequency than the other, suggesting some variability in specific drive-unit parameters. The port output (fig.3, red) peaks as expected between 20 and 50Hz, implying good low-frequency extension, as BJR found, and offers a smooth rolloff above that region. However, a pipe resonance of some kind can be seen just below 1kHz. There is only a slight hint of the upper-bass boost in this graph that results from the nearfield measurement technique, suggesting that the 6T's tuning is slightly overdamped.
Fig.3 Aperion Intimus 6T, anechoic response on tweeter axis at 50" without grille (black), averaged across 30° horizontal window and corrected for microphone response, with nearfield responses of woofer (blue) and port (red), plotted in the ratios of the square roots of their radiating areas below 300Hz and 1kHz, respectively, and the complex sum of their nearfield responses plotted below 300Hz (black).
Higher in frequency in fig.3, the woofers' farfield response peaks a little between 900 and 1800Hz, which will aid the speaker's presentation of recorded detail, with then a slight crossover-region suckout apparent on the tweeter axis. The silk-dome tweeter is flat within its passband, rolling above 16kHz or so. The speaker's plot of lateral dispersion (fig.4) indicates that the 6.5" woofers get a little directional just below the crossover, leading to an off-axis flare at the base of the tweeter's passband. Unfortunately, this flare is just a little too high in frequency to compensate, at least in smallish rooms, for the on-axis suckout. It is possible that the Intimus 6T will sound a little bright in all but very large or very well-damped rooms. However, the tweeter gets increasingly directional above 8kHz, which might make the speaker's balance tend toward a lack of top-octave air. I note that BJR did comment that he didn't hear as much high-frequency air as usual. In the vertical plane (fig.5), the crossover suckout deepens below the tweeter axis, which is around 38" from the floor. Best not to slouch when you listen to this speaker.
Fig.4 Aperion Intimus 6T, lateral response family at 50", normalized to response on tweeter axis, from back to front: differences in response 905° off axis, reference response, differences in response 590° off axis.
Fig.5 Aperion Intimus 6T, vertical response family at 50", normalized to response on tweeter axis, from back to front: differences in response 155° above axis, reference response, differences in response 515° below axis.
The Aperion 6T's step response (fig.6) reveals that the tweeter is connected in inverted acoustic polarity and the woofers in positive polarity, the former leading the latter by about 0.5ms. Correlating with the crossover-region suckout in the tweeter-axis response, the positive rise in the woofers' step occurs a little too late for good integration with the return to the zero line of the tweeter's step. Though it is a little difficult to see in the speaker's farfield cumulative spectral-decay plot (fig.7), this results in some delayed energy in the same region. Though the region covered by the tweeter in this graph shows an impressively clean decay, there is a slight step evident at 4.48kHz.
Fig.6 Aperion Intimus 6T, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth).
Fig.7 Aperion Intimus 6T, cumulative spectral-decay plot on tweeter axis at 50" (0.15ms risetime).
At $1390/pair, Aperion's Intimus 6T doesn't measure appreciably better than the Intimus 533-T, at half the price but no longer available, and which Bob Reina reviewed in April 2007. It does go deeper in the bass, however, and, all things being equal, its two 6.5" woofers should play louder with less strain than the 533-T's twin 5.25" drive-units. The Intimus 6T is also very well finished.John Atkinson