Aerial Acoustics CC3 center loudspeaker Of all the lousy labs in the world...

Sidebar 3: Of all the lousy labs in the world...

A quick check on the CC-3's B-weighted sensitivity revealed it to be within spitting distance of the 86dB/W/m 10T at 84.5dB/W/m. The 1.5dB difference is basically inconsequential. Its impedance with the tone controls set to their worst-case positions—Program = "0," Environment = "+"—drops below 4 ohms in the midrange (fig.1) but is otherwise not too demanding. The peak at 53Hz reveals the tuning of the sealed box.

Fig.1 Aerial Acoustics CC3, worst-case electrical impedance (solid) and phase (dashed) (Program = 0, Environment = +) (2 ohms/vertical div.).

Fig.2, which shows the individual responses of the CC3's twin woofers (left) and the midrange/tweeter section (right), indicates that the woofers' –6dB point lies lower than expected at 39Hz, but this appears to be achieved by building in a slight boost through the upper bass. (This apparent boost is partly an artifact of the nearfield measurement technique, which assumes a 2pi rather than an anechoic environment. However, I believe this is not an unreasonable assumption in the bass, due to the proximity of room boundaries, well within a single wavelength.) The crossover to the single midrange unit lies at 550Hz, a little higher than specified. Dominating the ultrasonic region in fig.2 is a peak due to the metal-dome tweeter's "oil-can" resonance. At 25.4kHz, however, this will not have any audible side effects.

Fig.2 Aerial Acoustics CC3, acoustic crossover on HF axis at 50", corrected for microphone response, with nearfield woofer and midrange responses plotted below 3.5kHz and 500Hz, respectively.

This peak can also be seen in the plot of the CC3's overall response on the tweeter axis with the tone controls set to their "0" positions (fig.3). Other than the aforementioned rise in the upper bass, the balance is pretty smooth, though with a slight but broad presence-region emphasis. WP noted that the CC3 integrated well with the 10T left and right speakers he used. Fig.4 shows the response of the Aerial 10T taken under identical conditions. It is, indeed, both similar to that of the CC3 and respectably flat.

Fig.3 Aerial Acoustics CC3, anechoic response on tweeter axis at 50", averaged across 30° horizontal window and corrected for microphone response, with nearfield woofer response plotted below 300Hz.

Fig.4 Aerial Acoustics 10T, anechoic response on tweeter axis at 50", averaged across 30° horizontal window and corrected for microphone response, with complex sum of nearfield woofer and port responses plotted below 300Hz.

As WP notes, the arrangement of the drive-units on the CC3's front baffle is intended to minimize the off-axis comb filtering typical of center-channel home-theater speakers with multiple drive-units handling the same frequency regions. Fig.5 shows how the CC3's response changes to the sides of the tweeter axis. (Only the changes in response are shown in this graph, which means that the on-axis response appears to be a straight line.) A slight interference-related off-axis suckout can be seen in the lower midrange, but this is mild compared with typical "THX" designs and lower in frequency. Other than that, the CC3's horizontal dispersion smoothly reduces with increasing frequency—excellent!

Fig.5 Aerial Acoustics CC3, 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.

Vertically (fig.6), it can be seen that the balance only changes to a moderate degree between the tweeter axis and up to 10° below that axis. With the CC3 placed above the screen, a moderate amount of tiltdown is appropriate. But if placed below the screen, make sure it is tilted up to bring the listeners' ears on to the tweeter axis.

Fig.6 Aerial Acoustics CC3, vertical response family at 50", normalized to response on tweeter axis, from back to front: differences in response 45°–5° above axis; reference response; differences in response 5°–45° below axis.

In the time domain, the step response (fig.7) indicates that the drive-units are all connected with the same positive acoustic polarity, but that the speaker is not time-coherent. This was expected from the flat baffle and high-order crossover: its subjective significance is uncertain. The related cumulative spectral-decay, or waterfall plot (fig.8), is impressively clean, and even better than that of the 10T, which showed a low-level ridge of resonant energy at 3.2kHz. There is a suggestion of a slight step at the cursor position in this graph—just below 2kHz—that, all things being equal, might correlate with a very slight nasality to the speaker's character. However, I note that WP was not bothered by anything like this.

Fig.7 Aerial Acoustics CC3, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth).

Fig.8 Aerial Acoustics CC3, cumulative spectral-decay plot at 50" (0.15ms risetime).

Finally, I examined the vibrational behavior of the CC3's enclosure with a simple plastic-tape accelerometer. As should be expected from the speaker's massive, well-braced construction, what resonant modes there are are low in level and high in frequency, both factors minimizing the possibility of any subjective problems. Fig.9 shows a typical waterfall plot calculated from the output of the accelerometer. The only modes apparent are at 500Hz and 420Hz, these also found on the other panels. They are low in level, however.

Fig.9 Aerial Acoustics CC3, cumulative spectral-decay plot of accelerometer output fastened to back of enclosure (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz).

In summary, these measurements indicate that the CC3, like the 10T, is a well-engineered loudspeaker. I'm not surprised that WP liked it. What does surprise me, as Wes pointed out, is how few loudspeaker companies recognize the important contribution made by the center speaker to the overall quality of a home-theater system. The CC3 is definitely a wake-up call in this area.—John Atkinson

Aerial Acoustics Corporation
P.O. Box 81248
Wellesley Hills, MA 02181

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