Aerial Acoustics Model 5 loudspeaker Measurements

Sidebar 3: Measurements

The Aerial 5 is a moderately difficult load to drive. Although the impedance magnitude (fig.1) shows an impedance minimum of 4.3 ohms and a value above 8 ohms over most of the band, the Aerial 5's lowish 84.5dB B-weighted sensitivity suggests the loudspeaker should be used with a well-powered amplifier. Fig.1 is notable for the lack of any wrinkles in the impedance magnitude curve, indicating that the enclosure is quite rigid. The sealed-box tuning at 65Hz is accompanied by the impedance peak at that frequency. This usually corresponds to the loudspeaker's -6dB point.

Fig.1 Aerial 5, electrical impedance (solid) and phase (dashed) (2 ohms/vertical div.).

Fig.2 shows the individual responses of the Aerial 5's drivers. The slight bass rise is partially a function of the nearfield measurement technique, but one that JA feels accurately reflects a loudspeaker's performance in all but very large rooms. Nonetheless, the measurement (and auditioning) suggests that the Aerial 5, unlike the Tukan, should be placed well out into the room. Fig.2 also shows steep crossover slopes, and a crossover frequency of 2.4kHz. The drivers are well-behaved out-of-band. This measurement was made on the optimal axis, with the 5 tilted back.

Fig.2 Aerial 5, acoustic crossover on optimal axis at 50", corrected for microphone response, with nearfield woofer response plotted below 300Hz.

The 5's response, averaged over a 30 degrees lateral window on the optimal axis with the speaker tilted back (fig.3), shows the Aerial to be remarkably flat. The midband is free from large peaks and dips, and the treble doesn't exhibit the common rise in the top octave. My impressions of an uncolored sound and super-smooth treble correspond well with fig.3.

Fig.3 Aerial 5, anechoic response on optimal axis at 50", averaged across 30 degrees horizontal window and corrected for microphone response, with nearfield woofer response plotted below 300Hz.

Fig.4 shows the 5's vertical response family normalized to the tweeter axis. This means the response on the tweeter axis is shown as a straight line, the other curves showing the deviation from the tweeter-axis response. The measurement indicates that listening height is crucial to getting the best sound from the 5; crossover suckouts appear in the response above and below the optimal axis. Fortunately, the front spike adjusts the amount of tiltback for fine-tuning the 5s to your listening height and distance.

Fig.4 Aerial 5, vertical response family at 50", normalized to response on tweeter axis, from back to front: differences in response 45 degrees-5 degrees above tweeter axis; reference response; differences in response 5 degrees-45 degrees below tweeter axis.

The 5's lateral dispersion (fig.5) reveals that the loudspeaker has superb control over its dispersion. In other words, the response as you move off-axis remains smooth and flat, with the expected treble rolloff. Such near-perfect behavior is difficult to achieve. The sidewall reflections will be less colored with the 5 than with other loudspeakers whose response changes off-axis. The 5's smooth dispersion usually equates with well-defined imaging. The near-perfect dispersion is marred only by a slight "flare" at the bottom of the tweeter's passband, seen as the bump in the response just above 2kHz.

Fig.5 Aerial 5, horizontal response family at 50", normalized to response on optimal axis, from back to front: differences in response 90 degrees-5 degrees off-axis; reference response; differences in response 5 degrees-90 degrees off-axis.

Although the 5's spike arrangement tilts the loudspeaker back, it is not time-coherent—the step response of fig.6 shows the tweeter energy arriving first. Both drivers are connected with the same polarity. Fig.7 shows the Aerial 5's cumulative spectral-decay or waterfall plot. The decay is quick and very clean, corresponding well with my listening impressions. There is just a hint of stored energy at the top of woofer band, seen as the ridge at 2.4kHz. Overall, this is superlative performance.

Fig.6 Aerial 5, step response on optimal axis at 50" (5ms time window, 30kHz bandwidth).

Fig.7 Aerial 5, cumulative spectral-decay plot at 50" (0.15ms risetime).

Not surprising in light of the 5's sturdy build and small enclosure, the cabinet was relatively free from resonances. Using an accelerometer to measure cabinet resonances (fig.8), we can see that the side-panel resonance is low in amplitude and high in frequency—both good conditions. (The high frequency of the resonance makes it less likely to be audible.) Measurements taken on other cabinet panels produced similar results. Such exemplary cabinet behavior correlates with my impression of a clean and articulate bass sound.

Fig.8 Aerial 5, cumulative spectral-decay plot of accelerometer output fastened to center of side panel. (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz.)

Overall, the Aerial 5 is a very well-engineered product. The on-axis flatness, smooth dispersion pattern, clean waterfall plot, and stiff cabinet all indicate that designer Michael Kelly has done his homework.—Robert Harley

Aerial Acoustics
P.O. Box 81248
Wellesley Hills, MA 02181
(617) 235-7715