Aerial Acoustics 5T loudspeaker Measurements

Sidebar 3: Measurements

I used DRA Labs' MLSSA system and a calibrated DPA 4006 microphone to measure the Aerial 5T's frequency response in the farfield, and an Earthworks QTC-40 for the nearfield and in-room responses. The 5T's voltage sensitivity is specified as 87dB/2.83V/m; my estimate was somewhat lower, at 85.2dB(B). The Aerial's nominal impedance is specified as 4 ohms, with a minimum magnitude of 3 ohms. My measurement was significantly different, with a magnitude (fig.1, solid trace) that dipped below 6 ohms in just two regions—between 29 and 54Hz and between 110 and 310Hz—and a minimum value of 4.28 ohms at 160Hz. The electrical phase angle (fig.1, dotted trace) is occasionally extreme, and the combination of 6 ohms and –38° at 108 ohms means a good 4 ohm–rated amplifier would be the best match for this speaker. The impedance traces are also unusual in that they seem atypical of a two-way design, which usually has a single impedance peak in the low treble due to the crossover filters. The 5T's magnitude trace has a second peak, centered on 5kHz, that suggests the presence of some sort of equalization network.

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

The impedance traces are free from the discontinuities that would imply the presence of cabinet-panel resonances, and the 5T's graceful-looking enclosure was indeed inert. The only resonant modes I could find, present on the top panel and both sidewalls, lay at 594Hz (fig.2), but these were very low in level.

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

The saddle centered just below 40Hz in the impedance-magnitude trace suggests that the tuning frequency of the slot port on the front baffle lies in this region. A nearfield measurement of the woofer's output (fig.3, blue trace) reveals a minimum-motion notch at 38Hz. This is the frequency at which the woofer cone is held stationary by the back pressure from the port resonance, and the port's output (fig.3, red trace) does peak broadly between 20 and 100Hz. However, a strong peak between 700 and 800Hz in the port's response coincides with a small suckout in the woofer's farfield output (blue trace above 350Hz). The woofer crosses over to the tweeter (green trace) close to the specified 2.7kHz with steep filter slopes.

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Fig.3 Aerial 5T, acoustic crossover on tweeter axis at 50", corrected for microphone response, with nearfield responses of woofer (blue) and port (red), respectively plotted in the ratios of the square roots of their radiating areas below 300Hz and 1kHz.

The tweeter appears to be set 2–3dB too high in level, but when the 5T's farfield response is averaged across a 30° horizontal window (fig.4) the speaker's treble response is superbly flat. However, there is a complicated pattern of small peaks and suckouts between 500Hz and 1.5kHz, perhaps related to the port resonance noted above. The rise in the upper bass is due to the nearfield measurement technique, which assumes a 2pi acoustic environment. The Aerial 5T's ported woofer alignment is tuned for articulation rather than boom.

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Fig.4 Aerial 5T, 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.

The plot of the Aerial's lateral dispersion (fig.5) reveals that its output above 7kHz does drop off rapidly to the speaker's sides. The contour lines in this graph are smooth, though the slight excess of energy to the speaker's sides in the low treble might make the 5T sound slightly bright in live rooms. In the vertical plane (fig.6), a suckout develops in the crossover region more than 5° above the tweeter axis, which suggests that the Aerial be used on high rather than low stands.

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Fig.5 Aerial 5T, lateral 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.

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Fig.6 Aerial 5T, 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.

The 5T's spatially averaged in-room response (fig.7, red trace, taken with the speakers in the initial positions in the room) shows a generally smooth balance, though there is a slight excess of energy in region where the lateral-dispersion plot showed a slight off-axis flare. Compared with the BBC LS3/5a (blue trace), the Aerial lacks the small peak between 1 and 2kHz, which adds a touch of nasality to the LS3/5a's sound, but the American speaker's limited top-octave dispersion results in less high-treble energy in-room. At the other end of the spectrum, the Aerial has more upper bass, but its ported alignment results in a faster rolloff in the midbass and below. In both respects, the 5T resembles the KEF LS50 (green trace).

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Fig.7 Aerial 5T, spatially averaged, 1/6-octave response in JA's listening room (red); of KEF LS50 (green); and of BBC LS3/5a (blue).

Compared with the Bowers & Wilkins 805 D3, which I also review in this issue (fig.8, blue trace), the Aerial 5T (red) has a similar in-room response to the British speaker in the midrange and upper bass, but more energy in the midbass and below. It lacks the B&W's depressed presence region, but the mid- and upper-treble regions are significantly lower in level. The two speakers did indeed sound as you would expect from this graph. With my room's increasing absorptivity in the treble, while the Aerial's balance was not as "brilliant" as the B&W's, the 5T's was closer to being truly neutral.

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Fig.8 Aerial 5T, spatially averaged, 1/6-octave response in JA's listening room (red) and of Bowers & Wilkins 805 D3 (blue).

In the time domain, the Aerial's step response on the tweeter axis (fig.9) reveals that both of its drive-units are connected in positive acoustic polarity, but the tweeter's step blends smoothly with the woofer's. The 5T's cumulative spectral-decay plot (fig.10) features superbly clean decay throughout the treble, but some delayed energy at the frequencies of the small peaks in the upper midrange in the quasi-anechoic farfield response.

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Fig.9 Aerial 5T, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth).

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Fig.10 Aerial 5T, cumulative spectral-decay plot on tweeter axis at 50" (0.15ms risetime).

Other than its port's peaky midrange output, Aerial's 5T demonstrates excellent speaker engineering.—John Atkinson

COMPANY INFO
Aerial Acoustics Corporation
100 Research Drive
Wilmington, MA 01887
(978) 988-1600
ARTICLE CONTENTS

COMMENTS
georgehifi's picture

Wonder if that's fixable with a resistive port plug?

Cheers George

Allen Fant's picture

Excellent review -JA.
Happy Listening!

Johan Stam's picture

As a European I know I should tread carefully here, but is this a roundabout way of saying that all parts are actually manufactured in China? If so, why not just get over it and enjoy the 5T for what it is, judging by your review: a magnificent loudspeaker.

Cheers, Johan

jporter's picture

I really like the Elac UB5's. You have heard both. How would the Elac's compare to these...Thanks

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