Tower Speaker Reviews

Measurements performed by John Atkinson

The sensitivities and impedances of the ATC Concept 7 loudspeakers were not measured: In a speaker system with integrated amplifiers, neither is relevant. The amplifiers are designed to work together with the individual drive-units to provide optimal performance.

The frequency response of the L/R/surround speaker, shown in Fig.1, is about as linear as modern loudspeakers get. JGH's single criticism of the speakers was that they exhibited a slight lack of lower-midrange fullness and natural high-end bite with certain instruments. The small dip at 300Hz, and a larger one averaging about 3dB between 3kHz and 6kHz, might explain either or both of these observations. The bass, as Gordon notes, holds up strongly to 40Hz.

Fig.1: ATC SCM 70ASL, anechoic response on tweeter axis at 50", averaged across a 30° horizontal window and corrected for microphone response, combined with nearfield woofer and port responses (2ohms/vertical.

The lateral dispersion is good, with the response falling off rapidly but smoothly as the listener moves farther off-axis. The vertical dispersion is even as long as the listener's ear height is relatively close to the tweeter axis.

Though we seldom print it in our "Measurements" sidebars, we usually mention in passing a speaker's delayed resonance, or "waterfall," plot. This time, the absence of our usual impedance plots leaves space for us to reproduce the SCM 70ASL's waterfall plot (Fig.2), the curves of which indicate how the speaker's response dies away when the driving signal is switched off. A perfect speaker would show a single curve at the 0.00 second point, then a dropoff to nothing as time elapses. Perfection is impossible in the real world, however. The results in Fig.2, while not the best we have measured, are good.

Fig.2: ATC SCM 70ASL, delayed resonances.

The frequency response of the SCM 2C70ASL center-channel is shown in Fig.2. There is a little extra midbass in comparison with the SCM 70ASL. (Both speakers are ported, but the center-channel's small ports operate as pressure-relief vents and contribute little to the speaker's bass extension.) The middle treble dip is also absent in the center-channel, suggesting a slight difference between the crossover designs of the two speakers. Altogether, however, this is also a fine result. We did not measure the dispersion of the center-channel speaker beyond the 30° averaged window reflected in Fig.3 because the speaker's size and weight made this logistically impossible without incurring a hernia!

Fig.3: ATC SCM 2C70ASL, anechoic response on tweeter axis at 50", averaged across a 30° horizontal window and corrected for microphone response, combined with nearfield woofer response (2ohms/vertical div.).

The delayed resonance plot of the SCM 2C70ASL is shown in Fig.4. It is a little less clean than the plot for the SCM 70ASL in Fig.3, with a noticeable resonance at just under 6kHz.

Fig.4: ATC SCM 2C70ASL, delayed resonances.

Nothing in the measured performance of the ATC Concept 7 system deserves more than a moment's reflection: It's a solid set of results that in no way contradicts JGH's strongly (to say the least) positive comments.—TJN