Infinity Intermezzo 2.6 loudspeaker Measurements

Sidebar 3: Measurements

With its powered woofer, the Infinity Intermezzo 2.6's impedance plot (fig.1) shows just the tweeter's electrical characteristics. It reaches a minimum value of 5.95 ohms at 18kHz, which is benign. However, the high-pass crossover gives rise to quite an extreme phase angle in the mid-treble, which will result in the speaker being a harder load to drive than otherwise would be the case. On the other hand, my estimate of its voltage sensitivity was 89.3dB(B)/2.83V/m, which is significantly higher than average.

Fig.1 Infinity Intermezzo 2.6, electrical impedance (solid) and phase (dashed). (2 ohms/vertical div.)

The metal enclosure was reasonably well-damped and -braced, but a resonant mode at 254Hz could be detected on all surfaces (fig.2). This mode is low enough in frequency and high enough in level that I would have expected it to degrade lower-midrange clarity. MF noted nothing amiss in this region, but perhaps this mode is connected with the slightly unstable imaging he noted with mono recordings.

Fig.2 Infinity Intermezzo 2.6, cumulative spectral-decay plot of accelerometer output fastened to center of top panel. (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz.)

Fig.3 shows the Intermezzo's frequency response averaged across a 30 degrees lateral window on the tweeter axis. Some of the apparent rise in the bass will be due to the nearfield measurement technique used to assess the speaker's low-frequency behavior. However, most of it is real, the farfield behavior looking very similar. (The woofer control was set to "10" for this measurement; lowering it seemed to hinge down the midbass rather than reduce the upper-bass peak.) The trace with the more restricted extension was taken with the Infinity's high-pass filter switched in; compared with the maximum level, it reaches its 3dB-down point at almost exactly 80Hz, and rolls off at 24dB/octave below that point. Both aspects make it ideal for use with a subwoofer.

Fig.3 Infinity Intermezzo 2.6, anechoic response on tweeter axis at 50", averaged across 30 degrees horizontal window and corrected for microphone response, with the nearfield woofer response plotted below 300Hz with (bottom) and without (top) high-pass filter engaged.

Moving higher in frequency in fig.3, the midrange is depressed by a couple of dB with respect to the treble. Whether this balance is heard as a laid-back midrange or an elevated lower treble will depend on the listener's taste and the music listened to. Michael did note that he found the Intermezzo's presence region to sound a little boosted. The overall response trend is very smooth, however, and the high-amplitude resonance of the metal-dome tweeter is too high in frequency, at almost 30kHz, to have any subjective consequences.

A speaker's perceived in-room balance will be significantly affected by its dispersion, particularly in the horizontal plane. The Intermezzo 2.6's lateral radiation pattern is shown in figs.4 and 5, the former showing the actual responses (though not corrected for the measuring microphone's departure from flatness), the latter just the differences between the off-axis responses and the tweeter-axis response. You can see from the even spacing of the contour lines in this 3-D plot how even and well-controlled the speaker's dispersion is—something that correlates with stable, accurate perceived imaging. That MF was bothered by the stability of dual-mono imaging can't be laid at the door of the speaker's dispersion, which is why I wondered if it was actually due to enclosure resonances.

Fig.4 Infinity Intermezzo 2.6, lateral response family at 50", from back to front: responses 90 degrees-5 degrees off-axis on wooden trim side of baffle, reference response on tweeter axis, responses 5 degrees-90 degrees off-axis on drive-unit side of baffle.

Fig.5 Infinity Intermezzo 2.6, lateral response family at 50", normalized to response on tweeter axis, from back to front: differences in response 90 degrees-5 degrees off-axis on wooden trim side of baffle, reference response, differences in response 5 degrees-90 degrees off-axis on drive-unit side of baffle.

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