Sonus Faber Concerto Grand Piano loudspeaker Measurements part 2
Fig.4 Sonus Faber Concerto Grand Piano, anechoic response on tweeter axis at 50", averaged across 30 degrees horizontal window and corrected for microphone response, with the complex sum of the nearfield woofer and radiator responses plotted below 300Hz.
If the speaker's on-axis response in the crossover region is a little wayward, why didn't MF notice this? The answer to a question like this is almost always found in a speaker's dispersion, and fig.5, which shows just the changes in the Grand Piano's output to its sides, reveals that where there is an on-axis suckout there is an off-axis peak, and vice versa. At a typical distance in a typical room, where the listener's perception of a speaker's balance is contributed to roughly equally by both the on-axis and power responses, the Sonus Faber will sound evenly balanced through the mid-treble region. In the top octave, the tweeter's output can be seen to fall quite rapidly to the speaker's sides. For interest's sake, fig.6 shows the actual off-axis responses rather than the differences in response. Despite the limited lateral dispersion above 10kHz, the tweeter's on-axis peak in this region persists over quite a wide window, which explains why MF found that the Grand Piano featured a high-frequency rise.
Fig.5 Sonus Faber Concerto Grand Piano, horizontal response family at 50", normalized to response on tweeter 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.
Fig.6 Sonus Faber Concerto Grand Piano, horizontal response family at 50", from back to front: response 90 degrees-5 degrees off-axis; response on tweeter axis; response 5 degrees-90 degrees off-axis.
Vertically, fig.7 reveals that a crossover-region suckout quickly appears above the tweeter axis. (Again, just the differences are shown in this graph.) This is a reasonable 34" from the floor without the optional stone base, but Sonus Faber owners should experiment with tiltback to get the best balance.
Fig.7 Sonus Faber Concerto Grand Piano, vertical response family at 50", normalized to response on tweeter axis, from back to front: differences in response 15 degrees-5 degrees above-axis; reference response; differences in response 5 degrees-15 degrees below-axis.