Aperion Verus Grand Bookshelf loudspeaker Measurements
Sidebar 3: Measurements
I examined the performance of the Aperion Verus Grand Bookshelf loudspeaker with DRA Labs' MLSSA system, using a calibrated DPA 4006 microphone to measure the speaker's frequency response in the farfield, and an Earthworks QTC-40 mike for the nearfield responses. The Verus Grand's voltage sensitivity is specified as 87dB; my estimate was close, at 86.3dB(B)/2.83V/m. The speaker's nominal impedance is 6 ohms, but other than the region between 120 and 400Hz, where it reaches a minimum of 4.15 ohms at 160Hz, the impedance magnitude remains above 6 ohms across the audioband. While there is a combination of 6 ohms and 40° electrical phase angle at 120Hz, a good, 8 ohmrated amplifier or receiver should have no difficulty driving the Verus Grand.
The traces in fig.1 are free from the small discontinuities that would suggest the presence of cabinet resonances. However, investigating the vibrational behavior of the enclosure panels with a simple plastic-tape accelerometer did uncover a strong resonance at 516Hz on all surfaces, especially the sidewalls (fig.2), as well as a lower-level mode at 406Hz. It's possible that the 516Hz mode is too high in frequency and the 406Hz mode too low in level to affect the Aperion's sound quality.
The green trace in fig.3 is the tweeter's on-axis response, taken without the grille. The Verus Grand's tweeter appears to be set a couple of dB too high in level compared with the woofer (blue trace), which correlates with BJR's finding that the speaker's upper registers "sparkled," with percussive transients "appropriately fast." The crossover to the woofer is set low, at 1240Hz; the tweeter's relatively limited dynamic range below 2kHz might have led to BJR's finding the piano's upper register to seem a bit forward. Although the woofer appears to peak a little in the upper bass, this is entirely a function of the nearfield measurement technique. The port's output (red trace) peaks between 40 and 100Hz, with the corresponding minimum-motion notch in the woofer's output occurring at 59Hz, suggesting only moderate bass extension. The port's midrange output is commendably free from resonances.
The blue trace in fig.4 shows the farfield response of the Verus Grand Bookshelf without its perforated metal grille, averaged across a 30° horizontal window centered on the HF axis. BJR preferred the sound of the Verus with the grille in place; this is shown by the red trace in this graph. The treble response is indeed a little more even with the grille on. Again, the apparent rise in response in the upper bass is a measurement artifact. The speaker is maximally flat in the upper bass, with its output down 6dB at the port tuning frequency.
The apparent presence-region flare in the horizontal-dispersion pattern (fig.5), indicated by the cursor position, is due in part to the small dip on axis between 2 and 4kHz filling in to the speaker's sides. But it might also add to the forward presentation of the piano's upper registers. Other than that, the horizontal radiation pattern is even, with the top octaves not falling off to the sides as much as with conventional 1" dome tweeters. In the vertical plane (fig.6), the Aperion maintains its balance over a wide angle.
The Verus Grand Bookshelf's step response on the tweeter axis (fig.7) reveals that both drive-units are connected with positive acoustic polarity. I initially thought that because the decay of the tweeter's step doesn't quite blend with the start of the woofer's step, the optimal listening axis is just below the tweeter axis. However, the discontinuity is actually present in the tweeter's output when the latter is examined on its own; perhaps it is a reflection of the small plate that supports what appears to be a secondary suspension at the center of the dome. The cumulative spectral-decay plot (fig.8) is clean, and free from delayed resonance energy.
Aperion's Verus Grand Bookshelf offers superb measured performance; though that slightly elevated tweeter level adds air and sparkle, it needs to be taken into account when matching the speaker with the other components in a system.John Atkinson