Audio Physic Avanti III loudspeaker Measurements
The Audio Physic Avanti III's B-weighted sensitivity was a fairly high 88.6dB(B)/2.83V/m, fractionally but insignificantly below the specified 89dB/W/m. However, its plot of impedance magnitude and phase against frequency (fig.1) revealed it to be a "4 ohm" design; ie, it actually draws 2W from the amplifier to raise the rated sound-pressure level. The speaker's minimum impedance is around 3.5 ohms in the low bass and upper midrange, which should not present problems to good 4 ohm-rated amplifiers. While the phase angle is generally benign, there is a coincidence of low impedance and high phase angle around 20Hz. Fortunately, with the exception of classical organ recordings, there is rarely any significant music energy down there—but the Avanti would hardly be the speaker of choice for fans of organ CDs, in any case.
Fig.1 Audio Physic Avanti III, electrical impedance (solid) and phase (dashed). (2 ohms/vertical div.)
The traces in fig.1 are free from discontinuities that might otherwise indicate the presence of cabinet resonances. Unfortunately, an equipment failure meant I could not perform any accelerometer measurements of the Audio Physic's beautifully curved enclosure walls. However, listening to the cabinet with a stethoscope while the speaker reproduced swept sinewaves and pink noise indicated that it was basically free from vibrational resonances.
The Avanti's downward-firing ports mean that the exact tuning of the reflex-loaded woofers will change according to the gap between the base of the speaker and the floor. For my measurements, I placed the speaker's feet on 1" blocks of Styrofoam, which gave the saddle centered at 29Hz in the fig.1 magnitude trace, indicating the ports' tuning frequency. But there are some other twists in the traces between 40Hz and 160Hz that suggest something else is going on.
On the left side of fig.2 are shown the individual responses of the side-mounted woofers and the downward-firing ports, taken in the nearfield; ie, with the microphone capsule very close to the radiating element. (To measure the port, I placed the mike on the floor, adjacent to the edge of the cabinet.) As expected, the minimum in the woofer response at 29Hz coincides with both the maximum in the port output and the frequency of the bass saddle in fig.1.
Fig.2 Audio Physic Avanti III, anechoic response on tweeter axis at 50", averaged across 30 degrees horizontal window and corrected for microphone response, with the nearfield woofer and port responses plotted below 750Hz and 275Hz, respectively.
But look at the notch around 100Hz in the woofer and port responses. There is presumably some kind of anti-resonance at this frequency, and it shows up as well in the complex sum (taking magnitude, phase, and physical separation of the drivers into account) of the port, woofer, and midrange outputs (top trace in fig.2 below 350Hz). Both ports and woofers can be seen to roll off smoothly above their passbands, however, and while there is a suggestion of a peak in the woofer response at 500Hz, this is suppressed by the crossover. (The changeover between the woofers and the midrange units appears to be set at 200Hz.) That Michael found the bass a little lean comes as no surprise; the ports seem to be doing little to support the speaker's midbass output.
Higher in frequency (fig.2), the Avanti is basically extremely flat in its tweeter-axis response. However, very slight lacks of energy can be seen in the lower midrange and at 4kHz. The former occurs in a region where the frequency resolution of my quasi-anechoic measurement technique is poor. This is also the lower crossover region, and a region where the room acoustics and boundary conditions will have an effect. Nevertheless, it does look like the upper midrange is slightly exaggerated; in my own auditioning of the Avanti in Michael's room, I felt its balance to be slightly on the forward side.
The Avanti's use of small-diameter midrange units, a narrow baffle, and sensible crossover implementation endows the speaker with superb lateral dispersion (fig.3). The even spacing of the contour lines in this graph and the smooth, well-controlled off-axis rolloff in the top two audio octaves are virtually textbook; no wonder MF found the Avantis to offer "incredible image focus and soundstaging precision," something I heard for myself in his room.
Fig.3 Audio Physic Avanti III, lateral 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.
In the vertical plane (fig.4), the response doesn't change significantly over quite a wide angle, though if you sit very low, a suckout begins to appear at the upper crossover frequency.
Fig.4 Audio Physic Avanti III, vertical response family at 50", from back to front: differences in response 15 degrees-5 degrees above tweeter axis, reference response, differences in response 5 degrees-15 degrees below tweeter axis.