With two woofers loaded by two ports, and a midrange unit in its own subenclosure loaded by a third port, the Amati Homage's behavior in the midrange and bass is complex. Fig.4 shows the responses, measured in the nearfield, of all of these radiating elements. The top trace to the right in fig.4 is the midrange unit. This can be seen to slope up through the mids, but with a slight peak in its output at 70Hz. The trace just above the midrange unit at this frequency is the output of the twin woofers, this covering the 30-180Hz bandpass, with the reflex notch at a low 20Hz. The top trace to the right of the graph is the output of the woofer ports—very broad, and somewhat suppressed in level. Finally, the lower trace that peaks at the same 70Hz frequency where the midrange unit has a peak is the output of the midrange port. While all of these radiators seem well behaved outside their passbands, their broad overlap will complicate any predictions about the Amati's overall bass behavior.
Fig.4 Sonus Faber Amati Homage, low-frequency acoustic crossover, measured in the nearfield.
To the left in fig.5 is shown the complex sum (amplitude, phase, and distance from the mike, assuming a nominal farfield mike position) of the individual responses shown in fig.4. The coincidence of the woofers and midrange unit in the upper bass appears to give a peak at 65Hz, with what is more like a sealed-box, 12dB/octave rolloff below that frequency. An enigma!
Fig.5 Sonus Faber Amati Homage, 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, midrange, and port responses plotted below 300Hz.