Acarian Aln Petite loudspeaker & PW-1 woofer system Measurements

Sidebar 5: PW-1 Measurements

With its twin 6.5" drive-units and small enclosure, the Alón PW1 really only qualifies as a woofer rather than a subwoofer. As can be seen from figs.1 & 2, its output starts to rollout below 42Hz, the region of the lowest note of the double bass or 4-string Fender bass. Fig.2 shows that it neatly fills in for an octave below the Petite, however, which has its 6dB-down point at a moderate 55Hz—not bad extension for such a small speaker. With an impedance dropping to just below 6 ohms (fig.3), the PW-1 won't present amplifiers with any drive problems, even when paralleled with the Petite (fig.4), which drops below 8 ohms only in the midrange.


Fig.1 Alón PW-1, nearfield woofer and port responses.


Fig.2 Alón PW-1 & Petite, complex sum of nearfield woofer and port responses.


Fig.3 Alón PW-1, electrical impedance (solid) and phase (dashed) (2 ohms/vertical div.).


Fig.4 Alón Petite, electrical impedance (solid) and phase (dashed) (2 ohms/vertical div.).

Carl Marchisotto mentioned to Bob Reina that reflex-loaded designs tend to ring more than an equivalent sealed enclosure. To illustrate this point, figs.5 & 6 show the individual step responses of the PW-1's two woofers and one of its four ?"-diameter ports, respectively. As expected, the woofer's output is in positive polarity and the port's negative, this typical of a reflex design. But note the significant ringing, extending out to the 100ms edge of each graph. In a sense, you have here an example of the Uncertainty Principle: The more narrowly you define a loudspeaker's passband in the frequency domain (and figs.1 & 2 show that the PW-1 covers a narrow passband of just an octave), the more indeterminate its output will be in the time domain. BJR mentioned the Trio's system as having a subjective boost in the 60Hz region; this will be associated with the ringing seen in figs.5 & 6 and the bandpass character seen in figs.1 & 2.


Fig.5 Alón PW-1 woofer, nearfield step response (100ms time window, 1kHz bandwidth).


Fig.6 Alón PW-1 port, nearfield step response (100ms time window, 1kHz bandwidth).

Overall, the measurements suggest a well-engineered stereo woofer given the compromises inevitable at the $500 price point. I can see why Bob (and WP) liked the PW-1 when they used it with the Alón Petite.—John Atkinson