PB12-Plus/2 Measurements and Analysis (cont.)

Figure 8: PB12-Plus/2 impedance curves, taken with & without baseplate in place.

In Figure 8 we can see that the affect is minimal; with the baseplate in place the system tuning frequency shifts only slightly downward, which was anticipated.

Impedance curves are also useful in determining current draw (both magnitude & phase) for a system. The PB12-Plus/2 exhibited the current curves showing in Figure 9 Scaling the drive level upward, measuring the resulting z curve at each step and deriving the current curves can give a pretty comprehensive picture of what the system will demand of the amplifier driving it.

Figure 9: PB12-Plus/2 current draw, in Amperes, at 16, 20 & 25 Hz system tunings.

The PB12-Plus/2 comes with a useful array of features built in to the power amp. The variable electronic crossover provides for a lowpass crossover function, useful for setting up your sub to integrate correctly with the rest of your system. Figure 10 shows the system response at a crossover setting of 120, 80, 60 and 40 Hz.

Figure 10: Electronic lowpass filter; fc = 120, 80, 60, and 40 Hz, measured nearfield, scaled to 1m, 2.828 Vac drive level.

Along with the electronic lowpass crossover, the PB12-Plus/2 sports an equally useful parametric equalizer. Figure 11 shows the results of a quick check of the variable Q function and Figure 12, the variable frequency function. I found both features indispensable in setting up the sub for proper room/system integration.

Figure 11: Parametric EQ, variable Q function, 2.828Vac drive level, scaled to 1m.

Figure 12: Parametric EQ, variable frequency function, 2.828Vac drive level, scaled to 1m.

Both features worked exactly as they should and were invaluable in setting up the sub.

In figure 13 are the measured results of a putting the PEQ to use flattening a low-Q response peak, located just under 20 Hz. As can be seen, the peak was indeed substantially flattened. Subjectively, the qualitative difference was substantial.

The stepped frequency highpass (HP) filter (used in conjunction with the system's tunable duct array) serves to both define the PB12-Plus/2's response below the chosen system tuning frequency as well as protect the driver's from damage. The literature supplied with the PB12-Plus/2 emphasizes the importance of selecting the correct highpass frequency for each of the 3 possible tunings. Once you've been exposed to just how powerful a unit the PB12-Plus/2 is, its easy to imagine how sensible and necessary it is to ensure the correct HP frequency is chosen. Doing so ensures maximum performance and a long, productive lifespan.

Figure 13: ParaEQ application: Red curve (before), blue curve (after).