Tip #66 (February 2009)
BassZilla Platinum Mk2: A New Tweeter Alternative

by Dick Olsher

One of the most common questions to come my way has to do with driver substitutions. My standard response is to discourage substitutions because they generally require a redesign of the associated crossovers, and in the case of the woofer, a retuning of the enclosure. Well, occasionally there is an exception to the rule. A recent inquiry by RS of Hawaii raised the possibility of substituting the Aurum Cantus G2 tweeter, the G2Si’s larger (and more expensive) sibling. The parameters of the G2 were sufficiently similar to those of the G2Si that it appeared likely that it would require little tuning for use in the Platinum Edition Mk2. The potential payoff, of course, was a smoother response and slightly more output in the extreme treble.

The good news is that G2 works beautifully as a direct substitution for the G2Si without any changes to the crossover network. The Figure below shows the in-room frequency response of both versions of the Platinum Mk2, measured at about 49 inches on the tweeter axis. The green trace is for the G2 version. The increased output above 7 kHz is clearly visible. And yes, it sounds as sweet and even more detailed relative to the G2Si.
Mk2 Platinum mad-XO G2-G2Si tw axis2
For the record, my samples of the AC-G2S with round faceplate were obtained from E-speakers.com. The baffle cutout (see below) for the G2 is similar to that of the G2Si, the only difference being the increased height of the cutout (88 mm vs. 80 mm). Be sure to rabbet in the tweeter as well as the fullrange to maintain the acoustic centers of the drivers within their design limits.