Hi Ozzy,
I took a look at the photos in your system description thread, and also at the very comprehensive technical info provided at the Aurum Cantus site
My first comment is that it looks like you’ve done an extremely impressive job of assembling a very sophisticated system!
It appears that your G1 ribbon tweeter and whichever of the Aurum Cantus mid-woofers you are using have benign impedance characteristics, which don’t descend significantly below their 8 ohm nominal ratings at any frequency, and don’t have highly capacitive phase angles outside of the deep bass region (in the case of the mid-woofers) which they won’t be handling anyway. Also, it looks like the external crossover you’ve built consists of second order LC filters (low pass for the mid-woofer and high pass for the tweeter, of course), with a resistive pot in the high pass section to pad down the tweeter’s sensitivity to match the mid-woofer’s. I don’t see any of that as presenting any problem for the M-60, used without Zeros.
Also, while most of the energy that is contained in most music most of the time will be present at frequencies that will be handled by these drivers, as opposed to the subs (my understanding is that 350 Hz represents a rough rule of thumb for the frequency at which most music most of the time has equal amounts of energy above and below), the 60 watt capability of the M-60 into 8 ohms should get you to peak volume levels in the area of 101 to 104 db or so at a 10 foot listening distance, with a 90 db speaker that can handle that amount of power without significant thermal compression (as appears to be the case here).
Some further points:
While I’m not totally certain, I think it might be worthwhile to re-do the DEQX speaker calibrations once the new amp is in place. I’m envisioning that the interaction between the amp’s 4.1 ohm output impedance and the characteristics of the cross-over/speaker combination might change the results you obtained with the Pass amp, and its near zero output impedance. Although I’m not certain of that, as I said. Fortunately your DIY speakers are not multi-hundred pound monsters, and should be fairly easy to move, if that is necessary to minimize room reflections during that procedure.
Second, keep in mind that the interaction between the 4.1 ohm output impedance of the amp and the 8 ohm speaker impedance will reduce gain by a few db, relative to what you have with the Pass amp, and will require a corresponding rebalancing of the speakers with the subs.
Finally, I note that the frequency response plots for the Aurum Cantus drivers show some significant variations within the frequency ranges they will be handling, such as a rise of more than 5 db in the response of the tweeter in the top octave, and significant rises in the upper mid-range/lower treble responses of many of their mid-woofers. The DEQX should be very helpful in providing whatever corrections may be needed for those variations.
Best of luck. Regards,
-- Al
