For anyone following this thread, I did ask Richard variation of this question. He posted his response to the “Ask Richard” section of the Vandersteen website:
Nicholas (1/13/17): Richard, I miss the regular updates to the "Ask Richard" section! It gave me a reason to visit the Vandersteen website early and often. BTW...really loving my Quatro CTs (John @ Audio Connection is awesome).. I've got a freakishly-flat listening position in-room response down to 24 Hz (falls off a bit at 20 Hz). I'm driving it with an Ayre AX-7e w/ factory installed filters. When I started typing this, I didn't really have a question (other than asking to bring back the "Ask Richard" section...but now that I think about it... Is it possible to quantify the potential performance improvement of an amplifier when the input signal is attenuated by a first-order crossover -3dB @ 100 Hz? Intuitively, the amp will have less current requirements into the load (based on the attenuated input signal below 100 Hz). What decisions did you make when designing the M7-HPA that would differ than someone designing a full-range amp (with respect to the input signal and load demand characteristics)? Glad to be part of the Vandersteen family. - Nicholas Renter
HELLO NICHOLAS, THE FAQ IS STILL VERY MUCH IN PLAY BUT WITH SO MANY ARCHIVED NOT MANY QUESTIONS ARE NEW SO I DON’T ANSWER QUESTIONS WHICH ALREADY HAVE BEEN ANSWERED (NOT DUTCH EFFICIENT). IT IS HARD TO QUANTIFY THE IMPROVEMENTS HEARD WHEN THE POWER SUPPLY IS HELPED BY A HIGH-PASS AT 100Hz. YOUR DEALER COULD DEMONSTRATE IT TO YOU BY INSERTING THE HIGH-PASS AND THEN REMOVING IT. IT IS SUBSTANTIAL BUT LIMITED BY HELPING THE POWER SUPPY ONLY. THE M7-HPA IS A VERY DIFFERENT STORY AND ITS ADVANTAGES ARE HUGE BECAUSE THE CIRCUIT AND POWER SUPPLY ARE OPTIMIZED FOR HIGH-PASS ONLY. MANY FEATURES HAVE BEEN INCLUDED WHICH COULD NOT BE IF THE AMPLIFIER WERE TO BE FULL-RANGE. I WILL GIVE YOU ONE EXAMPLE TO HOLD YOU UNTIL WE GET THE WHITE PAPER. A FULL-RANGE AMPLIFIER HAS TO HAVE MULTIPLE OUTPUT DEVICES IN ORDER TO HANDLE THE CURRENT NEEDED FOR THE WOOFERS. MULTIPLE OUTPUT DEVICES (TUBE OR SOLID STATE) SMEAR EACH OTHER SLIGHTLY BECAUSE THEY CANNOT BE EXACTLY THE SAME. IN THE M7-HPA VERY FEW OUTPUT DEVICES ARE NEEDED AND NO EMITTER RESISTORS ARE USED CAUSING NOTICABLE IMPROVEMENT IN DYNAMICS AND TRANSPARENCY.