Snell Acoustics hosted a Q&A seminar as chaired by Dr. Joseph D’Appolito, who is infamous for his “D’Appolito Configuration” that has been adopted by many loudspeaker companies. In 2003, the good doctor, having created highly visible products for Usher Audio, joined Snell Acoustics, and in 2007 the $60,000/pair Illusion Reference Tower loudspeaker system was born. This AKFEST saw the launch of the $20,000/pair Phantom Tower, the lower model to the Illusion (Coverage II & Coverage III).
The following is an excerpt from the Snell Illusion Whitepaper that illustrates the design philosophy behind the Illusion, and the MTM array of the “D”Appolito Configuration” that has been adopted by many other speaker companies:
“The Configuration”
What was fixed from the beginning was the basic configuration. The Illusion was to be a 3-way loudspeaker. It is our strong belief that the critical midrange and its lower overtones should be reproduced in a single driver or driver pair. In the Illusion this is the frequency range between 250Hz and 2500Hz. This is also the frequency range of maximum human hearing acuity. A single driver will provide excellent coherence with no spatial ambiguity. By contrast, a 4-way system will invariably involve transitioning from a lower frequency midrange driver to an upper frequency midrange driver. Typical crossover frequencies are in the range of 600Hz to 800Hz. It is extremely difficult to make a seamless crossover in this frequency range. Furthermore, the quality of the midrange drivers in the Illusion makes such a crossover unnecessary.
Also fixed form the start was the use of our signature MTM driver array to reproduce all frequencies above 250Hz. This array comprises a pair of midrange drivers, one above and one below a central tweeter. This arrangement of drivers, popularly known as the “D’Appolito Configuration”, was developed by our Chief Engineer, Dr. Joseph D’Appolito in the early 80’s. Over the past 20 years countless loudspeakers produced with vertical mid-high-mid driver layouts have claimed D’Appolito status without any particular technical (or legal) legitimacy. A true D’Appolito array is a far more sophisticated entity, whose transducer parameters and dimensions, geometric relationships, and time-domain characteristics of crossover-filter circuits must all be meticulously calibrated to produce the intended result.”
Dr. Appolito authored a new book titled Testing Loudspeakers (Audio Amateur Press) recently, and attendees of this AKFEST were privy to what he had instilled into the pages of his literary work. Per Bob Graffy, Vice President and Brand Manager of Snell, Dr. D’Appolito gave his presentation to a roomful of 80 attendees, turning away another 50 attendees or so. The following is a collection of pictures I took of the slide show for your viewing pleasure. Please note that the following represents only the first half of the presented slides at the show.
Also among attendees were other loudspeaker designers who put forth very specific technical questions, such as placements of crossover, baffle design issues, etc. As typical of highly knowledgeable master designers, open-ended and even irrelevant questions opened up the doctor’s creativity and insights were poured out of him. One of the more interesting question raised by the audience was, “If different reviewers all have different preferences, what are we to make of their finding?”
Only as a subjective research paper that will serve to get you to your local dealer near you for a test drive. Some of us reviewers take our jobs so overly serious, that they treat their own words as if they were sacred. We should know better and treat reviews like an inspirational read. Don’t go “this reviewer said it is no good, and that reviewer also gave it a thumb down.” Trust your own ears and see if you agree with the review. Only when a significant enough mass of audiophiles begin to demonstrate their confidence in their own ears, can this audiophile hobby be truly fun and not as cut-throat as it has sometimes turned out to be. It is very sensible for you to be bent on acquiring a CD player because you heard it and couldn’t get over it, but it is not right to restrict yourself to all but that one or two pieces labeled as the “best” by the audio press. The audio industry is like a field of flowers and the consumers bees. Have fun at it, learn from each other and we all will thrive.
Toward that attendee’s question, Dr. D’Appolito offered no definitive answer, which is appropriate. Because while the most that the audio press can do is to suggest what to explore, who can tell the enquirer what he should or should not like but the enquirer himself?
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