"It will be seen that the mechanical reactance caused by the air chamber behind the cone is three times the mechanical reactance resulting from the suspension system. Therefore, in the range where the compliances are the controlling mechanical reactances the compliance caused by the air chamber is the controlling compliance. (Hence a high alpha or Acoustic Suspension system). This expedient reduces the distortion caused by a nonlinearity of the suspension system."
From the RCA patent. Comment within brackets is from me.
Of course, I don't expect contradictory facts to change your opinion in the least,
In the nearly sixty years since Villchur (Villchur -- two els) introduced the acoustic-suspension speaker, there have been dozens (perhaps hundreds) of critics and naysayers -- usually retired-speaker designers -- trying to discredit his accomplishment of the acoustic-suspension loudspeaker. You should feel honored that you are not the first to say that Olson and Preston anticipated the acoustic-suspension system! But as is usually the case, most of these criticisms are oversimplifications (a good example IMO is your statement above, "hence a high alpha or Acoustic Suspension system") and eventually fade away.
The problem with Edgar Villchur's patent was that he wrote the patent himself, and he didn't use a patent attorney because he couldn't afford one. He therefore didn't do due diligence in performing an adequate patent search. Villchur's patent could easily have been written in such a way as to protect itself against "prior art," had there been adequate patent research. As it happened, Olson and Preston's patent (#2490466) was missed by Villchur and his patent examiner during his search.
Villchur has said that shortly after AR was established in 1954 to build acoustic-suspension speaker systems, there were two licensees, KLH the Heath Company. It wasn't long before articles began to appear attacking the validity of the air-suspension design, and in one article ("Design of a Wide-Range Ultra-Compact Regal Speaker System") the authors -- engineers from Electro-Voice, Avedon, Kooy and Burchfield -- wrote:
"…On almost every point of performance the small cabinet is at a disadvantage … when it is said air suspensions are inherently more linear than mechanical suspensions a misstatement has been made…." This article went on to say that the non-linearity of the air was "an unavoidable consequence of the laws of physics."
In this same article criticizing the "non linearity of air," these engineers also described an air-suspension system that E-V had just introduced. When AR found out about this development, the company sued E-V for infringement of the patent, and the E-V attorney produced the RCA patent (that had been filed by Olson and Preston several years earlier) as anticipating the acoustic-suspension patent. The Olson-Preston claim was for a compliant-suspension speaker, but there was no claim for a system that had a free-air resonance below the optimum frequency, as with Villchur's invention. This is the characteristic of the acoustic-suspension system -- actually requiring a small enclosure. The essential proposal of the RCA patent was to improve speaker bass performance, in distortion and frequency response, by extending the region of mass control downward in frequency. Olson and Preston accomplished this by means of a compliant, folded-rim suspension that lowered the speaker's fundamental resonance frequency and allowed large, linear voice-coil travel. Olson and Preston plotted the reduced distortion for their speaker only for infinite-baffle mounting, and they showed optimum frequency response for the same mounting. They also pointed out that if their speaker were mounted in a small, enclosed cabinet, the resonance frequency could be raised to a point that was "still desirably low," and they showed a frequency response for such a mounting -- much inferior to that with the infinite baffle in low-frequency range and in correct value of Q, but superior to results with an open-back cabinet.
Where Villchur's air-suspension design relied on a cushion of air behind it, the Olson and Preston design was shown as being better off without the cushion of air, but capable of tolerating it for non-high-fidelity applications. There was therefore never a question of Villchur's speaker infringing on the RCA patent -- since the latter made no general claim for a low-resonance speaker in a small cabinet. However, the court in South Bend, Indiana ruled that Villchur's patent had been "anticipated" by the RCA patent. Because of a likely protracted legal fight -- and in view of what happened in 1954 (suicide) to Edwin Armstrong, the father of FM radio after his protracted fight (also) with RCA -- Villchur decided not to appeal the decision. The feeling was that AR could prevail, but it was not worth the tribulation to do it.
David, I am sure you've read Frederick V Hunt's Electroacoustics. My favorite quote is on page 87, in which Dr. Hunt states:
"As is often the case with ideas that appear superficially to be simple, a good many loudspeaker designers discovered that they had already made this invention -- after someone else had pointed out what the invention was. For example, there is a tendency to label as a forerunner of the base-reflex principle any prior-art loudspeaker in which an incidental hole or side opening in the cabinet can be identified. The primitive disclosures of Finch (Pat No. 216840) and Colby (Pat No. 371551) are of this sort. Merrill and Hays (Pat No. 669944) went a little further by exhibiting an enclosure containing holes intended to 'prevent the formation of a dead-air cushion against a receiver diaphragm.'"
This seems to sum it up pretty well.