Quote Originally Posted by Feanor View Post
The article linked by E-Stat asserts the fact of "accoustic gain" and links it to the area of the transducer. I'll admit I didn't understand how this wasn't "getting something for nothing", but I read the item only once so maybe it just when by a little too quickly.
The answer is mutual coupling. You may be aware of the retired engineer over at AA who is a big Advent proponent. I've had the good fortune of visiting him during a business trip. Here is his explanation. It is true that such is not a consistent 6 db gain across all frequencies.

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