An 'ideal' loudspeaker can be imagined, perhaps as some form of pulsating or vibrating sphere, neither of which is practicably realizable with precision if any reasonable power output is required. Suppose, however, we were to plot the air particle velocity components normal to a plane interposed between an imaginary ideal source and the observer. If we now substitute a plane surface with the same distributed velocity pattern, it follows (if the surface area is sufficiently large) that a replica of the curved wavefronts would be created and we would have an accurate acoustic 'picture' of our ideal source for any position of the observer. What is meant by sufficiently large? What happens if the area is restricted to practical dimensions? A new look at electrostatic loudspeakers shows that these problems can be solved and the concept capable of realization with a high degree of precision.
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