Ear trumpet bells need to match wavelength to capture low-frequency sound

Evidence

A large ear trumpet would help enhance lower frequency sound. The reason is seen from the reciprocity law: low-frequency sound originating at the throat is reflected at the mouth if its wavelength approaches the size of the bell. It doesn’t escape well, nor, by reciprocity, does it enter well. — Eric J. Heller, Why You Hear What You Hear- An…, 596

Categorization

• QUESTION: Why wouldn’t a few large trumpets placed in a venue serve as passive low-frequency amplifiers? Worth chasing how reciprocity constrains such devices.