Listeners adapt within minutes to externalize sound even through crude transducer devices

Evidence

One of the most unexpected experiences occurred in the NRCC lab, where ear defenders had been developed and there was a continuing interest. Acos, a British company known for its crystal microphones, had created a clever device called the Erdefender (in the 1970s, as I recall). It consisted of a hard-shell ear defender for each ear with 1-inch crystal microphones on the outside of each aimed at 90° left and right to the sides. Under each shell was a small loudspeaker, and in the headband was an amplifier that transmitted the microphone signals to the respective ears. It was intended to be worn by workers in noisy environments, and it would allow normal communication with the outside world but limited the maximum sound level inside the hard shell to protect hearing. … Considering what was known about binaural hearing, it was a very crude device. Dr. Edgar Shaw was involved with the evaluation, and he was then in the process of explaining the physical acoustics of the external ears—pioneering research predating HRTFs (e.g. Shaw, 1966, 1974). Our expectations were not high for any “fidelity” in the experience, focusing on the hearing protection aspect. The sound quality was poor, the result of inexpensive directional microphones, questionable loudspeakers, and unknown signal processing. But we were surprised to find that after only a few minutes of adaptation we all experienced externalization of the perceived images. — Toole, Floyd E, Sound reproduction- the acoustics and…, 298

Categorization

• XREF: Echoes the adaptation mechanism in the Sennheiser anecdote (296) and reinforces that neural plasticity, not transducer fidelity, drives externalization.
• SEED: An essay angle on how hearing-protection hardware inadvertently reproduced convincing binaural spatial cues, hinting that minimal cue fidelity plus adaptation suffices for externalization.