Acoustic listening device.

Acoustic listening device.



Comments

  1. I'm certainly glad that hearing aids have gotten smaller over the years:)

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  2. I found out that these were actually early warning devices used in the war before radar was used. It enhanced the listeners ability to detect incoming airplane engines.

    I didn't say 'before it was invented' above because I understand it was offered to the war department and could have avoided Pearl harbor if it had been used. The war department drug its feet and wanted to think about the invention.

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