Keywords: Listening machine pic2.JPG An acoustic aircraft detection device used by the Dutch army in the Legermuseum Delft Before the development of radar acoustic horns like this were employed for air defense to listen for the engine sounds of incoming enemy aircraft It consists of two pairs of horn detectors connected by rubber tubes to stethoscope type earphones worn by a technician represented by mannikin The horizontal pair detected the horizontal position azimuth of the aircraft the vertical pair detected the vertical position elevation They were mounted on a gimbaled frame and could be scanned across the sky own 2010-01-17 12 58 48 AlfvanBeem CC-zero Legermuseum Delft Military related photographs by Alf van Beem Sound locators |