NATIONAL PHYSICAL LABORATORY (C) CROWN COPYRIGHT / SCIENCE PHOTO LIBRARY NATIONAL PHYSICAL LABORATORY (C) CROWN COPYRIGHT / SCIENCE PHOTO LIBRARY
Testing an audio system. The thresholds of loudness and high frequency are being tested by projecting progressive plane sound waves at a listener. Progressive plane waves travel from one location to another as a series of parallel waves, allowing some sounds to be clearly heard from a distance. Photographed at the National Physical Laboratory, Teddington, UK, in 1954.
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