ANDREW BROOKES, NATIONAL PHYSICAL LABORATORY / SCIENCE PHOTO LIBRARY ANDREW BROOKES, NATIONAL PHYSICAL LABORATORY / SCIENCE PHOTO LIBRARY
Acoustic duct. Researcher looking down an acoustic duct, which is used to calibrate microphones and sound level meters. The duct is nine metres long with a rockwool insulator at one end and a loudspeaker at the other. Typically, measurements can be performed over the frequency range from 31.5Hz (hertz) to 250Hz. Photographed at the National Physical Laboratory in Teddington, UK.
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