The acoustic lab’s anechoic chamber
is among the quietest places on Earth.
Definition: Anechoic | an-eCHO-ik | adjective.
Free from echoes and reverberations.
Purpose: For testing the sensitivity of microphones being developed to improve hearing aids.
Researcher: Ron Miles, distinguished professor of mechanical engineering and associate dean of research
Location: The chamber is isolated underground, 2½ feet beneath the floating cement pavers at the entrance of the Engineering and Science Building.
Inside: More than 600 fiberglass wedges absorb and minimize sound-wave reverberations down to 80 hertz. (Speech is between 500 and 5,000 hertz.) The floor is wire mesh (with wedges underneath), and a removable plank system allows tables and equipment to be moved in and out of the room.
Outside: The chamber is inside a sound-stopping shell, which is inside a lab, which is underground. Thick walls of concrete and layers of insulation help block vibrations and noise. Going into the chamber requires going through four sets of doors; the heaviest doors are 260 pounds each.
Bottom: The 250-square-foot chamber “floats” on nine 4x4-inch springs that serve as shock absorbers.
Top: A microphone positioning system that moves on five axes in the chamber can create 3-dimensional maps of sound fields. The maps show how sound radiates from complex noise sources and loudspeakers.