NCPA Anechoic Chamber Aids Military Research

The University of Mississippi campus is outstanding for excellence in many areas, including research.

It is home to the National Center for Physical Acoustics, a research facility that serves as an advocate for physical acoustics to many organizations and federal agencies, including the United States military.

One of the fascinating facilities at NCPA is a sonically isolated anechoic chamber, which can be described as a room floating within a room. This comes from the fact that the chamber is a room with very thick walls and internal dimensions of 12x12x8-feet which completely floats on springs within another larger room in the NCPA. The very thick walls of the chamber and the fact that it floats on springs isolate anything inside the chamber from outside noise and vibrations.

The NCPA’s anechoic chamber is lined with foam wedges to eliminate sound vibrations. Photo Courtesy of Ole Miss News

The inside walls of the chamber are covered with large foam wedges that absorb sound waves that hit them from any source within the room. In normal rooms, sound waves bounce around as they are reflected off of the various surfaces in the room. What we hear is a combination of the original sound plus a lot of these reflections (think of an echo in a cave). On these foam wedge surfaces, the majority of the sound is immediately absorbed, so everything you hear is slightly muffled because all the reflections and echoes are absent and all that you hear is the original sound. In fact, when you hear a balloon pop while inside the chamber, it sounds as if you have cotton in your ears.

Due to the complexity of accomplishing this level of isolation and sound absorption, anechoic chambers are expensive to build and prized possessions for any facility doing acoustics research. The NCPA actually also has a second anechoic chamber for jet noise research with a slightly different design. We are very fortunate to have either, much less both, of these on our campus.

Anechoic chambers are great for precisely measuring the noise that things emit. Examples that have been measured at NCPA go all the way from termites to jet engines. For example, the U.S. Navy is interested in ways to make their jet engines quieter because of the hearing damage incurred by sailors on aircraft carrier decks. The aero acoustics research group at NCPA developed a method to decrease jet engine noise by 1.5 decibels, which they measured and validated using the jet engine anechoic chamber.

This is just one example of the great accomplishments in research happening at Ole Miss.

Courtesy of Ole Miss News
By Christina Steube