E-A-R Thermal Acoustics Systems (Stand 2145) is improving acoustic insulation aboard business jets as it endeavors to cut the most annoying cabin noises on a case-by-case basis.
Overall, the best the aviation industry has done so far is focus on the speech interference level (SIL). Manufacturers normally present sound pressure levels, measured in dB at SIL, to indicate how quiet their cabins are. These levels currently are 50 percent lower than they were 10 years ago. However, the dB SIL level in the cabin does not necessarily measure actual acoustic comfort, Brian Joyal, E-A-R’s director of aerospace, defense and rail business, told AIN.
“We are making sound quality better in the cabin by looking at the frequency content of the noise spectrum; it is more than just reducing an overall noise level measured in dBs,” Joyal said.
The noise spectrum is a combination of all noise sources emanating from and around the aircraft. The boundary layer (the air flow on the aircraft’s surface) has a broadband frequency content, while the engines and aircraft systems (fuel and hydraulic pumps, for instance) have rather discrete harmonics. Some actuators also produce discrete harmonics, the noise from which is considered especially annoying. “The frequency content of the noise spectrum is the key to understanding the cabin’s sound quality,” Joyal said.
E-A-R maps the acoustic power flow in the aircraft, and then chooses the right insulation material for the right place. For example, some areas receive structural damping treatment, while other materials act as reflectors of airborne acoustic energy. The U.S. company also has designed mufflers for the air-pressurization system. “Treating noise contributions on a discrete basis helps minimize weight,” he added.
But is good acoustic insulation also good for thermal insulation? “Not necessarily, as acoustic insulation involves a certain amount of air flow, while thermal insulation should be more closed,” Joyal said. Noise insulation is more challenging than thermal insulation, and the company has developed composite blankets with different layers to address these different goals.
The Indianapolis, Indiana-based company’s customers include business jet manufacturers and companies specializing in VIP cabin outfitting, such as Comlux, Amac Aerospace and Lufthansa Technik.