Buildings located near airports may be subjected to significant noise levels. Aircraft noise is particularly annoying when compared to other traffic noises due to its periodic nature. Automobile traffic is a more consistent noise source, thus is more likely to be filtered out over time; however, aircraft noise exhibits a more cyclical nature thus is harder to filter out as “background noise.”
While noise control is typically performed at the source, sound insulation programs are part of the balanced approach in place to help mitigate noise at the receiver. Noise Level Reduction (NLR) is a common metric used in the US to determine whether a residence qualifies for such programs. Sound insulation Programs are available to houses that haven indoor Day Night Average Sound Level (DNL) 45 dB. NLR is a single-number metric used to quantify the ability for a building or building element to reduce the transmission of external sound pressure levels generated by aircrafts. In addition to determining whether a residence qualifies, NLR can be used to quantify the effectiveness to the modifications performed as a result of the sound insulation program. NLR measurements with a loudspeaker offer an alternative to those performed with aircraft flyovers. A loudspeaker offers flexibility to the consultants that perform these measurements in the field.
The purpose of this research was to better understand and improve the loudspeaker method for measuring NLR. Testing was completed on a "test house" that was constructed on campus with construction methods typical of a mixed-humid climate. The angular dependency, repeatability, and reproducibility of NLR, among other factors, were evaluated with field measurements. Significant NLR variations were observed with changes in lateral and vertical angles of incidence. The overall goal of the project is to improve the loudspeaker method of NLR testing, providing a resource to the aircraft noise industry.