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Improved Method for Estimating Noise Level Reduction of Residential Houses
Abstract
To mitigate noise impact to residents around airports in the US, the Federal Aviation Administration has a Residential Sound Insulation Program. An aspect of this program is the estimation of the building Noise Level Reduction. A commonly used method of measuring Noise Level Reduction uses a loudspeaker outside the house and microphones inside. This measurement technique has a few limitations such as likely noise disturbance to neighbors, effects of flanking path and interfering noise , and inability to identify the sound isolation weaknesses of the house. Two changes are proposed. First, disturbance is reduced by moving the loudspeaker inside the house and measuring the sound outside. Reciprocity ensures that the result will not change, in principle. Second, a microphone phased array outside the house and a state of the art processing method, Robust Adaptive Functional Beamforming, are used to improve the dynamic range of the method and to pinpoint the acoustic leakage paths of the house. A preliminary test was conducted using a two-bedroom house at a university research center. The expected benefits were observed.
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There is an extensive body of theory, and some laboratory measurements, of sound propagation over a surface of finite impedance. There are also reliable measurements of outdoor sound propagation in near‐horizontal directions over the ground. In an attempt to relate these more closely, we have made carefully controlled measurements at ranges from 1 to 1000 ft, in most cases over grass‐covered flat surfaces, to demonstrate the several phenomena that are involved. These phenomena depend on, and conversely provide a means of estimating, the values of ground impedance for waves at near‐grazing angles of incidence. Such values obtained for grass‐covered surfaces are in reasonable agreement with each other and with values obtained by conventional means at other angles of incidence. It is suggested that simple but accurate predictions of noise levels can be made by assuming that an excess attenuation due to finite ground impedance would always exist in a certain shadow region near the ground. This shadow region is however penetrated at low frequencies by a ground wave, to an extent that depends principally on distance and ground impedance, and at higher frequencies by interference between direct and ground‐reflected waves to an extent that depends also on source and receiver heights. These phenomena, well established at ranges up to about 1000 ft and in some aspects to over 3000 ft, have been extrapolated theoretically to the order of 10 000 ft so that simple effects of topography and meteorology can be added to show how reflection or refraction acts in conjunction with ground impedance to result in penetration of the shadow region.
Subject Classification: [43]28.40; [43]20.55.
Functional Beamforming is a new method that promises to replace Frequency Domain Beamforming as the standard microphone array processing technique in aeroacoustics. It offers the same speed as FDBF with dramatically improved dynamic range and slightly improved resolution. It is not a deconvolution technique and is not compatible with standard deconvolution methods such as DAMAS because it is nonlinear. Unlike deconvolution, it renders smooth source distributions as smooth images. It can be extended to support integration for component source modeling by changing the normalization of the map. Its resolution can be improved by applying topological ridge detection to segment the beamform map and optionally by applying the Linear Programming deconvolution method to the reduced set of grid points in the segmented map.
Aviation Noise Transmission Indoors-Overview of FAA Research and Assessment of Future Research Needs
- H He
H. He, "Aviation Noise Transmission Indoors-Overview of FAA Research and Assessment
of Future Research Needs," NOISE-CON, Fort Lauderdale, Florida (2014)
Façade Sound Insulation Testing Using Aircraft and Loudspeaker Techniques
- Y A Gurovich
- G Ehrlich
Y.A. Gurovich and G. Ehrlich, "Façade Sound Insulation Testing Using Aircraft and
Loudspeaker Techniques", InterNoise The 33rd International Congress and Exposition on
Noise Control Engineering (2004)
Functional Beamforming
- R P Dougherty
R.P. Dougherty, "Functional Beamforming", Berlin Beamforming Conference, BeBeC 2011,
(2014)