Research Projects

Standardizing Aircraft Noise Reduction Measurements for Airport Sound Insulation Programs

Current research by FAA regarding outdoor-to-indoor sound insulation measurement best practices for airport noise mitigation programs is anticipated to conclude during 2020, but will not address supplemental measurement methods or standardization of data analysis and documentation processes. The need for further investigation in these areas was highlighted by earlier ACRP-sponsored research and is necessary to attain comprehensive standardization and consistency of aircraft noise reduction measurements on a national level.

Background (Describe the current situation or problem in the industry, and how your idea would address it.)

This idea is by Eric Cox, HMMH and Ben Sharp, Ben Sharp Acoustics.

The most common approach currently used to conduct aircraft noise reduction measurements of residential buildings for airport sound insulation programs is to adapt the American Society for Testing and Materials (ASTM) E966-10 procedure, which incorporates an outdoor amplified loudspeaker and exterior and interior sound level measurements. The ASTM E966-10 standard provides general guidance, but lacks options for conducting measurements in realistic situations regularly encountered in the field. Therefore, FAA is sponsoring ongoing research regarding outdoor-to-indoor sound insulation testing best practices for airport noise mitigation programs. This work is anticipated to conclude during 2020 and result in the development of a new Society of Automotive Engineers (SAE) International standard for conducting outdoor-to-indoor aircraft noise reduction measurements.

Previous ACRP-sponsored research highlighted the need for further investigation into the feasibility of using an indoor-to-outdoor testing method (loudspeaker placed inside the home) as a supplemental or alternative measurement approach and recommended development of a process for determining the representative exterior aircraft noise spectrum to use when calculating noise level reduction test results.

Indoor-to-Outdoor Measurements:

The ASTM E966-10 test procedure and forthcoming SAE International sound insulation standard both require the application of adjustment factors to the exterior noise level measurement results to account for the reflection of sound energy from the building façade surface, and also include specifications for loudspeaker placement which can be difficult to satisfy given realistic field conditions such as limited yard area or closely spaced houses.

An alternative method of conducting sound insulation testing with an artificial source is to place the loudspeaker inside the home and measure the noise reduction from inside to outside, thus eliminating the need for any adjustments to the test data. The interior sound level is obtained using a 3-D spatial scan over the room volume and the exterior sound level is measured using a 2-D scan over the room façade. The difference between the interior and exterior average sound levels is then a measure of the indoor-to-outdoor noise reduction that is in theory equivalent to the outdoor-to-indoor noise reduction result that would be measured using the new SAE International testing standard. The indoor-to-outdoor method also has the advantage that the contribution to the overall façade aircraft noise reduction from different building elements (i.e. windows, doors, etc.) can be directly measured. Moreover, an interior loudspeaker placement would eliminate noise complaints from nearby residents during the testing.

The proposed research would investigate the viability of using an indoor-to-outdoor acoustical testing method as a supplemental or alternative approach for conducting noise reduction measurements of residential building facades for airport sound insulation programs. The objectives of the research study would be to determine feasibility and preliminary best practices for conducting the indoor-to-outdoor noise reduction measurements and to demonstrate equivalence with the outdoor-to-indoor method given adherence to the testing procedures and data analysis parameters developed through this work.

Aircraft Noise Spectrum Utility:

Aircraft noise level reduction calculations are dependent on both the measured sound transmission loss characteristics of the residential structure and the frequency content of the exterior sound spectrum. Therefore, the aircraft noise spectrum used in the data analysis process is an important consideration in the accuracy of estimating residential building façade noise level reduction.

Airport sound insulation program sponsors currently utilize a variety of different methods to determine representative aircraft frequency spectra since there is not a guidance document or industry standard to reference. The proposed research will develop a process for selecting a representative aircraft spectrum for use in calculations of noise level reduction which can be standardized and streamlined. The research will develop a spreadsheet tool or software utility incorporating data such as annual aircraft operations, reference Sound Exposure Levels (SEL) for each aircraft type, and runway use information to calculate representative exterior aircraft spectra specific to an individual airport and adjacent community.

National Sound Insulation Database:

Information and results from residential sound insulation measurements conducted for airport noise mitigation programs are individually reported to FAA by program sponsors as part of the AIP federal grant process. The research project proposes to compile this data into a coherent publicly-available nationwide database to enhance the utility of this information to airports for various analyses, such as evaluating variations in aircraft noise reduction for different geographic regions, land uses, construction types, or aircraft noise exposure levels. In addition to populating the database with an example set of information, the proposed research would establish procedures and processes related to logistics and development of a national database in advance of the release of a new SAE International testing standard to ensure timely collection of measurement data when available.

The sound insulation testing standard currently being developed through FAA-sponsored research is likely to require evaluation of factors such as building shielding, interior absorption, or other detailed information which were generally not included in older data sets, as well as revisions to methodologies for testing of corner and other multi-façade rooms. Therefore, including historical information in a new national database is not recommended until all sound insulation measurements are conducted following the SAE International testing standard under development to confirm completeness and consistency.

Objective (What is the desired product or result that will help the airport industry?)

he proposed research has three objectives: 1) Investigate best practices for conducting indoor-to-outdoor noise reduction measurements of residential building facades as a supplemental or alternative option to the more common outdoor-to-indoor measurement method, 2) Develop a utility to compute representative A-weighted aircraft spectra for use in calculations of noise level reduction and 3) Establish procedures and processes for the development of a national sound insulation database.

Cost Estimate and Backup (Provide a cost estimate and support for how you arrived at the estimate.)

18 months, $500k

Related Research - List related ACRP and other industry research; describe gaps (see link to Research Roadmaps above), and describe how your idea would address these gaps. This is a critical element of a synthesis topic submission.

Sharp, B.H., Cox, J.E., and Zheng, Z.C. (2019). "NLR Measurement Method Equalization and Normalization", DOT/FAA/TC-xx/xx, March 2019.
Sharp, B.H., Cox, J.E., and Zheng, Z.C. (2017). "Investigation of ASTM E966 Adjustment Factors", DOT/FAA/TC-18/15, April 2018.
Bajdek, C.J., Cox, J.E., Mentzer, R.C., Nicholas, B.L., and Reindel, E.M (2016). "Review and Evaluation of Aircraft Noise Spectra used to Estimate Noise Level Reduction for Airport Sound Insulation Programs based on the Loudspeaker Test Method", HMMH Report No. 305220.008 prepared for the Federal Aviation Administration, February 2016.
Schomer, P., Freytag, J., and Waldeck, R. (2016). "Evaluating Methods for Determining Interior Noise Levels Used in Airport Sound Insulation Programs", ACRP Report 152 prepared for the Transportation Research Board, Airport Cooperative Research Program (ACRP), Washington, DC, 2016.
Sharp, B.H. and Martin, S. "The Measurement of Aircraft Noise Reduction in Residences", Proceedings of InterNoise 96, p803, Liverpool, 1996.

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Idea No. 186