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Suggested Citation:"Chapter 1 - Overview." National Academies of Sciences, Engineering, and Medicine. 2016. Evaluating Methods for Determining Interior Noise Levels Used in Airport Sound Insulation Programs. Washington, DC: The National Academies Press. doi: 10.17226/23473.
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Suggested Citation:"Chapter 1 - Overview." National Academies of Sciences, Engineering, and Medicine. 2016. Evaluating Methods for Determining Interior Noise Levels Used in Airport Sound Insulation Programs. Washington, DC: The National Academies Press. doi: 10.17226/23473.
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Suggested Citation:"Chapter 1 - Overview." National Academies of Sciences, Engineering, and Medicine. 2016. Evaluating Methods for Determining Interior Noise Levels Used in Airport Sound Insulation Programs. Washington, DC: The National Academies Press. doi: 10.17226/23473.
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Suggested Citation:"Chapter 1 - Overview." National Academies of Sciences, Engineering, and Medicine. 2016. Evaluating Methods for Determining Interior Noise Levels Used in Airport Sound Insulation Programs. Washington, DC: The National Academies Press. doi: 10.17226/23473.
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Suggested Citation:"Chapter 1 - Overview." National Academies of Sciences, Engineering, and Medicine. 2016. Evaluating Methods for Determining Interior Noise Levels Used in Airport Sound Insulation Programs. Washington, DC: The National Academies Press. doi: 10.17226/23473.
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Suggested Citation:"Chapter 1 - Overview." National Academies of Sciences, Engineering, and Medicine. 2016. Evaluating Methods for Determining Interior Noise Levels Used in Airport Sound Insulation Programs. Washington, DC: The National Academies Press. doi: 10.17226/23473.
×
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Suggested Citation:"Chapter 1 - Overview." National Academies of Sciences, Engineering, and Medicine. 2016. Evaluating Methods for Determining Interior Noise Levels Used in Airport Sound Insulation Programs. Washington, DC: The National Academies Press. doi: 10.17226/23473.
×
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Suggested Citation:"Chapter 1 - Overview." National Academies of Sciences, Engineering, and Medicine. 2016. Evaluating Methods for Determining Interior Noise Levels Used in Airport Sound Insulation Programs. Washington, DC: The National Academies Press. doi: 10.17226/23473.
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Suggested Citation:"Chapter 1 - Overview." National Academies of Sciences, Engineering, and Medicine. 2016. Evaluating Methods for Determining Interior Noise Levels Used in Airport Sound Insulation Programs. Washington, DC: The National Academies Press. doi: 10.17226/23473.
×
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Suggested Citation:"Chapter 1 - Overview." National Academies of Sciences, Engineering, and Medicine. 2016. Evaluating Methods for Determining Interior Noise Levels Used in Airport Sound Insulation Programs. Washington, DC: The National Academies Press. doi: 10.17226/23473.
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Suggested Citation:"Chapter 1 - Overview." National Academies of Sciences, Engineering, and Medicine. 2016. Evaluating Methods for Determining Interior Noise Levels Used in Airport Sound Insulation Programs. Washington, DC: The National Academies Press. doi: 10.17226/23473.
×
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Suggested Citation:"Chapter 1 - Overview." National Academies of Sciences, Engineering, and Medicine. 2016. Evaluating Methods for Determining Interior Noise Levels Used in Airport Sound Insulation Programs. Washington, DC: The National Academies Press. doi: 10.17226/23473.
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Suggested Citation:"Chapter 1 - Overview." National Academies of Sciences, Engineering, and Medicine. 2016. Evaluating Methods for Determining Interior Noise Levels Used in Airport Sound Insulation Programs. Washington, DC: The National Academies Press. doi: 10.17226/23473.
×
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Suggested Citation:"Chapter 1 - Overview." National Academies of Sciences, Engineering, and Medicine. 2016. Evaluating Methods for Determining Interior Noise Levels Used in Airport Sound Insulation Programs. Washington, DC: The National Academies Press. doi: 10.17226/23473.
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1 1.1 Purpose of Report The primary purposes of this report, ACRP Report 152: Evaluating Methods for Determining Interior Noise Levels Used in Airport Sound Insulation Programs, are to discuss and clarify acousti- cal testing issues associated with airport sound insulation programs administered by the Federal Aviation Administration (FAA) and to provide proposals for improvement. The first ACRP report related to sound insulation programs, ACRP Report 89: Guidelines for Airport Sound Insulation Pro- grams was published in 2013 (Payne et al. 2013) to describe and suggest procedures for conducting sound insulation programs. ACRP Report 89 addresses the major elements of a sound insula- tion program, including program development, community outreach, acoustical engineering, architectural treatments, historic structures, ventilation, green building initiatives, contracting, funding, and reporting. Much of the background information for this report comes (with some minor updating by the research team) from ACRP Report 89, and it remains a good source for more detail on sound insulation programs. Important elements of airport sound insulation programs are the pre- and post-construction acoustical measurements to quantify the noise level reduction (NLR) of the structures. The purpose of these measurements is to: • Determine the eligibility of the home for treatment, in accordance with recent FAA guide- lines stated in Program Guidance Letter (PGL) 12-09 (FAA 2012b) and FAA Order 5100.38D (FAA 2014). Order 5100.38D (the Airport Improvement Program Handbook) requires that structures potentially eligible for sound insulation [i.e., within the DNL/CNEL (day–night average noise level/community noise equivalent level) 65 decibels (dB) noise contour] be evaluated to determine whether interior noise levels are high enough to warrant sound insulation treatment. Structures already providing good sound insulation, reducing inte- rior DNL/CNEL noise exposure to 45 dB or less, are ineligible for treatment under the program. • Provide a quality control check ensuring that a minimum 5 dB NLR improvement is realized from sound insulation treatment. Currently, various sound insulation measurement procedures are employed by the many acous- tical consultants working on airport sound insulation programs. There are no standardized proce- dures for airport sound insulation program measurements, although certain American National Standards Institute (ANSI) standards are typically followed as closely as practical. Current prac- tices depend upon consultant capabilities and experience, noise measurement budgets, and logisti- cal constraints. Overall airport sound insulation programs oversight is typically provided by the local FAA Airport District Office (ADO), but these offices rarely address acoustical measurement techniques. C H A P T E R 1 Overview

2 Evaluating Methods for Determining Interior Noise Levels Used in Airport Sound Insulation Programs With a program typically providing $25,000 to $30,000 of retrofit treatments at no cost to the homeowner (whose home is affected by airport noise), the acoustical measurements take on added importance within the updated handbook (FAA Order 5100.38D: FAA 2014). Based on field measurements conducted at 10 homes near San Diego International Airport and nine homes near Boston Logan International Airport, this report assesses the accuracy and validity of various NLR measurement procedures currently employed in airport sound insula- tion programs. The field measurements consisted of alternative NLR measurement methods. The measurement results were compared, and various measurement errors and the typical mag- nitude of each were evaluated and documented. Measurement tolerances were proposed, and specific measurement procedures were identified as “best practices.” 1.2 Summary of Findings The measurement of NLR of rooms within a home is complex because it is affected primarily by instrument error, microphone location, sound source location, and ambient (or background) noise in both the source and receiver locations, and further by meteorological conditions between. Additionally, measurement results vary with the sound spectra of the aircraft produc- ing the external DNL noise environment, since sound attenuation varies at different frequencies and differs by various building constructions. 1.2.1 Measurement Methods and Findings In July 2014, a team of three acoustical consultants and four technicians conducted acoustical measurements for a week on 10 homes in noise impacted areas around San Diego International Airport (SAN). These measurements were made using the following test methods: • Aircraft flyover—for all 10 homes using stationary and moving microphones. • Exterior ground-level speaker—for all 10 homes. • Exterior elevated speaker—for five homes. • Interior speaker—for all 10 homes. • IBANA (Insulating Buildings Against Noise from Aircraft) calculation—for all 10 homes. • Spreadsheet populated with industry-standard façade transmission loss (TL) calculations— for all 10 homes. • Sound intensity—for the first five homes. This measurement program was then repeated for a week on nine homes in noise impacted areas around Boston Logan International Airport (BOS). This program was less successful than that for the SAN testing due to shifting runway use. However, additional information was obtained, which generally supported the greater database of information obtained at SAN. Following is a brief description of each measurement method, technique, and results. 1.2.1.1 Aircraft Flyover • Action: The research team conducted aircraft flyover measurements at 10 homes near SAN and at four homes near BOS. Flyover measurements consist of the placement of one sound level meter outside of the home and one to three sound level meters in each of the rooms under test. The meters concurrently measure aircraft flyovers and the difference in flyover noise level between exterior and interior is calculated. (See Figure 1-1.) • Findings: – Measurements need to be conducted in vacant homes, as occupant contamination easily occurs. – On average, the NLR measured using the flyover method is 0.4 dB higher than the overall average NLR.

Overview 3 – There are some rooms with results that are outliers and these findings are discussed in Section 4.1. – The mean and the median noise reduction should be computed, because comparing the results from the two statistics provides a check on the validity and stability of the NLR results. – A properly placed single microphone is adequate for most NLR measurements. 1.2.1.2 Ground-Level Exterior Loudspeaker • Action: The research team conducted ground-level loudspeaker measurements at 10 homes in San Diego. In Boston, the research team conducted measurements in nine homes. The mea- surements were taken in two rooms per home and were conducted by placing a loudspeaker outside of the room under test, generating a loud test signal (pink noise) and measuring at the exterior façade and inside of the room being tested. (See Figure 1-2.) • Findings: – The NLR measured using the ground-level exterior loudspeaker method is, on average, 1.4 dB lower than the overall average NLR. – There are some rooms with results that are outliers, which are discussed in Section 4.8. – On average, calculated NLR using the OITC (outdoor-indoor transmission class) spectrum was slightly lower (0.5 dB) than that of the flyover spectrum. – In general, the results varied little when the measurements were repeated. – Similar to the elevated loudspeaker, the NLR decreased by approximately 1 dB when the roof and walls were measured at the exterior. 1.2.1.3 Elevated Exterior Loudspeaker • Action: The research team conducted elevated exterior loudspeaker measurements in five homes in San Diego and five homes in Boston. Two rooms per home were measured. The elevated loudspeaker measurement is performed in a manner similar to the ground-level loudspeaker, except the loudspeaker is elevated above the building via a crane or bucket truck. (See Figure 1-3.) Figure 1-1. Flyover measurement picture.

4 Evaluating Methods for Determining Interior Noise Levels Used in Airport Sound Insulation Programs • Findings: – The NLR measured using the elevated-level exterior loudspeaker method is, on average, 0.5 dB lower than the overall average NLR. – There are some rooms with results that are outliers; Section 4.8 discusses this in detail. – On average, the calculated NLR using the OITC spectrum was slightly lower (0.3 dB) than that using the aircraft flyover spectrum. – With repeated measurements, noise reduction did not significantly change. – NLR decreased by 0.8 dB when the measurement included a microphone scan of the roof. Figure 1-2. Ground-level loudspeaker measurement picture. Figure 1-3. Elevated exterior loudspeaker picture.

Overview 5 1.2.1.4 Interior Loudspeaker • Action: The research team conducted interior loudspeaker measurements in 10 homes in San Diego. In Boston, the research team conducted interior loudspeaker measurements in nine homes. Measurements were taken in two rooms per home. Interior loudspeaker measure ments were conducted by placing the loudspeaker inside of the room under test, generating a test signal, and measuring both inside of the room (source) and at the exterior of the room (receive). • Findings: – The interior loudspeaker method yielded NLR values significantly higher than the other methods. Differences like this are frequently systematic; it appears a correction is needed to account for reverberant build-up in the source room. The research team applied a 5 dB correction to the measurement data for reverberant build-up; however, additional investi- gation is necessary to determine the appropriate correction for the type of measurement. – There are some rooms with results that are outliers. – On average, the calculated noise reduction using the OITC spectrum was slightly lower (0.9 dB) than that calculated using the flyover spectrum. – NLR varied by less than 1 dB when measurements were repeated. – NLR increased when the wall and roof were measured. This is opposite of what happened when the loudspeaker was located outside. 1.2.1.5 Acoustical Calculations • Action: The research team performed noise reduction calculations using two calculation models: IBANA and a spreadsheet populated with industry standard TL formulas. The calcu- lations require detailed information on building element sizes (e.g., window area) along with information on the construction of the building elements. An additional and generally small computation is also made for the acoustical absorption effects of the room interior. Calcula- tions are made using either IBANA computer program or individual consultant spreadsheet programs and TL files for building elements. • Findings: – Both calculation methods resulted in similar NLR values for most rooms. – Calculations typically provide similar results as the exterior loudspeaker or flyover test- ing; however, the accuracy of the calculation is dependent upon a comprehensive field survey. – Flanking paths (e.g., noise leaks) can easily be missed in the field survey and calculation, resulting in overstatement of NLR. – The acoustical calculations resulted in NLRs that were higher than the average NLR by 0.7 to 1.3 dB. 1.2.1.6 Air Infiltration • Action: The research team measured air infiltration values via a blower door test, and correlated the air infiltration value to measured noise reduction. • Findings: – There is no correlation between the air infiltration results from blower testing and the measured noise reduction. 1.2.1.7 Sound Intensity • Action: The research team conducted sound intensity measurements in five homes near the San Diego International Airport. Additional measurements were conducted at a residence in Champaign, IL. The research team took measurements from outdoor to indoor, as well as from indoor to outdoor.

6 Evaluating Methods for Determining Interior Noise Levels Used in Airport Sound Insulation Programs • Findings: – Classical acoustic theory presumes that TL is the same in both directions (i.e., a wall performs equally whether the source of noise is inside of a home or outside of a home). Through this study, the research team found this generally to be true. – The best strategy when conducting sound intensity measurements is to measure as close to the exterior wall as feasible. – Based on the research team’s experience with this measurement method, the technology and time required preclude the use of sound intensity for airport sound insulation pro- grams at this time. – There are a number of enhancements suggested to provide for better sound intensity results and possibly allow for the use of sound intensity for airport sound insulation programs in the future. Additional research is needed. – Sound intensity holds the promise of being an extremely effective method because the results are virtually independent of weather effects, the measurements are independent of resonance effects, there are no neighbor noise disruptions, and nearby reflectors are not a problem. 1.2.2 External Sound Spectra A significant factor that affects the measured noise reduction is the external sound spectra (i.e., the noise “signature” of aircraft overflights at a given airport). The external DNL frequency spectrum to be modeled (from the FAA Part 150 program Noise Exposure Map) is unknown since it is the annual energy average of all aircraft over a particular location, with the 10 dB night- time penalty (a single nighttime flyover is equal to 10 daytime flyovers of the same level), under all annual meteorological conditions; it can only be estimated. The spectra of louder aircraft should be biased on an energy basis; for instance, a single flyover at 90 dB should be averaged equally with 10 flyovers at 80 dB. Since the sound spectra cannot be addressed in the field measurements addressed in this report, the issue of external sound spectra is beyond the scope of this study. Additional research and investigation is suggested. 1.2.3 Relative and Absolute Measurement Two basic types of measurements are now required: 1. Relative measurements—Those measuring only the difference or change from a previous measurement. For the residential sound insulation program (RSIP), this is the NLR im- provement from pre- to post-construction. 2. Absolute measurements—Those measurements without reference to other measurements. For the RSIP’s, this requirement is restated in the PGL/FAA Order 5100.38D to measure the pre-construction NLR to determine eligibility for acoustic retrofit. Prior to PGL 12-09, industry practice concerning noise reduction measurements was princi- pally relative measurements rather than absolute measurements. Relative measurements assess the change in noise reduction performance, whereas absolute measurements assess the absolute interior DNL values. There are various sources of error or uncertainty with the different NLR test methods. These include the effects of measurement location, instrument error, meteorological conditions, air- craft flight operations and fleet mix, and background noise. All relative measurements will incur less uncertainty than absolute measurements. Rela- tive measurements may duplicate certain uncertainties, such as instrument error (by using the same instrument for pre- and post-construction measurements). Therefore, for example, if an

Overview 7 acoustical instrument had a +0.5 dB error, it would not affect a relative measurement because the +0.5 dB would be added to both measurements and the difference would not be affected. Using the same instrument for an absolute pre-program qualifying measurement would incur the +0.5 dB in interior DNL. Therefore, additional care and enhanced precision are necessary for the interior DNL measurements to reliably determine whether structures are eligible for sound insulation (i.e., interior noise levels are greater than 45 dB). 1.3 Acoustical Testing Matrix Table 1-1 identifies various situations and measurement elements to be considered when selecting a particular test method. This has been developed to assist in choosing the most effec- tive and efficient test method for NLR measurement in a particular situation. Each method has advantages and disadvantages in terms of both technical accuracy and reliability, and in field implementation and costs. In developing the matrix in terms of errors, all methods are assumed to yield similar results after correction factors are applied (see Note 1 of Table 1-1). Therefore, it was necessary to average results for each method applied to each room of each residence tested. The variation from the average is given in the “average NLR difference.” However, this average is necessarily influenced by all test methods evaluated, some of which must be less accurate and reliable than others. So a method yielding a result closest to the average of all methods is not necessarily the best, most accurate, or most reliable. The best method is a method that is logistically feasible, has the smallest average NLR differ- ence and standard deviation, and conforms to a national/international standard. 1.4 Acoustical Testing Decision Matrix Table 1-2 is a decision matrix addressing various situations and measurement elements to be considered when selecting a particular test method. This may be used to assist in choosing the most effective and efficient test method for NLR measurement in a particular situation. Each of the measurement issues listed may be reviewed with respect to any particular test program. This should assist in selecting the optimum test method for a particular program. For specific homes and measurement issues, it may be advisable to add to this list for a specific evaluation. Noise level reduction measurements are made (1) to assess eligibility for acoustical treatment according to PGL guidelines and (2) for quality control to determine the degree of NLR achieved from acoustical retrofit. The three main considerations in selecting a particular testing method are technical issues, administrative issues, and financial issues. There is no single method that is best for every home or program since physical, administrative, and financial issues vary with every program. The primary technical issues with the aircraft flyover method are the availability of aircraft types and flight tracks in the area to be measured on the day of measurement. The aircraft activ- ity measured should reasonably represent a sampling of the average annual aircraft operation from the Integrated Noise Model (INM)/Aviation Environment Design Tool (AEDT) qualifying the sound insulation program. Particular attention should be paid to nighttime operations, since they are biased by 10 dB in the DNL assessment. The ground-level loudspeaker measurement method may be constrained by second story homes where it is difficult to produce significant sound energy on the roof. This situation is particularly sensitive for homes with flat monolithic roofs, often the weak acoustical link in the building envelope (i.e., building façade and roof). Also, closely packed residences may not allow for all rooms in a home to be measured, because it may not be possible to place the exterior loudspeaker in the required location for a given room.

Notes: Meas. = duraon of the text; ppl = people; Inst. = cost of the measuring equipment; RT = reverberaon me; RT60 = The me it takes for sound to decay 60 dB in a room. Large rooms with hard surfaces, such as concert halls, have reverberaon mes of around 2 seconds. Smaller rooms with sound absorbing surfaces have shorter reverberaon mes. 1) Correcons applied - Flyover: 2 A-weighted decibels (dBA), Exterior loudspeaker: 2 dBA, Interior loudspeaker: 5dBA. 2) Average NLR difference calculated by first averaging all of the NLR across all measurement methods (except interior loudspeaker and sound intensity), and then subtracng the NLR from one method (e.g., flyover) from the average NLR. Interior loudspeaker not used in average as this method does not follow naonal standards and the 5 dB ve“ed). correcon applied to the data is based on limited field measurements (i.e., not fully 3) Loudspeaker measurement accuracy would be improved if flush microphone posion is used instead of the 1 to 2 meter posion. 4) Costs based upon the best pracces outlined in this report, not current pracce for sound insulaon programs. Method Accuracy Uncertainty Logis cs Public Rela ons Repeatability Limita ons Meas: 5.3 hrs Instr: $260 Avg. Diff. = 0.4 dB Std. Dev. = 1.9 dB Analysis: 4.0 hrs Other: $23 Total: $1,473 Meas: 4.0 hrs x 2 ppl Instr: $65 Avg. Diff. = 1.4 dB Std. Dev. = 1.8 dB Analysis: 4.0 hrs Other: $18 Total: $1,600 Meas: 4.0 hrs x 2 ppl Instr: $65 Avg. Diff. = 0.5 dB Std. Dev. = 1.7 dB Analysis: 4.0 hrs Other: $618 Total: $2,200 Meas: 5.3 hrs Instr: $43 Avg. Diff. = 0.1 dB Std. Dev. = 2.9 dB Analysis: 4.0 hrs Other: $12 Total: $1,233 Survey: 5.3 hrs Instr: $0 Avg. Diff. = 0.7 dB Std. Dev. = 1.4 dB Analysis: 4.0 hrs Other: $12 Total: $1,190 Survey: 5.3 hrs Instr: $43 Avg. Diff. = 1.3 dB Std. Dev. = 2.1 dB Analysis: 6.0 hrs Other: $12 Total: $1,233 Meas: 4.0 hrs x 2 ppl Instr: $325 Analysis: 6.0 hrs Other: $18 Total: $2,110 Requires use of expensive instrument. Li“le effect. Disturbing to neighbors. Disturbing to neighbors. Truck may block traffic. Minor effect. Li“le effect. Minor effect. Likely. No standards exist. Flyover Exterior Ground Level Speaker Exterior Elevated Speaker Indoor Speaker IBANA Calculation Spreadsheet Calcula on (measured RT60) No standards or conformance tests. Conforms to Canadian standards. Conforms to known acouscal theory. Sound Intensity No. Yes. Yes. Yes. Yes. Straightforward. May be contaminated by high traffic noise levels. Straightforward. Requires on site survey of each room/building. Li“le effect. Yes.Straightforward. Straightforward. Requires vacant residence. May be contaminated by occupants or exterior noise (e.g., dog bark). Straightforward. Not feasible at some rooms due to lack of space/access to required exterior speaker locaon. Difficult with bucket truck. Not feasible at some rooms due to lack of space/access to required exterior speaker locaon. New method under development. Assumes built construction per computer database. Does not account for leaks or other building deficiencies. No. No. No. Assumes built construction per computer database. Does not account for leaks or other building deficiencies. Not ve“ed by acouscal consultant community; correcon factors required, but no clear guidance on what to use. No. Yes. Yes. Yes. Covered under FAA PGL 12 09 / Order 5100.38D? Requires substantial flight acvity. Themeasurement may not capture all aircra¡ types (e.g., package delivery aircra¡). Does not reach roof, leading to poor results for flat monolithic roofs. Access not always possible due to trees, buildings & wires. Cost/home Generally conforms to ASTM E966. Generally conforms to ASTM E966. Generally conforms to ASTM E966. Standardization Table 1-1. Matrix of acoustical testing methods.

Overview 9 The elevated loudspeaker method requires a bucket truck with hydraulic lift to be used. Closely packed residences may not afford sufficient room to maneuver the truck to elevate the speaker for measurement. Trees and utility lines often obstruct areas where the speaker should be elevated. Additionally, similar to the ground-level loudspeaker, it may not be possible to measure all rooms when residences are closely packed. The calculation method has few technical impediments, though currently it is often difficult to accurately determine the acoustical flanking (leaks) from a home survey. However, new meth- ods may be developed to minimize this shortcoming. Administrative issues are those where homeowner satisfaction may be affected by the mea- surement method. Most homeowners seem to intuitively trust the aircraft flyover method over other methods. Some skepticism has been expressed in the past over loudspeaker and computation NLR methods, however unfounded. It is important, in all cases when measuring the NLR improvement, to employ the same method for pre- and post-construction measure- ment. When measuring for qualification for the program under PGL/Order 5100.38D guide- lines, homeowners may be particularly sensitive about the measurement method because it may eliminate their eligibility for participation while a seemingly similar neighbor home may qualify. To the extent possible, it is advisable to use a single NLR measurement method throughout the neighborhood to minimize homeowner skepticism about the measurement process. Financial considerations are fairly straightforward by assessing the data in the Table 1-1 matrix. There is a natural desire to minimize measurement expense to allow for additional fund- ing for the actual noise insulation work. However, with the new PGL/Order 5100.38D guidelines, homeowners may be expected to challenge eligibility, perhaps by lawsuit, if they are eliminated from the program by pre-construction acoustical measurement. Therefore, in sensitive situa- tions it may be advisable to select the most accurate and reliable method from Table 1-3 despite an increased cost for measurement. Table 1-2. Decision matrix for acoustical testing method. Note: Shaded columns represent the suggested measurement methods. Measurement Issue Ai rcr a Fly ov er Ex te rio r G ro un d S pe ak er Ex te rio r E lev at ed Sp ea ke r Ind oo r S pe ak er IBA NA Ca lcu la on Sp re ad sh ee t C alc ula o n So un d I nt en sit y Method has been accepted for previous FAA testing X X X Testing may be repeated for verificaon X X X X Minimum disrupon to occupants X X Minimum disrupon to neighbors X X X X X Perceived as most credible by homeowners X Adequately measures poor roof ceiling assemblies X X X X X Runway use varies, limited flyover acvity X X X X X X Testing method supported by naonal standards or theory X X X X X Home must be vacant X Elevated interior noise levels (e.g., birds, dogs) X X X X X X X Home surrounded by trees or utility wiring X X X X X X Informaon on home construcon unavailable X X X X X Covered under FAA PGL/5100.38D X X X

10 Evaluating Methods for Determining Interior Noise Levels Used in Airport Sound Insulation Programs Based on the research team’s findings, the aircraft flyover and exterior loudspeaker meth- ods provide the best results. Sound intensity and indoor speaker methods show promise for future measurements, but additional research and standardization of the measurements is necessary. Acoustical calculations generally provide accurate results; however, it is possible to miss flanking paths (sound leaks) during the field survey that would result in overstatement of the NLR. 1.5 Measurement Uncertainty—Present and Future As part of data analysis, the research team used national and international standards for acous- tical measurement to correlate and correct measurement results obtained. While the research team was able to measure and analyze the uncertainties associated with the measurements, there are other known factors to influence measurement results. This proved most important for external loudspeaker and microphone position for the flyover and speaker measurements. Table 1-3 shows the measurement uncertainties for current measurement practices and best practices outlined in Section 1.6. The aircraft flyover, exterior speaker, and sound intensity methods are assessed. The cumulative margin of error is given in the second column adjacent the measure- ment method; this is the convolution of the individual uncertainties for each measurement method and technology. Appendix D provides detailed information on how the measurement uncertainty was calculated. The above margins of error are for the absolute measurement conditions and not for the relative measurements. Relative measurement uncertainty will be less because some of the uncertainty factors such as instrument error would be nearly the same for the pre- and post- construction NLR measurements. Method Field Meas. Margin of Error Calculated Total Margin of Error Outdoor Measurement Factors Interior Measurement Factors Meteor ology Ground Dip Mass air mass resonanceLocaon Ambient Instrument Locaon Ambient Instrument Exisng Pracce Aircra flyover ± 1.9 ± 1.9 1.2 0.5 0.4 0.4 0.5 0.4 1.0 0.5 Speaker outside ± 1.8 ± 1.9 1.3 0.3 0.4 0.4 0.3 0.4 0.5 0.3 1.0 Best Pracce Aircra flyover ± 1.4 0.2 0.5 0.4 0.2 0.5 0.4 1.0 Speaker outside ± 1.1 0.2 0.3 0.4 0.2 0.5 0.4 0.5 0.2 0.5 Intensity ± 0.9 0.4 0.3 0.4 0.4 0.3 0.4 Notes: 1. Assume no significant grazing incidence (when the angle formed between the façade surface and noise source approaches zero). Accurate measurements are not possible with significant grazing incidence. 2. Flyover method: Assumes only aircra with a 10 dB or higher signal to noise ra…o used. 3. Loudspeaker: Assumes only data with a 10 dB or higher signal to noise ra…o used. 4. Loudspeaker Best Prac…ce: Assumes four loudspeaker posi…ons, two surface mounted microphones (exterior) per wall/roof, and interior spa…al average/manual scan. Table 1-3. Calculated measurement uncertainty.

Overview 11 1.6 Acoustical Testing Best Practices Careful measurement protocol will minimize measurement uncertainties, particularly for the relative measurements. All measurement conditions should be carefully documented with field notes and photographs, with particular attention given to measurement locations. Ambient noise levels and sources, aircraft operations, meteorological conditions, and measurement team should be noted. This will be particularly true for the relative post-construction measurements, where accurately replicating the original measurement conditions will minimize uncertainty. Table 1-4 summarizes the best practices for each measurement method. 1.6.1 Best Practices for Aircraft Flyover Measurements 1. Measurements should be conducted in vacant homes, as occupant noise contamination readily occurs. 2. Consultants should review the general operations of each airport to ensure that the aircraft spectrum being used (based on the airport’s fleet mix) is from the INM/AEDT study qualify- ing the sound insulation program. Special selection of fleet mix to be used may be required in special cases such as military operations occurring at night. 3. Outdoor microphones should be set in the free field or flush mounted to the ground or build- ing façade. Near field measurement, 1 to 2 m from the façade, is not recommended. 4. Measurements should be made in one-third octave bands from 50 Hz through 5 kHz or octave bands from 63 Hz through 4 kHz; the A-weighted value (see Section 3.2.1.3: Frequency Weight- ing) should be computed from these frequency ranges, rather than using the A-weighted value calculated by the sound level meter. 5. Measurement sample time should not be faster than every 0.5 sec (500 ms). See Section 4.1.1. 6. In general, raw noise reduction is higher with the flyover measurement method than the loudspeaker measurement method; a correction of 2 to 4 dB is recommended to compensate for ground reflection and/or reflected noise off the façade under test. 7. The preferred statistical analysis (1) computes the mean NLR values for all events, (2) orders all NLR values from highest to lowest standard deviation, and (3) sequentially deletes the NLR event with the highest standard deviation computing a new mean, standard deviation, and desired confidence interval. This process, deleting the top value with the highest standard deviation, is repeated until the desired mean, standard deviation, and confidence interval are achieved. The procedure and example are found in Section 4.1.2. 8. A single properly placed microphone in interior rooms is adequate for most NLR measurements. 1.6.2 Best Practices for Ground-Level Exterior Loudspeaker 1. The loudspeaker should be located approximately 6 to 12 m (20 to 40 feet) away from the façade for typical homes; adequate sound levels (e.g., 90 dB minimum) should be generated at the façade to overcome background noise. For rooms with multiple façades (e.g., corner rooms), the loudspeaker should be positioned to generate diffuse sound levels. Noise levels along the façades should not vary by more than 3 dB. 2. Measurements should be made in one-third octave bands from 50 Hz through 5 kHz or octave bands from 63 Hz through 4 kHz; the A-weighted value should be computed, rather than from direct A-weighted measurement. 3. For the exterior (source measurement), the roof should be measured if the noise level at the roof is within 10 dB of the noise level of the wall. 4. For the exterior measurement position, four loudspeaker positions should be used (e.g., 30°, 45°, 60°, 75°). The results should then be averaged using the weighting outlined in ASTM (American Standard for Testing and Materials) E966 (ASTM 2010).

TestMethod Source Locaon Source Microphone Source Correcon ReceiverMicrophone Receiver Correcon Locaon (Reference) Location (Reference) Flyover Airborne (aircra) Free field above ground Interior away fromwalls, 0 dB measuring diffuse field 10m to bldg/1.5m elev 2m off facade 2 dB 0 dB Exterior Ground- (far field) (spatial average) (ASTME966) Level Speaker 10m to bldg / 1.5m elev flush to facade recommend 5 dB 0 dB (far field) (2 locs per wall/roof) (ASTME966) 10m to bldg / above roof 2m off facade 2 dB 0 dB Exterior Elevated (spaŒal average) (ASTME966) Speaker 10m to bldg / above roof flush to facade recommend 5 dB 0 dB (2 locs per wall/roof) (ASTME966) Exterior flush mounted ? research needed Indoor Speaker Room corner, producing Moving microphone, diffuse sound field measuring diffuse 2m off facade ? research needed field (near field) Exterior flush mounted ? research needed Sound Intensity Room corner, producing Moving microphone 0 dB diffuse sound field measuring diffuse 2m off facade ? research needed field (near field) 2 to 4 dB, due to ground reflecŒon and reflecŒon from building facade 5 dB, due to reverberant build up; research needed Interior away fromwalls, spatial average Interior away fromwalls, spatial average Interior away fromwalls, spatial average Interior away fromwalls, spatial average Table 1-4. Best practices summary table.

Overview 13 5. Exterior microphones should be flush mounted where possible, rather than 1 to 2 m (3 to 6 feet) off the façade. For the flush mount, at least two microphone positions per façade and/ or roof should be used (e.g., a corner room without a roof measurement would yield four positions). 6. Measurements should be halted during aircraft flyovers. This requires two technicians (one outdoor and one indoor) and a visual or non-auditory alert system so the interior measurement can be halted during a flyover. 7. Other practices outlined in ASTM E966 should be followed, such as subtraction of back- ground noise, spatial averaging (manual scanning) in the room, etc. 1.6.3 Best Practices for Elevated Exterior Loudspeaker 1. The loudspeaker should be located approximately 6 to 12 m (20 to 40 feet) away from the façade for typical homes; the loudspeaker should be elevated above the roof plane. Adequate sound levels (e.g., 90 dB minimum) should be generated at the façade to overcome back- ground noise. For rooms with multiple façades (e.g., corner rooms), the loudspeaker should be positioned to generate diffuse sound levels. Noise levels along the façades should not vary by more than 3 dB. 2. Measurements should be made in one-third octave bands from 50 Hz through 5 kHz or octave bands from 63 Hz through 4 kHz; the A-weighted value should be computed, rather than direct A-weighted measurement. 3. For the exterior (source measurement), the roof should be measured. 4. For the exterior measurement position, four loudspeaker positions should be used (e.g., 30°, 45°, 60°, 75°); the four angles can be achieved in the horizontal and/or vertical plane. The results should then be averaged using the weighting outlined in ASTM E966. 5. Exterior microphones should be flush mounted where possible, rather than 1 m to 2 m (3.3 ft. to 6.6 ft.) off the façade. For the flush mount, at least two microphone positions per façade and/or roof should be used (e.g., a corner room with roof would yield six positions). 6. Measurements should be halted during aircraft flyovers. This requires two technicians (one outdoor and one indoor) and a visual or non-auditory alert system so the interior measure- ment can be halted during a flyover. 7. Other practices outlined in ASTM E966 should be followed, such as subtraction of back- ground noise, spatial averaging (manual scanning) in the room, etc. 1.6.4 Best Practices for Interior Loudspeaker Since there is no national/international standard for the interior loudspeaker noise reduction measurement, the research team has not provided best practices. Additional research is neces- sary to standardize this measurement and determine which correction factors are required for the data to be comparable to the exterior loudspeaker and flyover measurements. 1.6.5 Best Practices for Acoustical Calculations 1. Compute the composite transmission loss (CTL) for all façades receiving flyover noise using dimensions from field drawings and reliable TL data for the building elements. 2. It is not necessary to measure reverberation time in typical rooms; rather, the research team proposes utilizing typical, conservative reverberation times to adjust the calculated noise reduction. 3. A laser glass gauge or similar should be used during the field survey to determine the exact glazing configuration of the windows. Close review of door gasketing and other fenestration elements is warranted to estimate the “leakiness” of components.

14 Evaluating Methods for Determining Interior Noise Levels Used in Airport Sound Insulation Programs 4. It is not generally necessary to consider flanking transmission from air infiltration, because CTL need only be computed in the frequency range 50 Hz through 5 kHz where flanking effects are minimal. 5. Acoustical calculations should be calibrated/back-checked via acoustical measurements. For example, if calculations are performed on 100 homes, then 10 homes should be acoustically tested to verify the calculation model. 1.6.6 Best Practices for Air Infiltration There was no correlation observed between the air infiltration results from blower door test- ing and measured noise reduction. Thus, the research team does not recommend utilizing air infiltration to predict noise reduction and has not proposed the procedure in best practices. 1.6.7 Best Practices for Acoustic Intensity Since there is no national/international standard for sound intensity measurements of the type required, the research team has not provided best practices in this area. Additional research is necessary to standardize this measurement and determine which correction factors are required for the data to be comparable to the exterior loudspeaker and flyover measurements. Intensity is included here because it has the potential for becoming “the” best practice. In addi- tion to its low measurement uncertainty and immunity from factors that affect other methods, it is the only method that can be used equally well at any airport in the world.

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TRB's Airport Cooperative Research Program (ACRP) Report 152: Evaluating Methods for Determining Interior Noise Levels Used in Airport Sound Insulation Programs provides guidance for selecting and implementing methods for measuring noise level reduction in dwellings associated with airport noise insulation programs. The report complements the results of ACRP Report 89: Guidelines for Airport Sound Insulation Programs.

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