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From page 52... ... 52 This chapter provides guidance for meeting FAA acoustical requirements for SIPs, an overview of the acoustical engineer's role on the SIP team, and a general background to the acoustical concepts, metrics, and nomenclature used for airport noise, which is important to understanding how noise is perceived, measured, and depicted. Noise is defined as unwanted sound and is therefore a relative term that depends on the disposition of the individual listener as well as the sound source. Read the entire page →
From page 53... ... Acoustical Engineering 53 Three aspects of noise are important in determining subjective response: 1. Level (i.e., magnitude or loudness) Read the entire page →
From page 54... ... 54 Guidelines for Airport Sound Insulation Programs A doubling of sound energy (for instance, from two identical automobiles passing simultaneously) creates a 3-dB increase; the resultant sound level is the sound level from a single passing automobile plus 3 dB. Read the entire page →
From page 55... ... Acoustical Engineering 55 4.1.4 Noise Exposure Noise exposure refers to a measure of noise over a period of time, whereas noise level is a value at an instant in time. Although a single sound level may adequately describe the noise at any instant in time, airport and other community noise levels vary continuously. Read the entire page →
From page 56... ... 56 Guidelines for Airport Sound Insulation Programs may be more reliably repeated and because the duration of the transient event is incorporated into the measure (thereby better relating to subjective response) Read the entire page →
From page 57... ... Acoustical Engineering 57 evening (i.e., 7:00 p.m. Read the entire page →
From page 58... ... 58 Guidelines for Airport Sound Insulation Programs 3. An increase or decrease in level of at least 5 dB is required before any noticeable change in response would be expected. Read the entire page →
From page 59... ... Acoustical Engineering 59 However, each room receives a slightly different NLR improvement, but each room receives a similar interior noise environment after retrofit. In the third approach, the exterior envelope of the whole building is reviewed for consistency of construction and building elements, and then individual rooms are verified for specific performance issues. Read the entire page →
From page 60... ... 60 Guidelines for Airport Sound Insulation Programs Designing for a 5-dB NLR improvement in a room requires the application of technical calculations containing information on the room area, the amount of wall openings, and the projected performance of the new treatments. Some examples of these calculations can be found in the 2005 version of the SIP guidelines.13 Rooms with varying amounts of wall openings will necessarily achieve different NLR improvements from a standardized program approach to window and door replacement. Read the entire page →
From page 61... ... Acoustical Engineering 61 does not address factoring in a margin of error. There may be homeowners who will be deemed ineligible by testing that has not accounted for a margin of error. Read the entire page →
From page 62... ... 62 Guidelines for Airport Sound Insulation Programs Users of these updated guidelines are advised that further clarification from the FAA may occur. In response to these issues, a testing strategy is being formulated that uses a combination of typology sample testing with computer modeling. Read the entire page →
From page 63... ... Acoustical Engineering 63 The most fundamental principle of sound TL is the mass law, which gives the TL at each frequency as a function of surface weight. According to the mass law, TL increases linearly with an octave or one-third octave band. Read the entire page →
From page 64... ... 64 Guidelines for Airport Sound Insulation Programs The sound TL properties of building elements are tested and reported according to national standards in one-third octave bands, classified as an STC rating.21 Each building element, such as a particular window, may be expected to have a unique TL signature represented by 16 TL values from 125 Hz to 4000 Hz. As mentioned in the previous section discussing mass law, the nature of sound attenuation through structures is such that all TL tests have generally up-sloping properties from low frequency to high frequency, indicating generally increasing noise reduction in higher frequencies. Read the entire page →
From page 65... ... Acoustical Engineering 65 Another TL standard was adopted by ASTM, the outdoor–indoor transmission class (OITC) .22 The OITC method is simpler and more easily understood than STC. Read the entire page →
From page 66... ... 66 Guidelines for Airport Sound Insulation Programs • Addition of attic insulation. Often fiberglass insulation is added by blowing in, although roll out insulation works equally well. Read the entire page →
From page 67... ... Acoustical Engineering 67 Other metrics for noise-related impacts such as speech interference and sleep interference may be useful to help evaluate specific use areas such as hospitals, schools, and places of worship. While the interior DNL ≤ 45 dB and ∆NLR ≥ 5 dB metrics are the measurement standards for SIP performance, the use of other metrics is only allowed by the FAA with specific approval in concert with the regional ADO. Read the entire page →
From page 68... ... 68 Guidelines for Airport Sound Insulation Programs 4.6 Acoustical Testing The program objectives are to meet the interior DNL ≤ 45 dB and ∆NLR ≥ 5 dB on the basis of the design year NEM (which, per PGL 05-04, must be currently valid) Read the entire page →
From page 69... ... Acoustical Engineering 69 using this laboratory-based method, even though an interior room approximates one room with a diffuse sound field. The sound field outside the structure constitutes both a free field, not influenced by local sound reflection, and a far field, not close to or influenced by the noise source size. Read the entire page →
From page 70... ... 70 Guidelines for Airport Sound Insulation Programs • A single stationary microphone in a room does not give a good measure of the diffuse sound field. Laboratory tests use large rooms of special dimensions, often with moving microphones or vanes, and nonparallel walls to minimize standing wave effects. Read the entire page →
From page 71... ... Acoustical Engineering 71 ties of the receiving room. Therefore, if there is a considerable change in room furnishing between the pre- and post-retrofit testing, a significant change in room absorption will affect the measured NLR. Read the entire page →
From page 72... ... 72 Guidelines for Airport Sound Insulation Programs test method or which provides the most accurate and reliable results. However, most consultants appear to agree on the following limitations and benefits of the two common methods: • It is advantageous to have flyovers for the sound source since they provide the most realistic acoustical environment for testing. Read the entire page →
From page 73... ... Acoustical Engineering 73 MEASURED DNL VALUES TRUE MEASUREMENT ERROR DNLin -3 -2 -1 0 +1 +2 +3 42 39 40 41 42 43 44 45 43 40 41 42 43 44 45 46 44 41 42 43 44 45 46 47 45 42 43 44 45 46 47 48 46 43 44 45 46 47 48 49 47 44 45 46 47 48 49 50 48 45 46 47 48 49 50 51 Correctly eligible -- True positive (lower right) Incorrectly eligible -- False positive (upper right) Read the entire page →

From page 52...

... 52 This chapter provides guidance for meeting FAA acoustical requirements for SIPs, an overview of the acoustical engineer's role on the SIP team, and a general background to the acoustical concepts, metrics, and nomenclature used for airport noise, which is important to understanding how noise is perceived, measured, and depicted. Noise is defined as unwanted sound and is therefore a relative term that depends on the disposition of the individual listener as well as the sound source.