Fundamentals of Acoustics and Noise

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University of New South Wales *

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9325

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Mechanical Engineering

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Oct 30, 2023

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Fundamentals of Acoustics and Noise MECH9325 Term 2, 2023 LAB 1 (Date of Submission: 27/06/2023) 1

Table of Contents Task 1 ......................................................................................................................................... 1 Task 2 ......................................................................................................................................... 2 Task 3 ......................................................................................................................................... 5 References .................................................................................................................................. 6 Table of Figures Figure 1: Time history of the sound pressure level of the Pacific Highway recording, measured over a 3-minute period ............................................................................................... 1 Figure 2: Time history of the sound pressure level of the anchor drilling site, measured over a 60 second period ........................................................................................................................ 2 Figure 3: Time history of the sound pressure level of the hydraulic rock breaker, measured over a 60 second period .............................................................................................................. 3 Figure 4: Time history of the sound pressure level of the excavator, measured over a 60 second period ............................................................................................................................. 3 Figure 5: Time history of the sound pressure level of the garbage trucks unloading, measured over a 60 second period .............................................................................................................. 4 Table of Figures Equation 1: Equation used to find the equivalent A-weighted SPL over total time T ............... 2 i

Task 1 0.28 6.22 12.17 18.11 24.06 30 35.9 4 41.8 9 47.8 3 53.7 8 59.7 2 65.6 7 71.6 1 77.5 5 83.5 89.44 95.39 101.33 107.28 113.22 119.17 125.11 131.05 137 142.94 148.89 154.83 160.78 166.72 172.66 178.61 0 10 20 30 40 50 60 70 80 90 Time History of Sound Pressure Level for the Pacific Highway Recording OverallLevel LAEQ LA10 LA90 Time (seconds) Sound Pressure Level (dB(A)) Figure 1: Time history of the sound pressure level of the Pacific Highway recording, measured over a 3-minute period. Using the iNVH application and the Pacific Highway recording, a time history of the sound pressure level (dB(A)) of the recording was produced over a sampling period of 3 minutes. Using an Excel spreadsheet, the values of L Aeq , L A10 , and L A90 were derived. For L Aeq , the time interval between each measurement taken was calculated and substituted into Equation 1 alongside its respective instantaneous sound pressure level to find the L Aeq of the entire sample, which was found to be 69.29 dB(A). The values of L A10 and L A90 were calculated using the Excel functions PERCENTILE (array, 0.9) and PERCENTILE (array, 0.1), and were found to be 74.39 dB(A) and 54.12 dB(A) correspondingly. This data can be seen on Figure 1. L Aeq refers to the equivalent A-weighted sound pressure level over the entire period, as such, all sound affects the value of L Aeq as it seeks to describe what is the average noise level over a period [CITATION Dep16 \l 3081 ]. L A10 refers to instances where the sound pressure level measured was equal to or exceeded for 10% of the measurement period [CITATION Dep16 \l 3081 ]. This refers to instances of louder noise, such as the appearance of a heavy vehicle, a small vehicle close to the audio capturing device, or of an abundance of traffic passing by. Likewise, L A90 represents periods where the sound pressure level was equal to or exceeded for 90% of the time. Hence, L A90 describes the ambient noise and therefore, details the sound pressure level of the background noise of the recording, including things like the beeping of the pedestrian crossing signal, wind, etc. ii

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Equation 1: Equation used to find the equivalent A-weighted SPL over total time T Task 2 0.09 2.14 4.18 6.22 8.27 10.31 12.35 14.4 16.4 4 18.4 8 20.5 3 22.57 24.61 26.66 28.7 30.7 4 32.7 9 34.8 3 36.8 7 38.92 40.96 43 45.05 47.0 9 49.1 3 51.1 8 53.2 2 55.26 57.31 59.3 5 0 10 20 30 40 50 60 70 80 Time History of Sound Pressure Level of the Anchor Drilling Site OverallLevel LA90 LAMIN LAMAX LAEQ Time (seconds) Sound Pressure Level (dB(A)) Figure 2: Time history of the sound pressure level of the anchor drilling site, measured over a 60 second period. iii

0.09 1.95 3.81 5.67 7.52 9.38 11.2 4 13.1 14.95 16.8 1 18.67 20.5 3 22.38 24.24 26.1 27.96 29.81 31.6 7 33.5 3 35.39 37.2 4 39.1 40.9 6 42.82 44.68 46.5 3 48.3 9 50.25 52.1 1 53.96 55.82 57.6 8 59.54 0 10 20 30 40 50 60 70 80 90 Time History of Sound Pressure Level of Garbage Trucks Unloading OverallLevel LA10 LA90 LAMAX LAEQ Figure 5: Time history of the sound pressure level of the garbage trucks unloading, measured over a 60 second period. Steady noise, impulsive noise, and intermittent noise are three categories of noise often used to describe the noise present on a construction site or where heavy machinery is being operated. Steady noise refers to situations wherein there is a constant noise that only fluctuates in a 3 dB(A) range, intermittent refers to noise that fluctuates greater than 5 dB(A), whereas impulsive refers to short, sudden ‘impulses’ of sound pressure level that last less than a second and are much louder than the background noise [ CITATION Dep20 \l 3081 ]. For the recording of the anchor drilling site, its sound type can be described as an impulsive sound due to the sudden manoeuvring of heavy machinery, air release, and metal falling on metal which is laid against a quieter background noise consisting of the running of different generators, pumps, boring, and idling machinery. This can be seen in Figure 2, where the sound pressure level often fluctuates greater than 5 dB(A) for less than a second. For the recording of the hydraulic rock breaker, the sound type can be characterised as an intermittent noise due to the repetitive hammering, which also results in a fluctuation of more than 5 dB(A) over the measured time. This is reflected in Figure 3, which clearly illustrates the fluctuations in sound as a result. Similarly, the recording of the excavator can also be classified as an intermittent sound. From Figure 4, although most of the graph describes a steady noise when the excavator is being used to dig, when the excavator is being v

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manoeuvred an intermittent sound can be heard due to the beeping that it emits when reversing. Finally, the recording of the garbage trucks unloading can be categorised as a steady noise, as there is no noise fluctuation present in the recording that is above 3 dB(A). For the series of recordings, the noise descriptors that were chosen were comprised of L AMIN, L AMAX , L Aeq and L A90 . L AMIN and L AMAX refers to the minimum and maximum sound pressure level values that are collated over the length of a recording. The purpose of these noise descriptors is to describe the impact of any potential intermittent or impulsive noise on listeners. L Aeq refers to the average sound pressure level of an environment over time. This is a key descriptor as it incorporates all sound types and produces a mean sound pressure level which a person experiences to ensure that an individual is operating at a safe level of noise exposure. In addition, the L Aeq descriptor is used in Australia under the Australian standard AS1269.1-1998. L A90 alludes to the sound pressure level that is present for 90% of the measured period, this descriptor usually indicates the steady ambient sound pressure level. This descriptor can be used to certify that the background noise does not exceed a dangerous level throughout the length of the recording. Task 3 The recordings of the anchor drilling site, hydraulic rock breaker, excavator and of the garbage trucks unloading had an L Aeq of 61.28 dB(A), 62.79 dB(A), 60.69 dB(A), and 68.65 dB(A) respectively. When using L Aeq as a descriptor for different types of anthropogenic environmental noise, it considers all types of noise – steady, intermittent, and impulsive noise – and dispenses an average sound pressure level for the period measured. When there are short term sound events, such as those with an impulsive sound type, it can skew the L Aeq value and result in an inaccurate average sound pressure level. As a result, it is unsuitable for cases where the sound source of interest emits a constant noise and where the ambient noise has a degree of fluctuation [ CITATION NSW23 \l 3081 ]. vi

References [1]Department of Transport and Main Roads, Queensland Government, “Transport Noise Management Code of Practice: Volume 2 – Construction Noise and Vibration,” 29 July 2016. [Online]. Available: https://environment.des.qld.gov.au/__data/assets/pdf_file/0027/88560/eis-tm-noise- measurement-manual.pdf. [Accessed 24 June 2023]. [2]Department of Transport and Main Roads, Queensland Government, “Noise Measurement Manual,” 10 March 2020. [Online]. Available: https://environment.des.qld.gov.au/__data/assets/pdf_file/0026/88703/pr-cp-noise- and-vibration.pdf. [Accessed 24 June 2023]. [3]NSW Environment Protection Authority, “Noise Guide for Local Government Part 2 Noise assessment,” January 2023. [Online]. Available: https://www.epa.nsw.gov.au/~/media/EPA/Corporate %20Site/resources/noise/130127NGLGPart2.ashx. [Accessed 26 June 2023]. vii