School of Mechanical and Manufacturing Engineering
MECH9325 Fundamentals of Acoustics and Noise
Laboratory 1 – Descriptors for time varying noise levels
Due date: Monday 17 March 5pm (Turnitin submission)
Introduction
The aim of this virtual lab is to examine the suitability of different sound level parameters for different noise events. This will be achieved by calculating the variability in LAeq and LN for several types of sounds corresponding to traffic noise and other anthropogenic sounds.
Tasks
Task 1
Create an x-y plot from the traffic noise recording over a period of 30 seconds showing (i) the instantaneous sound pressure level in dB(A), (ii) LAeq, (iii) LA10, (iv) LA90 . See Figure 1 for an example (note that Figure 1 shows a traffic noise recording over a period of 180 seconds).
Within your 30 second recording, examine the quantitative data and provide a brief summary (no more than 300 words) identifying the various sounds and how they have influenced LAeq, LA10 and LA90.
Figure 1 Time history of a sound pressure level
To complete Task 1, you will need to conduct the following steps:
1) Download the “Decibel X” free sound level meter app on your smartphone (see Figure 2). This is available on both iOS and Android.
2) Setup the app by following the guided setup. Select your language and enable microphone use. Ensure that you do not sign up for the paid Pro version.
If you arrive at the screen as shown in Figure 3, click in the top right corner to exit from this screen (there is a hidden cross). Do not click Try It Free as you may be asked to enter payment details. Once you exit from the Pro version sign-up screen shown in Figure 3, you should see the Sound level meter screen in Figure 4(a).
Figure 2 Decibel X sound level meter app
Figure 3 Pro version sign-up screen
3) Experiment with the ‘play’, ‘pause’, ‘download ’ and ‘reset ’ buttons in Meter (see Figure 4(a)). Also note the Data menu (see Figure 4(b)).
4) Place your smartphone in a fixed and secured position so you can be hands free.
5) Play the traffic noise audio file on a device other than your phone (see Lab 1 channel in Teams).
6) Click on the ‘play’ button (see Figure 4) to start recording for a sampling period of 30 seconds. We recommend you perform. this in a noise-controlled environment (for example, a room with all windows and doors closed).
7) Observe the temporal variation in SPL, across the frequency spectrum.
8) Click the ‘pause’ button to stop the recording.
9) Click the ‘download’ button to save your recording.
(a) Sound level meter screen
(b) Data screen
Figure 4 Decibel X sound level meter and data screens
10) Navigate to the ‘data’ menu. Locate your recording and click on it. In the top right corner, click the ‘share’ icon, select “.CSV”, and choose an appropriate way to export your data to your computer (we recommend exporting via email or OneDrive, so you can access the file on your computer).
11) On your computer, download and save your file. You may need to extract a .zip folder containing your data. Your data will be stored in a .txt file format.
12) Open a blank excel sheet that you would like to import the data into. In Excel, navigate to the “Data” ribbon and select “From Text/CSV” . Then, in the Windows Explorer window, navigate to and select your downloaded .txt audio data.
13) In the pop-up window as shown in Figure 5, ensure that the settings are selected as shown (Western European; Comma; etc). Then, click “Load” . You should have an Excel file with your measured A- weighted sound pressure levels in a column, and the time stamp in a second column. Note that the sampling period is 0.2 s.
14) Calculate LAeq, LA10 and LA90 and produce a similar x-y plot as shown in Figure 1. LAeq can be calculated from the A-weighted instantaneous sound pressure level for each time interval Ti of 0.2 seconds and the total time T of your sampling period (see Unit 2 lecture notes, Eq. 2.16). See the Appendix for Excel commands to calculate different noise descriptors.
Figure 5 Excel data import screen
Task 2
Refer to each of the links below, which take you to the start ofa noise event for different YouTube videos. For each video measure noise from the start of the noise event over a period of 30 seconds. For each recording, create and present an x-y plot showing the instantaneous sound pressure level in dB(A). Discuss if the noises should be classified as steady noise, impulsive noise and/or intermittent noise. Refer to the supplementary material to aid your discussion. The following descriptors may be required in your analysis: LA1, LA10, LA90, LAeq, LAmax and LAmin. Refer to the Appendix for Excel commands to calculate different noise descriptors. Include the relevant descriptor(s) on the x-y plot for each recording.
Anchor drilling site -https://youtu.be/Av_6CCRF7Qc?t=345
Hydraulic rock breaker -https://youtu.be/2xXEk0TtOiE?t=1
Pile driving -https://youtu.be/a7l5fhbQu5I?t=165
Garbage truck unloading -https://youtu.be/_y1ipVNXHTk?t=28
Task 3
Referring to the observations made during Tasks 1 and 2, discuss the limitations of LAeq when describing different types of anthropogenic environmental noise.
Submission
Submit your responses to Tasks 1 to 3 in a pdf file to the Lab 1 submission link in Moodle. The main body of your report (excluding the cover page and any appendices) should not exceed 5 pages.
Supplementary Material
• AS 1055:2018 Acoustics – Description and measurement of environmental noise
This document includes information on different noise descriptors, different types of sound, information to be recorded for general sound level surveys, for example, see sections 3, 6.5, 7 and Appendix E. (pdf is uploaded in Teams)
• Transport Noise Management Code of Practice: Volume 2 – Construction Noise and Vibration
https://www.tmr.qld.gov.au/business-industry/Technical-standards-publications/Transport-noise- management-code-of-practice.aspx
SeeLink to the 2023 Code hosted at the Department of Environment and Science
Hint: search for intermittent within this document for useful information, for example, see pages 12 and 13.
• Noise Guide for Local Government (current version)
Noise guide for local government | EPA
This document provides guidance on how to measure environmental noise, see section 6.6.
• Noise Guide for Local Government (old version)
Noise Guide for Local Government
Although this document has been superseded, it is still useful guide on how to measure environmental noise, see section 2.3 on page 59 of the document.
• FHWA Highway Traffic Noise Prediction Model
This document provides a wealth of information on traffic noise prediction and relationship between LA10 and LAeq for traffic noise, for example, see page 54.
(pdf is uploaded in Teams).
Appendix
In Excel, the PERCENTILE.INC(array, k) function calculates the kth percentile for a set of data, inclusive of the start and end values, where k is 0 to 1. The 80th percentile (k=0.8) provides the value for which 80% of the data points are smaller and 20% are greater. That is, k=0.8 corresponds to LA20 .
LA1 = PERCENTILE.INC(array, 0.99)
LA10 = PERCENTILE.INC(array, 0.9)
LA90 = PERCENTILE.INC(array, 0.1)
LAmin = MIN(array)
LAmax = MAX(array)