代写MECH9325、代做Java/Python程序语言

日期：2024-06-26 10:01

UNSW Sydney

School of Mechanical and Manufacturing Engineering

MECH9325 Fundamentals of Acoustics and Noise

Laboratory 1 – Descriptors for time varying noise levels

Due date: Tuesday 25 June 5pm (Moodle online submission)

1. 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.

2. Tasks

Task 1

Create an x-y plot showing (i) the instantaneous sound pressure level in dB(A), (ii) LAeq, (iii) LA10 and (iv)

LA90 from the traffic noise recording over a sampling period of 3 minutes. See Figure 1 for an example.

Examine the quantitative data and provide a brief description (no more than 300 words) describing the

types of sounds that have influenced LAeq, LA10 and LA90.

Figure 1 Time history of a sound pressure level

To complete Task 1, you will need to follow the steps below:

1) Download the “Decibel X” free sound level meter app on your smartphone. This is available on both

iOS and Android.

Figure 2 Decibel X sound level meter app

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 below, 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

below, you should see the Sound level meter screen in Figure 4(a).

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 3 minutes. 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.

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, 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 interval time in a second column.

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.

(a) Sound level meter screen

(b) Data screen

Figure 4 Decibel X sound level meter app

Figure 5 Excel data important screen

Task 2

Refer to each of the recordings in the YouTube links below. Measure noise over a sampling period of

1 minute for each recording. Select appropriately from the following descriptors LA1,1min, LA10,1min,

LA90,1min, LAeq,1min, LAmax and LAmin to evaluate the different sound recordings. Create an x-y plot showing

the relevant noise descriptors for each recording across a 1-minute sampling period. See the Appendix for

Excel commands to calculate different noise descriptors. In your discussion, differentiate between steady

noise, impulsive noise and intermittent noise. This task should include the time history of each recording

and computed noise descriptors.

Anchor drilling site - https://www.youtube.com/watch?v=Av_6CCRF7Qc

Hydraulic rock breaker - https://www.youtube.com/watch?v=2xXEk0TtOiE

Scrapyard - https://www.youtube.com/watch?v=08vuXspuhWg

Concrete recycling - https://www.youtube.com/watch?v=RxZyvNwoP-k

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.

3. 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://environment.des.qld.gov.au/__data/assets/pdf_file/0026/88703/pr-cp-noise-and-vibration.pdf

Hint: search for intermittent within this document for useful information, for example, see pages 11

and 12.

Noise Guide for Local Government (old version)

Although this document has been superseded, it is still useful guide on how to measure

environmental noise, see section 2.3.

Noise Guide for Local Government (current version)

This document provides guidance on how to measure environmental noise, see section 6.6.

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)