What Is the Optimal Position for an Acoustic Barrier to Reduce Road Noise?

[laheer]

Hi, I am new to this forum and I'm not sure if I have selected the correct area to post this question. If you think I should move it then let me know! As you can see, I have worked out part of the question but I am stuck when it comes to doing the second half. Any help would be appreciated! Thanks.

Homework Statement

Assume that your property is situated adjacent to a major road and the occupants are complaining about excessive noise levels. The noise source on the road is 45m away from the rear façade of your property. Measurements made at a distance of 4m from the noise source give an SPL of 85dB.

An acoustic barrier is to be erected between the road and your house. The barrier cannot be situated closer than 4m to either the road or the house and cannot be more than 2.5m high.

Calculate the SPL at the rear façade of your property before the barrier is erected.

Determine the best position for the acoustic barrier and calculate the SPL at the rear façade of you’re property when the barrier is in position.

Homework Equations

SPL = a + (b x NR)
or
L2 = L1 - 20. Log r2/r1

The Attempt at a Solution

L2 = 85 - 20. Log 45/4

L2 = 63.98

 

[jbsteele]

dBThis is the SPL at the rear façade of the property before the barrier is erected. For the best position of the acoustic barrier, the distance between it and the road should be the same as the distance between it and the house (4m). This will ensure that the sound level is reduced equally on both sides of the barrier. L3 = 63.98 - 20. Log 8/4 L3 = 57.98 dBThis is the SPL at the rear façade of the property when the barrier is in position.

 

[nlightner]

dB



Hello and welcome to the forum! I can assist you with your question about sound pressure level. It seems like you have already made some progress in your calculations, so I will provide additional information to help you complete the second half of the question.

Sound pressure level (SPL) is a measure of the sound pressure at a particular location, relative to a reference pressure level. In this case, the reference pressure level is 20 micropascals (µPa). SPL is commonly measured in decibels (dB), which is a logarithmic unit that represents the ratio of two sound pressures.

To calculate the SPL at the rear façade of your property before the barrier is erected, you can use the equation SPL = L1 - 20*log(r1/r0), where L1 is the SPL at a distance of 4m from the noise source (85dB in this case), r1 is the distance from the noise source to the measurement location (45m in this case), and r0 is the reference distance (1m in this case). Plugging in these values, we get:

SPL = 85 - 20*log(45/1) = 85 - 20*1.6532 = 53.05 dB

This means that without any barrier, the sound pressure level at the rear façade of your property would be 53.05 dB.

To determine the best position for the acoustic barrier, we need to consider the concept of sound diffraction. Sound waves can bend around obstacles, which means that the barrier does not need to be directly between the road and your house to reduce the sound level. In fact, placing the barrier at a certain angle can be more effective in reducing sound levels.

To calculate the SPL at the rear façade of your property when the barrier is in position, we can use the same equation as before, but this time we will use the distance from the noise source to the barrier (let's call it r2) as the reference distance. So the equation becomes:

SPL = 85 - 20*log(45/r2)

To find the best position for the barrier, we need to find the value of r2 that gives us the lowest SPL. This can be done through trial and error, or by using a computer program that can plot the SPL as a function of r2.

Once you have found the value of r2 that gives you the