ME 458 Lab 8 8/17/2000 page 1
ME 458 Noise Control
Laboratory #8
Barriers
Objectives:
1. Experimentally determine the effectiveness of a noise barrier.
2. Compare to theoretical predictions
Background: Sound barriers (i.e. walls) are a common noise control measure,
particularly for outdoor noise problems. A simple calculation procedure for the excess
attenuation of a long barrier, developed by Z. Maekawa, is:
A
ABd
EBARRIER =+≥
±+−
20 2
25log tanh
()
π
π
λ
Ν
Ν dB for N -0.2
N = 2 ( Fresnel Number)
where + sign indicates receiver in the shadow zone
- sign indicates receiver in the "bright" zone
The objective of this experiment is to
gather empirical data to verify
(hopefully) this relationship. The basic
equation to quantify propagation in a
free-field is:
LL r A
Apw E
E
=− − −
=
20 10 83log .
Excess attenuation due to all effects including ground
reflection , barriers, atmospheric absorption , etc
Procedure:
1. Use the large speaker, power amplifier and random noise generator to provide a
repeatable noise source. Quantify the sound power of the source in each octave
band by measurements close to the source without the barrier in place. Measure the
sound levels with a sound level meter.
2. Place the barrier (two 4'x8' plywood sheets) approximately in the center of the
anechoic room (or outside if the weather is warm enough). Measure the sound
levels on the other side of the barrier from the sound source.
3. Calculate the excess attenuation due to the barrier
