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A barrier can be considered to be any solid obstacle which impedes the line of sight between
source and receiver thus creating a sound shadow. In this program the attenuation of sound energy by an
environmental barrier is calculated using the Kurze-Anderson formula:
When
LB =
attenuation (dB) due to the barrier obstruction. N
is the Fresnel number ( N > 0.2 and N< 12.5).
The calculation of N is shown below, where λ is the wavelength and f is
the frequency. For
N> 12.5, experimental data show that there is an upper limit of 24 dB.
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A noise barrier is only
effective if it is large compared to the wavelength of the sound -- in
other cases diffraction effects render it virtually transparent, therefore
it must extend laterally sufficiently far to prevent diffraction occurring
around the ends; the barrier length should be such that the distance from
the source to the ends is at least twice the normal
distance of the source to the barrier; or a barrier coders an angle of
160˚subtended from the receiver; or the barrier length should be more than
4-5 times of the height. The source and receiver
positions can be strategically arranged, as shown below.
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[source: Kurze, U. J. and
Anderson, G. S., 1971, Sound attenuation by barriers. Applied Acoustics, 4,
35-53]
Clickhere to start calculation.
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This program
calculates sound level distribution and reverberation in rectangular urban
streets canyons with geometrically reflecting boundaries. The program is
based on the image source method. Using the program the effects of basic
street parameters can be analysed.For both sound level and reverberation calculation, the program allows the
following inputs:
(1) Street length (x), width (y) and height (z).
(2) Sound source position.
(3) The height of a horizontal receiver plane, where there are 10
(width) x 10 (length) calculation points.
(4) Sound absorption coefficient of facades and ground. Air absorption (Np/m)
can also be input. Typical air absorption values can be selected.
(5) For sound pressure level calculation, source pressure level at 1m
from the source.
Clickhere to start calculation.
For further information and algorithm, please see
here.
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This program calculates absorption coefficient of micro-perforated panels and
membranes mounted over an airtight cavity. Using the program a
required absorber can be designed, and the effects of various parameters can
be demonstrated.
For comparison, two
configurations, one with a single layer and one with double layers, can be
considered. Sound incident angle can also be specified.
Basic sound absorbers
include porous absorbers, single resonators, perforated panel absorbers, and
panel and membrane absorbers. The perforated panel absorbers are more
commonly used in practise. |
Micro-perforated absorber is a newly developed sound
absorber, it has a number of attractive features:
- Unlike conventional perforated absorbers, micro-perforated absorber can be
made from transparent materials like plastic glass.
- Unlike commonly used fibrous absorptive materials, micro-perforated
absorber is fibrous-free and thus, there is no health concern.
- Micro-perforated membranes are lightweight and inexpensive.
The absorption performance of micro-perforated absorber is very good.
Typically the absorption coefficient exceeds 0.4 over 3-5 octaves.
This calculation depends
on the following parameter inputs:
1. Panel thickness
2. Aperture diameter
3. Aperture spacing
4. Air-space depth
5. Material (PVC or Metal)
6. Angle of sound incidence
7. Acoustic resistance of the membrane (normally 1 can be used)
8. Surface density of the membrane
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Clickhere to start calculation.
For further information and algorithm, please see
here.
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Reverberation time is the time
taken for a sound to decay 60dB after the source is stopped , it is the most
important index of reverberation. During calculating, input parameters
needed are room dimensions and boundary absorption coefficients. A database of
absorption coefficients is given, including the most common
materials in room acoustics. The Eyring formulae is used as a modification
of the Sabine formula:
V - volume
of the room(m3)
S - total surface area of
the room (m2)
ā - average absorption
coefficient of all the boundaries
m - air absorption coefficient
It is important to note that Eyring formulae embody the assumption of a
diffuse field space. Although there is no real sound field that strictly meets
this condition, the formulae is accurate enough for many enclosures.
Clickhere to start calculation.
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This is a computer tool which allows users to input idealised urban streets and
squares in a 2D environment. After selecting and
positioning a number of urban sound
sources, the soundscape file with multiple sources can be played back, with reverberation
effects.
Clickhere to start calculation.
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