Download Acoustics7

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Arch 353
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Dr. Abdelrahman Elbakheit
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References
1. ‫ سعود صادق حسن‬.‫ د‬, ‫الصوتيات‬
ِAcoustics
Noise control Basics and Fundamentals:
Noise is one of the factors of Environmental Pollution……Acoustical Pollution.
Noise increases directly/indirectly by Plant use, transportations and other
activities in Modern cities.
The main aim is provide a reasonable level of quietness for a given space either
indoors or outdoors
Noise Definition:
Noise can be defined as the unwanted sound/ Sounds.
From this definition we can regard that speech and music can be noise as well.
Factors affecting noise definition:
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Sound Loudness. Can be a noise source.
Frequency. High frequencies can be a noise source.
Intermittent or chaotic sounds, can be a noise source.
Unidentified sound sources, can be a noise source.
Sound not-accompanying activities, can be a noise source.
Unexpected Sounds, can be a noise source.
Personal Mood, mental or physical condition
Noise Level Consequences:
Noise can be detrimental in three main ways,
-Psychological side effects.
Annoyance, lake of concentration, lake of sleep, Nervousness, discontent
-Physiological side effects.
In digestion, Blood circulations problems, blood pressure, ear pains, loss of hearing
-Social side effects.
Increase of errors chances, lack of productivity.
Note: this does not mean that full silence is good or acceptable.
We can become accustomed to a certain level of noise psychologically but our
bodies can still be affected by it.
Noise metering:
Noise is measured by Sound Level Meters.
Normally have a sound weighting capability to match meters sensitivity to sound
level.
As well as having frequency analysers to break down sound into different
frequencies.
We came across how to add several sounds together by algorisms, this can be
also used to determine Noise Level.
Noise Criterion:
It is meant for the required effect from a certain activity. For instance if the activity was speech then
speech interference is the Criterion we will be looking for.
1.
Design Criterion:
when dealing with building design, we will not be dealing with high levels of Noise (i.e., 140150 db) as it causes immediate loss of hearing. This type of noise very rare in buildings. The
more common type of noise which depend on sound intensity and duration of occurrence is
more frequent in buildings such as factories and construction sites.
2.
Background Noise criterion:
Many studies have been conducted to determine the level of background noise for various types
of activities, such as in the following table.
3.
Speech interference level:
speech clarity depends on many factors, such as the level of background noise, distance
between the speaker and the listener, sound loudness and listener hearing capability.
normally speech interference happen at 1000,2000 and 4000Hz frequencies. Therefore
mean interfering sounds at these frequencies are calculated and normally known as
Sound interference level.
to avoid Sound interference noises should be at a certain level.
4.
Dissatisfaction Criterion:
this criterion depends on both measurements and subjective responses, therefore the audience
satisfaction level would need to be determined.
in an example of this, a study to the Traffic Noise Index were conducted with 7 levels of
satisfaction from fully satisfied to totally not satisfied. The study resulted in a co-relation between
dissatisfaction and what is called the 10% rule.
that is when noise is happening 10% of the time the majority will feel not satisfied.
Noise Sources:
There are many sources for noise that can be classified as
Internal Sources:
Such as radios, televisions, music instruments, moving furniture, printers, Hoovers,
etc…
External Sources:
Such as Traffic and all travelling means, cars, planes, trans etc…
Noise transfer in Buildings:
Noise reaching recipients can be of three categories:
1.Noise generated and transferred through the air such as musical instruments.
2.Noise from impacts such as, feet, door slam etc…
3.Noise out of mechanical Vibrations.
This categorization is made because each type of these noise need a different way to
handle or stop. All reach the recipient by air as a final means of propagation but
their formation and combat is different.