building services- acoustics and lightning

1. BUILDING SERVICES
ACOUSTICS AND
LIGHTING

2. WHAT IS ACOUSTICS ?
Acoustics is defined as the science that deals with the production, control,
transmission, reception, and effects of sound (as defined by Merriam-Webster).
Many people mistakenly think that acoustics is strictly musical or architectural in
nature. While acoustics does include the study of musical instruments and
architectural spaces, it also covers a vast range of topics, including: noise control,
SONAR for submarine navigation, ultrasounds for medical imaging,
thermo acoustic refrigeration, seismology, bioacoustics, and electro acoustic
communication. Below is the so called "Lindsay's Wheel of Acoustics", created
by R. Bruce Lindsey in J. Acoust. Soc. Am. V. 36, p. 2242 (1964). This wheel
describes the scope of acoustics starting from the four broad fields of Earth
Sciences, Engineering, Life Sciences, and the Arts. The outer circle lists the
various disciplines one may study to prepare for a career in acoustics. The inner
circle lists the fields within acoustics that the various disciplines naturally lead to

3. WHAT IS VELOCITY ?
Velocity is a vector quantity that refers to "the rate at which an object
changes its position." Imagine a person moving rapidly - one step forward
and one step back - always returning to the original starting position. While
this might result in a frenzy of activity, it would result in a zero velocity.
Because the person always returns to the original position, the motion
would never result in a change in position. Since velocity is defined as the
rate at which the position changes, this motion results in zero velocity. If a
person in motion wishes to maximize their velocity, then that person must
make every effort to maximize the amount that they are displaced from
their original position. Every step must go into moving that person further
from where he or she started. For certain, the person should never change
directions and begin to return to the starting position.
WHAT IS FREQUENCY?
Frequency describes the
number of waves that
pass a fixed place in a
given amount of time.
So if the time it takes for
a wave to pass is is
1/2 second, the frequency
is 2 per second. If it takes
1/100 of an hour, the
frequency is 100 per
Hour.

4. SOUND INTENSITY
Sound intensity is defined as the sound power per unit area. The usual context is the
measurement of sound intensity in the air at a listener's location. The basic units
are watts/m2 or watts/cm2 . Many sound intensity measurements are made relative
to a standard threshold of hearing intensity I0
The most common approach to sound intensity measurement is to use
the decibelscale
Decibels measure the ratio of a given intensity I to the threshold of hearing intensity
so that this threshold takes the value 0 decibels (0 dB). To assess sound loudness,
as distinct from an objective intensity measurement, the sensitivity of the ear must
be factored in.
VARIOUS TYPES OF SOUND ABSORBENT MATERIALS?
Sound Absorbent Materials can be incorporated in building structures either in
compressed state or in suspended state or in free state. In compressed state, they are
provided between the load bearing panels of ceiling and floor. In suspended state,
they are provided in the form of slabs fastened to ceiling so as to provide an air
space. In free state, they are provided in compressed or loose manner.
According to the nature of absorbing sound, the sound absorbent materials can be
classified as follows:
1. Porous Materials: This type includes lightweight concrete with porous
aggregate, foam glass, etc.
2. Porous cum elastic materials: This type includes porous materials with an
elastic backing.
3. Baffle Materials: This type includes thin panels from veneer, rigid wood
fibre slabs, solid cardboard etc.
4. Perforated Material: This type includes perforated panels and slabs. The
holes may be of equal diameter or different diameters and they may be
symmetrically arranged or located at random on the surface of panels or slabs.

5. Various types of absorbent materials are available in the market under different
trade names. The value of coefficient of absorption is supplied by the
manufacturer. Following are some of the common types of absorbent materials:
1. Hair felt: This material was used by Prof. Sabin in his experimental
works. The average value of coefficient of absorption of 25 mm thick hair felt is
0.60.
2. Acoustic Plaster: This is also known as fibrous plaster and it includes
granulated insulation material mixed with cement. If quantity of cement is more
than required, the plaster will not have sufficient pores to become effective for
acoustics. If quantity of cement is less, the plaster will not have enough strength.
Thus the quantity of cement should be carefully decided. For thickness of 20 mm
and density of 0.10 g / cubic centimeter, the acoustic plaster possesses an
absorbent coefficient of 0.3 at 500 cycles per second. Acoustic plasterboards are
also available. They can be fixed on the wall and their coefficients of absorption
vary from 0.15 to 0.30.
3. Acoustical Tiles: These are made in factory and sold under different trade
names. The absorption of sound is uniform from tile to tile and they can be fixed
easily. However, acoustical tiles are relatively costly than other absorbent
materials. They are most suitable for rooms in which small area is available for
acoustical treatment.
4. Strawboard: This material can also be used as absorbent material. With a
thickness of 13mm and density of 0.24 g/ cubic centimeters, it possesses a
coefficient of absorption of 0.30 at 500 cycles per second.
5. Pulp Boards: These are soft which are prepared from compressed pulp.
They are cheaper and can be fixed by ordinary paneling. The average value of
coefficient of absorption is 0.17.

6. 6. Compressed fiberboard: This material may be perforated or imperforated.
The average coefficient of absorption for the former is 0.30 and for the latter is
0.52. It has density of 0.30 g/ cubic centimeters.
7. Compressed wood particleboard: This material is provided with
perforations and it can be painted also. With a thickness of about 13mm, the
average coefficient of absorption is 0.40.
8. Perforated Plywood: This material can be used by forming composite
panels with mineral wool and cement asbestos or with mineral wool and
hardboard. It is generally suspended from trusses. The average value of
coefficient of absorption for the former composite panel is as high as 0.95 and
for latter composite panel, it is about 0.20.
9. Wood wool board: This material is generally used with a thickness of
25mm and it has a density of 0.40 g / cubic centimeter. The average value for
coefficient of absorption is 0.20.
10. Quilts and Mats: These are prepared from mineral wool or glass wool
and are fixed in the form of acoustic blankets. The absorption coefficients of
such quilts and mats depend on the thickness, density, perforations, mode of
fixing, nature of backing and frequency of sound.
WHAT IS SOUND TRANSMISSION?
As a sound wave travels across a room and touches a wall, a reflective wave is
produced that will reintroduce a portion of that wave back into the room. The
balance of the original sound will attempt to pass through the wall to the
adjoining room. The energy that survives this transfer is called Sound
Transmission. The energy that is returned to the original medium is
called Sound Reflection and is covered in its own course here at the Academy.

7. WHAT IS NOISE AND ITS EFFECT?
When one plays a musical instrument, say a guitar, the vibrating chords set air
particles into vibration. The vibration of air particles produces sound.
Noise is unwanted sound. Noise can be produced by many sources - man's vocal
cord, a running engine, a vibrating loudspeaker diaphragm, an operating machine
tool, and so on. Click on the demo buttons and you will hear the noise from
different sources.
There are two important characteristics of sound or noise - frequency and loudness.
Sound is the quickly varying pressure wave travelling through a medium. When
sound travels through air, the atmospheric pressure varies periodically. The number
of pressure variations per second is called the frequency of sound, and is measured
in Hertz (Hz) which is defined as cycles per second. The higher the frequency, the
more high-pitched a sound is perceived. The sounds produced by drums have much
lower frequencies than those produced by a whistle, as shown in the following
diagrams. Please click on the demo button to hear their sounds and the difference in
pitch.
The response of the human ear to sound is dependent on the frequency of the
sound. The human ear has peak response around 2,500 to 3,000 Hz and has a
relatively low response at low frequencies. Another property of sound or noise is its
loudness. A loud noise usually has a larger pressure variation and a weak one has a
smaller pressure variation. Pressure and pressure variations are expressed in Pascal
(Pa). To express sound or noise in terms of Pa is quite inconvenient because we
have to deal with numbers from as small as 20 to as big as 2,000,000,000. A
simpler way is to use a logarithmic scale. As such, the loudness of sound is
commonly expressed in decibel (dB).

8. EFFECTS OF NOISE POLLUTION
1. Hearing Problems: Any unwanted sound that our ears have not been built to
filter can cause problems within the body. Our ears can take in a certain range of
sounds without getting damaged. Man made noises such as jackhammers, horns,
machinery, airplanes and even vehicles can be too loud for our hearing range.
Constant exposure to loud levels of noise can easily result in the damage of our
ear drums and loss of hearing. It also reduces our sensitivity to sounds that our
ears pick up unconsciously to regulate our body’s rhythm.
2. Health Issues: Excessive noise pollution in working areas such as offices,
construction sites, bars and even in our homes can influence psychological health.
Studies show that the occurrence of aggressive behavior, disturbance of sleep,
constant stress, fatigue and hypertension can be linked to excessive noise levels.
These in turn can cause more severe and chronic health issues later in life.
3. Sleeping Disorders: Loud noise can certainly hamper your sleeping pattern
and may lead to irritation and uncomfortable situations. Without a good night
sleep, it may lead to problems related to fatigue and your performance may go
down in office as well as at home. It is therefore recommended to take a sound
sleep to give your body proper rest.
4. Cardiovascular Issues: Blood pressure levels, cardio-vascular disease and
stress related heart problems are on the rise. Studies suggest that high intensity
noise causes high blood pressure and increases heart beat rate as it disrupts the
normal blood flow. Bringing them to a manageable level depends on our
understanding noise pollution and how we tackle it.

9. 5. Trouble Communicating: High decibel noise can put trouble and may not
allow two people to communicate freely. This may lead to misunderstanding
and you may get difficult understanding the other person. Constant sharp noise
can give you severe headache and disturb your emotional balance.
6. Effect on Wildlife: Wildlife faces far more problems than humans because
noise pollution since they are more dependent on sound. Animals develop a
better sense of hearing than us since their survival depends on it. The ill effects
of excessive noise begin at home. Pets react more aggressively in households
where there is constant noise.