The common plumbing system noise sources is water flowing through pipes and noise radiating from the walls of pipes.

1. ADDIS COLLEGE
Department of Architecture and Urban
Planning
Course: ARCHITECTURAL SCIENCE IV-
ACOUSTICS
Group Members
Names ID.No
1.Samuel Seyoum 053/12
2.Surafel Temesgen 158/12
3.Tesfawork Getye 243/12
4.Usman Amir 364/12
5.Yoseph Bete 010/12

2. Plumbing Noise and Its Control
Img.1.1.Cross sections of sealed wall
penetrations with duct and a pipe
 The common plumbing system noise sources
is water flowing through pipes and noise
radiating from the walls of pipes.
 That noise in ducts is produced due to abrupt
direction change (dog legged turn) and cross
sectional change (transition).
 For plumbing systems we are dealing with
liquid flow so its basically dealing with ducted
systems and pipes can be wrapped with
lagging materials to reduce breakout noise
radiated from the pipe walls.

3. Mechanical Equipment Rooms and Sound Isolation
A property mounted spring isolator
Examples of misaligned and misloaded
spring isolators
-The sound a machine produces:
 Direct sound (air Borne)
Sound Isolation
 Vibratory (impact, flanking):- this can travel
through a building’s structural members to affect
remote locations within a building. It is therefore
prudent to isolate any heavy equipment from any
structural members of buildings.
 Can be accomplished by mounting the
equipment on springs, pads, and/or inertia
blocks; however, the selection of specific isolating
devices (especially springs) should be performed
by a specialist trained in vibration analysis.
 The key here is to eliminate any rigid connections
between the units and the structure.
Pipe supports rigidly attached to a
structural floor. Channeling vibrations
throughout the building structure.

4. HVAC Systems
Img.1.2.Cross section of a double layer
gypsum-board duct enclosure.
There are two general categories when it comes to
HVAC system noises and they are: mechanical
equipment and duct-borne/airflow noises.
Mechanical Equipment: includes pumps,
compressors, chillers, generators, and air handlers.
-Rotating components such as gears and fans,
generate most of the noise that causes concerns in
buildings.
-Besides noise they also generate vibrations that can
excite building members far from the sources and
cause remote building components to rattle and
generate their own noise.
Duct-borne/airflow When air is carried throughout a
building using ductwork , fans are needed to
generate the flow causing noise by inducing
turbulence in the airflow.
-This noise is either carried through the ductwork
into rooms or its directly radiated from the duct
walls (known as breakout noise).

5. Noise Control during Construction
Acoustical Treatment
Is usually applied to existing structures with defective acoustics or when there is a functional
change to the room. The treatments range from Sound Lobby introduction, Opening redesign
to Surface treatment. This allows for the creation of quiet environment that is suited to the
function of the space.
construction noise is highly disruptive to the surrounding. To avoid creating such
environment remedial steps taken are:
 Care in applying the design, good control
and supervision
 Less noisy construction activity
 Prefabs (blocks to elements) instead of on-
site production
 Less noisy machineries
 Not to work during night times
 To work at ground level (assemble) and fix
on upper floors.

6. Acceptable Noise Levels
Note
Sound levels expressed in decibels are not necessarily an indication of how loud sounds will
seem to the human ear. The sensitivity of the ear depends mostly on frequencies the
intensity of sound being compared.

7.  Check List for Acoustic Work
1. Identify noise sources/
community noise, near, inside
2. Check the level of noise/
acceptable or not/
3. First stage solution – by planning
4. Design of volume separation,
sound lobbies etc..
5. Using sound insulation
mechanism or treatment.
 Specifying in Acoustical Design
 Acoustical specification (for acoustical products and
construction work) Includes:
 Material type and quality
 Thickness
 Technique of construction
 Acoustical performance with sound absorption and Noise
reduction levels.
Note
The performance data is usually available in industrial product
catalogue which are prepared based on standard tests.

8. Room Acoustics
Room Acoustics Objective:
• Providing the best condition for both production &
reception of desirable sound
Room Acoustics Considerations:
• Reverberant field / Enclosure
• Satisfactory distribution of sound
• Exclusion of unwanted sound /Noise
Pattern of Distribution of Sound in an Enclosure
• Sound path: can be generally defined as the
distance and direction sound travels during
propagation.
• The distribution and decay of sound energy in an
enclosure depends mainly on the nature of interior
materials, roughness, smoothness, porosity,
hardness and the angle of the surfaces.
 Room Acoustics main concern is the control of sound within an enclosed
space and creating suitable interior acoustic environment.

9. Ray Diagram Analysis
Limitations
1. Sound reflects in the manner
indicated by ray diagrams only when
surface dimensions are relative to
the wavelength of the sound being
evaluated.
2. It radiates from different position.
Different balance of sound
distribution from several source
positions to the listening area.
3. Detailed evaluation of diffusion of
sound by room surfaces is not
possible with ray diagrams.
• For a relatively accurate acoustic
modeling, scaled models which allow
frequency called acoustical studies are
used especially where the acoustic
perception is important.
Ray diagram is an acoustical
analogy to peculiar (mirror like)
reflection of light where the
angle of incidence (T) equals the
angle of reflection (f) with
angles measured from the
perpendicular to the surface.
• The patterns of distribution of sound are easily analyzed by ray diagram
(geometrical optics).

10. Diffusion: is the scattering or random redistribution of a sound wave from a surface.
 It occurs when the surface depths of hard-surfaced materials are comparable to the
wavelengths of the sound.
 It does not "break up" or absorb sound-sound is not fragile or brittle! However, the direction
of the incident sound wave is changed as it strikes a sound-diffusing material.
 It is an extremely important characteristic of rooms used for musical performances. When
satisfactory diffusion has been achieved, listeners will have the sensation of sound, coming
from all directions at equal levels.
Direct and Reflected Sound, Multiple Reflection
Reflection: is the return of a sound wave from a surface. If the surface dimension is larger than
about 2 to 4 times the wavelength A of the impinging sound wave, the angle of incidence will
equal the angle of reflection.
-When an array of suspended panels is used to direct reflected sound energy toward the
audience, the individual panels should be of varying sizes to prevent creating a "rasping" sound.

11. Diffraction: is the bending or "flowing" of a sound wave around an object or through an opening.
-For example;- a truck located behind a building can be heard
because the sound waves bend around the corners.
 In auditoriums, because impinging sound waves will readily
diffract around panels that are smaller than their
wavelength, suspended panels must be carefully designed
to be large enough (length and width) to effectively reflect
the desired wave length of sound.
 A single frequency can be emphasized called diffraction
grating effect when an array of small overhead panels are
of equal length and width or vertical projecting slats on
walls are of equal depth and spacing. This phenomenon
must be avoided because it can impart an odd tonal
distortion to music due to cancellation effects.

12. Absorption: is a reduction in the sound energy reflected from a surface. It is a major factor in
producing good room acoustics, especially when controlling reverberation.
The effective absorption of a particular surface depends on both the absorption coefficient of the
surface material and the area of that particular surface exposed to the sound.
Absorption of surface = area of surface x absorption coefficient of that surface.
Unit: m2 Sabin’s or ‘absorption units’
Total absorption = L (area x absorption coefficient)
Types of absorbers
 Panel/ membrane are absorbers for lower frequencies- 40-400Hz.
 Cavity absorbers are volume resonators for specific lower frequencies.
 Practical absorber- combination of several methods.
E.g. Acoustic tiles- the basic material of the tile, such as fiberboard, is porous and acts as an
absorbent for higher frequencies. The tile material may also be drilled with holes which then act
as cavity absorbers.

13. Reverberation Control: reduction of reverberant sound energy to
improve speech intelligibility and source localization.
Sound Level Control: reduction of sound or noise buildup in a room to
maintain appropriate listening levels and improve sound isolation to
nearby spaces.
Echo and Reflection Control: elimination of perceived single echoes,
multiple flutter echoes, or unwanted sound reflections from room
surfaces.
Diffusion Enhancement: mixing of sound in a room by alternating
sound absorptive and sound reflective materials.
 Absorptive surfaces be any of three basic types of materials:
1.Porous materials include fibrous materials, foam, carpet, acoustic
ceiling tile, and draperies that convert sound energy into heat by
friction. Example: fabric-covered 1 in. (2.5 cm) thick fiberglass
insulation panels mounted on a wall or ceiling.
2.Vibrating panels thin sound-reflective materials rigidly or resiliently
mounted over an airspace that dissipates sound energy by converting
it first to vibrational energy. Example: a 1/4 in. (6 mm) plywood sheet
over an airspace (with or without fibrous materials in the airspace).
3.Volume resonators :materials containing openings leading to a
hollow cavity in which sound energy is dissipated. Example: slotted
concrete blocks (with or without fibrous materials in the cores).
Absorptive surfaces are primarily used for the following applications:

14. Distribution and Decay of Sound Energy
Nature of interior surfaces characterized by porosity, smoothness, being reflective or absorptive
and Angle of the interior surfaces like walls and ceilings are responsible for the distribution and
decay of sound energy in the interior. Reflectors near the source properly distribute the sound
energy while absorbers significantly reduce or kill the sound energy.
Reflecting Surfaces and Pattern of Reflected Sound
Sound Reflectors
An effective sound reflector has a hard surface, such as thick plaster, double-layered gypsum
board, sealed wood, or acrylic plastic, and is significantly larger than the wavelength of sound it is
designed to reflect.
Section View of Church
In the church example shown the organ and console are located
within the sanctuary, not in a gallery or other deep recess.

15.  Reflectors in order of increasing effectiveness for distributing sound are concave, flat, and
convex sound-reflecting surfaces.
1.Reflection from plane surfaces
-This figure illustrates the geometry of sound
reflections from a flat, smooth surface.
The reflected sound waves are spherical and their
center of curvature is the ‘image’ of the source of
sound. The image is on a line normal to the surface
and at the distance from the surface as the source.
It will be seen therefore that the reflected sound will
attenuate at the same rate as sound in a free field,
that is, in accordance with the inverse square Law,
the intensity of the reflected sound waves will
therefore depend on their distance from the image
and the degree of absorption occurring at the
reflecting surface.
Flat Reflectors as building elements
Flat, hard-surfaced building elements, if
large enough and oriented properly, can
effectively distribute reflected sound. The
reflector shown below is tilted slightly to
project sound energy toward the rear of an
auditorium.

16. 2.Reflection from curved surfaces
-The geometry of reflection from curved
surfaces is best derived from the employment
of sound ‘rays’, an example of a sound ray
shown in the figure, and it can be defined as the
direction of propagation of the sound wave.
-The first drawing in the figure shows that a
reflected sound ray is on a radial from the
image in the case of a flat surface. The angle of
reflection of the ray is equal to the angle of
incidence to the surface.
-The second drawing in the figure shows that
rays striking a curved surface are each reflected
so that the angle of reflection is equal to the
angle of incidence to radials drawn at their
points of contact. Each ray will in effect have its
own image; the wave front will not be part of a
circle and must be found by drawing each ray of
equal total length as shown.
These figures make a direct comparison
between the reflections from flat, convex and
concave surfaces.
-The distance from the source to the reflector
is the same in each case, the cone of sound
considered is the same, and the time interval
at which the wave fronts are drawn is also the
same.
Concave and Convex Reflector as building
elements
-Convex, hard-surfaced building elements, if
large enough, can be most effective as sound-
distributing forms.
-Concave sound-reflecting surfaces (such as
barrel-vaulted ceilings in churches and curved
rear walls in auditoriums) can focus sound,
causing hot spots and echoes in the audience
seating area.

17. 3.Reflection of limited size
For effective sound reflection to occur a reflector must be large in relation to the wavelength of
the sound and, in all cases, the power of the reflected sound will be affected by diffraction at the
edges of the reflector.
Figure below shows sound waves reflected from reflectors of different widths together with the
diffracted waves (or wave fringes) which develop from the edges of the reflectors. The frequency
of the sound is the same in both cases, as indicated by wavelength, and therefore the degree of
diffraction is also similar.
However, in both cases, the energy in the diffracted sound waves is being extracted from the
main reflected waves and, because the latter are smaller in the second example, the effect of
this loss will be greater.
For a given frequency therefore small reflectors are less efficient than large ones. When
reflectors are used in auditoria to reinforce sound they must therefore be of adequate size.
Nevertheless, since the intelligibility of speech is much more dependent on hearing the middle
and high frequencies than on the reception of low frequencies, reflectors of about five times the
wavelength of middle frequencies (about 3m) are very effective in reinforcing speech sounds.

18. 4.Reflections form re-entrant angles
Sound entering a right-angled corner of a room will be reflected back towards the source if the
adjacent surfaces are of a reflective material. This is shown in the figure below. Such reflections
are often the case of Disturbing echoes.
As in case of all reflections, the phenomenon is frequency dependent, that is, related to
wavelength and the dimensions of the reflecting surfaces. Quite small areas of reflecting material
in the corner of a room, for example between ceiling and wall, can, however, result in high-
frequency echoes.
To prevent this return of sound towards the source the corner can, however, be modified in any
of the three ways as shown in the figure above
A) It may be other than a right angle
B) One surface may be made absorbent, or
C) One Surface may be made Dispersive.
Absorbent or dispersive treatment, if employed for this purpose, must, however, be taken right
into the corner, as shown.

19. Useful Reflections and Sound Reinforcement
Useful reflections
Useful reflections are found near the source, which are termed as early reflections. Useful sound
reflections come from the same direction as the one coming from the source have generally a
delay of less than 30m.s. (milliseconds).
Lateral reflections are early sound reflections from side walls can add strength to the direct
sound. Designing for strong early reflections can increase clarity, sound strength and
spaciousness.
Sound path in auditoriums
The initial-time-delay gap is the time interval between the arrival of the direct sound and the first
reflected sound of sufficient loudness. It should be less than about 30 ms (path difference
< 34 ft) for good listening conditions because sounds within this time interval can coalesce as one
impression in a listener's brain. Early-arriving reflected sound energy is important for clarity and
definition of music. "Early" sound is usually defined as the direct and reflected sound arriving
within the first 80 m s.
Clarity can be defined as the ratio of early sound energy to late or reverberant sound energy.
Auditoriums with narrow shapes support direct and early-reflected sound because the initial-
time-delay gaps will be short. In the design of auditoriums, ray diagrams can be used to
determine initial-time-delay gaps. The initial-time-delay gap also strongly influences a listener's
perception of the size of an auditorium (called intimacy).

20. Sound Paths from Stage in Auditorium
The listener in the auditorium will hear the direct sound first and then, after the initial-time-
delay gap, reflections from the walls (path 1 on the drawing), ceiling (path 2), stage enclosure
(path 3), and so on. These arrival times and sound levels are indicated by the bars on the sound
level vs. Time graph is shown below.
Sound Level vs. Time Graph for Auditorium

21. The effect of Room shape and Volume upon the quality of
sound
Side walls
Lateral reflections help create a favorable auditory spatial impression or intimacy. Early sound
reflections form side walls can add strength to the direct sound.
Rectangular shape
This shape is practical for seats under 1000 people. As long as reflectors are used over the sound
source the difficulty of obtaining sufficient loudness near the back can be overcome.
Fan shape
The audience is seated slightly closer to the sound source. It must be noted that the rear of such
fan shaped hall is not concave. Problems can arise from reflections from side walls