NATIONAL UNIVERSITY OF

SCIENCE & TECHNOLOGY

FACULTY OF THE BUILT

ENVIRONMENT

DEPARTMENT OF ARCHITECTURE

An Environmental Design Assignment Second Year, 2012-2013, Semester 2

Environmental Design II AAR 2204 Lecturer: Mr. Nyamande

1st Year Design Studio Acoustical Calculations By Group: Blessing Mukome (N0113440P) Nothabo Ndlovu (N01110491L) Bryan Faranando (N0110286Y)

1

Introduction The purpose of the exercise is to evaluate the acoustical effects of the materials used in

the Part 1 Design Studio by calculating the reverberation time of the room and checking

whether or not the room is suitable for its current use as a design studio. Illustrations of

the space in the form of a floor plan and pictures have also been added.

Name of space:

Part 1 Design Studio

Current function/use of space:

The space is currently being used as a design studio and class room for the first year

architecture students.

Intended function/use of space:

The space was designed to serve as office space for the university.

Size of space:

Length of room: 11540mm (clear distance)

Width of room: 6700mm (clear distance)

Height of room: approx. 2900mm

Floor area = length × width

= 11.54m × 6.7m

= 77.32m2

Volume of room = floor area × room height

= 77.32m2 × 2.9m

= 224.22m3

Estimated occupancy of space:

Deducing from observation of current use of the space, it’s current average occupancy

is 25 users.

2

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3

Image showing column, glazing and the aluminum framing in the studio

Image showing ceiling and luminaire layout (5 by 3 configuration)

4

Analysis of Materials

Material Quantity Area/Unit

(m2) Total Area (m2)

αs at 125Hz

Sα at 125Hz

αs at 4KHz

Sα at 4KHz

Furniture

Drawing boards (vanished wood)

10 1.02 10.2 0.19 1.94 0.3 3.06

Stools/seats (wood) 10 0.12 1.23 0.15 0.18 0.3 2.4

Model making tables (wood)

2 2.19 4.38 0.19 0.83 0.3 1.31

Whiteboard (porcelain) 1 2.07 2.07 1.69 3.50 1.42 2.94

Storage drawers (steel) 1 2.94 2.94 0.15 0.44 0.19 0.56

Ceiling Materials

Suspended ceiling (acoustic tiles; perforated steel)

294 0.25 73.57 0.05 3.68 0.32 23.54

Luminaires (aluminum reflecting surface)

15 0.25 3.75 0.38 1.43 0.87 3.26

Floor Materials

Floor finish (ceramic tiles)

- - 77.32 0.01 0.77 0.02 1.55

Wall Materials

Wallpaper on brick wall - - 12.915 0.02 0.26 0.08 1.03

Plastered brick wall - - 20.1 0.013 0.26 0.05 1.01

Timber partition wall - - 18.6 0.25 4.65 0.1 1.86

Window frame (aluminium 50mm cavity)

- - 6.6 0.38 2.51 0.87 5.74

Column (wallpaper on concrete)

- - 5.7 0.02 0.11 0.08 0.46

Window panes (glass) 51 0.88 45.06 0.35 15.77 0.04 1.80

Door glass panels 6 0.76 4.58 0.35 1.60 0.04 0.18

People 25 - 25 0.25 6.25 0.5 12.50

TOTAL Sα 44.19 63.20

5

Perforated steel (on ceiling)

Metal is a good sound reflector, and as such, the material on the ceiling reflects sound

back into the room. However, some of the sound is absorbed due to the perforations in

the material.

Glazing

Glazed areas are both the structurally and acoustically weak areas on a building shell,

but they can be made to be good sound absorbers when treated well to provide

insulation. The type of glass used for the first year studio – laminated glass – is a good

sound absorber; and it’s fixation to the aluminum framing with the use of rubber sealing

further adds to the sound absorption quality, as well as helping in containing sound

within the room.

Aluminum Framing

Aluminum has metal properties, and thus is a sound reflector.

Wallpaper (on brick walls and column)

Wallpaper is generally a good sound absorber – but the background on which it is fixed

onto (brick and/or concrete) reflect sound.

Timber (used on the partition wall and furniture)

Timber makes for a good sound reflector – as shown by its extensive use in acoustical

spaces. Most of the furniture in the first year studio is made mostly from plywood.

Ceramic tiles (used as floor finish)

Ceramic tiles are made of hard material, which produces sounds due to vibrations;

therefore movement of objects such as furniture makes the room noisy. Also, ceramic

material is a sound reflector, which contributes to the noise as sounds made are

reflected back into the room. Sound absorption is aided by the grout (which has sound

proof properties) which is used to fix the tiles onto the floor.

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Calculations

Reverberation Time

The reverberation time ( ) is defined as the length of time required for sound to decay

or fall in level by 60 decibels (60dB) from its initial level. Classrooms should have

reverberation times in the range of 0.4-0.6 seconds, but many existing classrooms have

reverberation times of 1 second or more. In such cases, the teacher is competing

against the lingering reflections of his or her own voice for the student's attention. The

result is a chaotic jumble of sounds.

The table above shows the optimum reverberation times for speech and music, for a

recommended minimum volume of auditoria. Given that our room has a volume of

224.22m3, the expected reverberation time for speech should be less than 0.7 seconds.

The reverberation time can be calculated by using an equation developed by Harvard

physics professor named Wallace Clement Sabine:

Sabine’s Formula

Reverberation time,

Where : V = room volume in m3

Sα = total surface absorption in m2

x is a coefficient related to the sound attenuation of air

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Given that the value x is not provided; an empirical formula for calculating reverberation

time is used:

Reverberation time,

The total surface absorption (Sα) is obtained by adding together the separate areas of

absorbent:

From the table of materials:

Sα at 125Hz = 44.19m2

Sα at 4kHz = 63.20m2

Reverberation time at 125Hz (low frequency/pitch sound):

A RT of 0.81 seconds implies that it takes 0.81 seconds for interrupted sound to decrease by

60dB, given a sound intensity/frequency of 125Hz. This is outside the optimum 0.4 – 0.6

seconds required for a classroom environment, but sound reflective (echo) effects may not be

as significant.

Reverberation time at 4kHz (high frequency/pitch sound):

A RT of 0.56 seconds implies that it takes 0.56 seconds for interrupted sound to decrease by

60dB, given a sound intensity/frequency of 4kHz. This is within the optimum 0.4 – 0.6 seconds

required for a classroom environment, which means that speech audio will be quite audible in

this environment.

In conclusion, the space being studied is relatively suitable for its current use, than not.

8

Sources

http://www.sengpielaudio.com/calculator-RT60Coeff.htm

http://www.engineeringtoolbox.com/accoustic-sound-absorption-d_68.html

http://www2.ibp.fraunhofer.de/akustik/ra/owa/index_e.html

http://www-958.ibm.com/software/data/cognos/manyeyes/datasets/sound-

absorption-coefficients/versions/1

http://www.bembook.ibpsa.us/index.php?title=Absorption_Coefficient

http://goodinsulationmaterials.blogspot.com/2012/01/aluminium-sound-absorption-

panel.html

http://www.bentonbrotherssolutions.com/aluminum-frame.htm

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Appendix

Tables of (sound) absorption coefficients of materials

10

11

11.5

40

0.78

0

0.79

0

0.76

51.

970

0.40

0

0.5006.700

AA

B B

Modelmakingtable

Modelmakingtable

A1paper

cabinet

Drawingboards

Dean'sOffice

GraduateStudio

1st Year Design Studio(ceramic tiles)

FLOOR PLANScale 1:50

Cove

red

Wal

kway

2900

mm

hea

droo

m h

eigh

t

11.540

Timberboard

partitionwall

Concrete slab

SECTION A-AScale 1:50

Wallpaperon brick wall

Glazingpanels onaluminium

frameGlass

panelleddoor

2900

mm

hea

droo

m h

eigh

t

6.700

Suspended ceiling(perforated steel)

(400 x 500)mmconcretecolumn withwallpaper finish

SECTION B-BScale 1:50

Whiteboardmarker

Wallpaper onbrick wall