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What is the difference between this two pictures
Project 2
Measurement and analysis of environmental parameters
a) Lighting - Measurements- Calculation
b) Thermal comfort in ECJ classroom c) Noise measurement d) Report e) Daily oscillation measurement (HOBO)
Objectives
• Learn about basic acoustic in buildings • Phenomena• Terminology
• Noise• Quantities• Sources in building• Reduction techniques
Sound –air pressure oscillation
Amplitude
Frequency of Sound
www.trentu.ca/trentradio/audiosoup/as_cfrc040...
Octave band frequency
• Sound
15 Hz – 15 kHz
• Human conversation
100 Hz – 6 kHz
• Octave frequencies8, 16, 32, 63, 125, 250, …. Hz
NOISE
• Usually defined as "unwanted sound“
• Sound waves described by following parameters:
• frequency • human ear can hear between 20-20KHz• most sensitive 3 KHz
• amplitude - magnitude of pressure variation (pmax - pmin)
Decibel
• Sound Pressure Level - SPL
SPL= 10 log(p/pref)2 [ dB]
p – air vibration pressure – sound
pref - reference pressure (20 μPa or 10-9psi)
Speed of sound c=340 m/s
Example:
General perception of sound
Sound Perception
• 120 dB - Pain limit
Noise Criteria - NC
• Define acceptable background noise spectra
• Defined for octave band 63 Hz – 8000 Hz
• Generally
NC = A weighted noise level – 5 dB
Adding decibel quantities
• dB=10 log x
• 2 equal sources
dB= 10 log (x+x) =10 log(2x) =10log(2) +10log(x)
= 10log(x) + 3
• n equal sources
dB= 10logx+10log(n)
Acoustic in a building
• Every element of building design and construction affects its acoustical characteristics
• Acoustic principles should influence • choice of finish materials in rooms, • location of these materials in a building, • building design.
Room acoustic
• Behavior of Sound in an Enclosed Space• shape• dimensions • construction
• Major sources of absorption/reflection in a room:• Ceiling • Floor • Furniture
Factors Influencing Acoustical Environments
• How is space to be used? e.g. office, hospital, theater, auditorium, library
reading room
• Type of noise sources? voice, music, impact sounds.
• Predictability of source? expected sounds less stressful than unexpected sound.
Parameters which define Acoustical Environments
• Sound absorbing/reflecting qualities of interior surfaces.
• Reflection time - echoes vs. "dead" space
• Source location/locations
• Receiver characteristics/expectations
Sound reflection and absorption
• Absorbed sound is turned into heat energy
• Absorption coefficient ()• ratio between absorption of a material and open window
• = 1.0 all sound energy is absorbed
• Reflection - Echo • persistence of sound after it has stopped - echoes
• Reflection Time (Tr)
period required for sound level to decrease 60 dB after sound
source has stopped producing sound
Sound control by Absorption
Convoluted Egg Crate Acoustical Foam
Noise Sources in HVAC System
Noise ControlNoise Control for Roof Top HVAC Equipment
Noise Control
• Duct silencers- Absorptive- Dissipative
Use sound absorptive material
Noise Control
• Elastic connections• Ducts – fans• Pipes - pumps
Active Noise Silencer
www.appliedsignalprocessing.com/hvacapp.htm
Wall sound insulation
www.asc-soundproof.com/iso-diagrams.htm
Frame
(stud)
Gypsum boardInsulation blanket
Damped Resilient
ChannelGasket
Wall sound reduction as function of Frequency
• Low frequency sound - More difficult to reduce
- Damped Resilient Channel
• High frequency sound - Can be reduced easier with sound insulation
materials such as fiberglass
Wall Absorption
Window Sound Insulation
Glazing
Frame
Gaps
More about Acoustics
Tao and Janis
Chapter 18 and section 18.1 - 18.18