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