What is the difference between this two pictures

Project 2 Measurement and analysis of environmental parameters a) Lighting - Measurements - Calculation b) c) d) e) Thermal comfort in ECJ classroom Noise measurement Report 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_cfrc 040. . .

Octave band frequency • Sound 15 Hz – 15 k. Hz • Human conversation 100 Hz – 6 k. Hz • Octave frequencies 8, 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 -20 KHz • most sensitive 3 KHz • amplitude - magnitude of pressure variation (pmax - pmin)

Decibel • Sound Pressure Level - SPL= 10 log(p/pref)2 [ d. B] p – air vibration pressure – sound pref - reference pressure (20 μPa or 10 -9 psi) Speed of sound c=340 m/s Example:

General perception of sound

Sound Perception • 120 d. B - 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 d. B

Adding decibel quantities • d. B=10 log x • 2 equal sources d. B= 10 log (x+x) =10 log(2 x) =10 log(2) +10 log(x) = 10 log(x) + 3 • n equal sources d. B= 10 logx+10 log(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 d. B after sound source has stopped producing sound

Sound control by Absorption Convoluted Egg Crate Acoustical Foam

Noise Sources in HVAC System

Noise 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 Insulation blanket Gypsum board Frame (stud) Damped Resilient Channel Gasket www. asc-soundproof. com/iso-diagrams. htm

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