What is the difference between this two pictures

Project 2 Measurement and analysis of environmental parameters Lighting - Measurements - Calculation Thermal comfort in ECJ classroom Noise measurement Report Daily oscillation measurement (HOBO)

Objectives Learn about basic acoustic in buildings Noise 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 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 20-20KHz 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 Control 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 Gypsum board Insulation blanket 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