ACOUSTICS: branch of physics concerned with sounddeals with the production, control, transmission, reception, and effects of sound3 parts (elements):1. Sound Source ( e.g. human speech, HVAC equipment)2. Transmission Path (e.g. air, earth, building materials)3. Receiver (e.g. humans, animals, sensitive medical equipment)

physical wave in an elastic medium, usually air the sensation stimulated in the organs of hearing

by mechanical radiant energy transmitted as longitudinal pressure waves through the air or other medium

a vibration in an elastic medium such as air, water, most building materials, and the earth

physically, sound is a rapid fluctuation of air pressure

technology of designing spaces, structures and mechanical systems to meet hearing needs

effect of building design on the control of sound in buildings

3 Aspects of Acoustical Design in Buildings1. Planning to keep noise sources as far as possible

from quiet area2. Internal acoustics of rooms3. Structural precautions to reduce noise penetrations

Wanted Sound (speech, music) – heard properly; considered desirable

Unwanted Sound (noise) – annoyance; not desired or objectionable

Characteristics of Sound Audible Inaudible

Generation - sound is generated when an object vibrates, causing the adjacent air to move, resulting in a series of pressure waves radiating out from the moving object

Wave – a disturbance or oscillation that transfers energy progressively from point to point in a medium or space without advance by the points themselves, as in the transmission of sound or light

Sound Wave – a longitudinal pressure wave in air or an elastic medium esp. one producing an audible sensation

Frequency the no. of times the cycle of compression and rarefaction of

air occurs in a given unit of time (e.g. 1000 cycles in the period of 1 second = 1000 cps = 1000 Hertz)

the no. of cycles per unit time of a wave or oscillation the no. of complete cycles per second (frequency of

vibration) the rate of oscillation of molecules by sound (frequency of

vibration) measured in cycles per second (Hertz) Pitch – frequency of sound vibration; the predominant

frequency of a sound as perceived by the human ear Vibration – the back and forth motion of a complete cycle Cycle – full circuit by a displaced particle Period – the time required for one complete cycle

Frequency 20 – 20,000 Hz – approx. audio frequency range of human

hearing; 600 – 40,000 Hz – critical frequency for speech

communication Tone – composed of a fundamental frequency with multiples

of the fundamental, called Harmonics Pure Tone – sound composed only of 1 frequency Musical sounds are combination of many pure tones Frequency bands – used to express division of sounds into

sections (Octave bands are the most common) 9 Octave Bands – 31.5, 63, 125, 250, 500, 1000, 2000,

4000, 8000 Hz

Velocityvaries according to the medium of transmission; approx. 1100 fps in air at normal temperature and pressure

Wavelength Distance between similar points on successive waves; the distance

the sound travels in one cycle Relationship between wavelength, frequency, and velocity: Λ = c/f

Λ = wavelength, ft.2c = velocity of sound, fpsf = frequency of sound, Hz (cps)

Low frequency sounds: characterized by long wavelengths High frequency sounds: characterized by short wavelengths Sounds with wavelengths ranging from ½” – 50’ can be heard by

humans, 1000, 2000, 4000, 8000 Hz

Magnitude Sound power (watts) – amount of energy produced by a

source Intensity – describes the energy level; unit is watts/cm2 Loudness (what is perceived) – related to the Intensity Level

(IL) or Sound Pressure Level (SPL) The Sound Pressure Level (SPL) is equivalent to the Sound

Intensity Level (IL) Intensity Level is expressed in decibels Decibel – dimensionless unit used to express the ratio of

two numerical values of a logarithmic scale

Sound Absorption - some absorb low frequency energy; some absorb high frequency energy

Noise Reduction by AbsorptionNoise levels in a room are highest for a given source if the room’s surfaces are primarily sound reflecting; lowest if there are large areas of sound absorbing materials (e.g. sound absorbing ceilings

Reflections – sound foci/diffused

Reverberation – prolongation of sound; persistence