SUBJECT :- PHYSICS

TOPIC :- ACCOUSTIC

BRANCH :- CIVIL (151080106005)

PREPARED BY. :- KANSARA MEGHAN

INTRODUCTION: Acoustics:Physics dealing with generation, propagation andapplications of sound Architecture of Acoustics:Physics dealing with construction of buildings with :intention to provide good audible sound .History:Prof. Wallace C. Sabine from HarvardUniversity performed thesystematic study about acoustical defectsand presented Sabine's theory ofreverberation to minimize acousticaldefects and proposed precautionsregarding the same.

SOUNDWAVES:

o Any vibrating body will displace the air layers nearby and initiate mechanical wave which propagates in the medium through alternate compression and rarefactions, sets the ear drum vibrating and causes the sensation of hearing.

• PROPERTIES:

• Mechanical wave which propagates in the medium via• alternate compression and rarefactions• Propagation of sound needs an elastic medium• Sound waves are longitudinal in nature• Creates Pressure variation region during propagation• Can be classified on the basis of frequency as Infrasonic• waves (less than 16 Hz), Audio waves (16 to 20 KHz) and• Ultrasonic waves (greater than 20 KHz)• Velocity of sound wave depend upon nature and temperature• of the propagating medium

Noise: creates Unpleasant Sensation

Musical Noise: Pleasant Sensation

Pitch: Subjective sensation related with frequency of sound

Timber: Subjective sensation related with quality of sound

Intensity of Sound: Energy transported by sound wave per unit area per unit time

Intensity Level: Logarithmic ratio of intensity produced by the source to the reference intensity

Threshold of Audibility: When I = I0, it’s intensity level becomes 0 dB. This is called threshold of audibility.

Echo: An echo is defect produced due to reflection of sound. When sound is reflected from reflecting surface which is either 17 or meter away or there is 100 ms gap between original sound and reflected sound we can distinct between them. Such a reflection of sound is known as echo.

Reverberation: A sound produced in a volume is reflected multiple times from the various surfaces. As a result sound persists in the volume for sometime of gradually decreasing intensity even the source stop emitting the sound. This persistence of the sound in a room due to multiple reflections, even when the source stops, is known as reverberation.

Reverberation time: It is defined as the time during which the sound energy falls from its steady state value to 10-6 times after the source is cut off.

Coefficient of absorption: It is a ratio of sound energy absorbed by its surface to that of total sound energy incident on the surface.

Sabine or Open Window Unit (OWU): 1 m2 Sabine is the amount of sound absorbed by one square meter area of fully open window.

EYRING’S EQUATION: Sabine’s formula works for large enclosures.

However, it leads to paradox for highly absorptivesurfaces. For instance when a = 1, all sound energyincident on the surface is absorbed and T = 0. Suchroom is called dead room in acoustical terms.

Sabine’s formula does not leads to T = 0 when a =1. Actually, experiments shows that Sabine’sformula is valid only for a 7 0.2.

Eyring proposed modification in the equation asFollowing.

• DEFECT

• Excessive reverberation

• Echoes

• Sound foci

• Dead spots

• Insufficient Loudness

• Noise

• Effect

• Bad quality of sound

• Superposition of sound

• Non-uniform distribution of sound

• Sound of large intensity is focused at focal point

ACOUSTICAL DEFECTS AND EFFECTS: