Acoustics Presentation

AcousticsA science of sounds

Physics

Submitted by: Makwana Hardik N

Classification of Sounds:

• The sounds are classified into three category:

1). Infra Sound (f<20Hz)

2). Audible Sound (20Hz<f<20kHz)

3). Ultra Sound (>20kHz)

Submitted By: Makwana Hardik (I.T- 40)

Musical Sound and Noise

• The sound which produce pleasing effect on ear is called musical sound.

• The musical sound waveform are regular in shape, having definite periodicity and they do not undergo a sudden change in amplitude.

• The sound which produces and jarring effect on ear and is unpleasing to hear is called noise.

• The musical sound waveform are not regular in shape, they do not have definite periodicity and they undergo a sudden change in amplitude.


Terms

• Loudness: – Loudness is a degree of sensetion produced on ear. Thus, loudness varies

from one listener to another. Loudness depends upon intensity and also upon the sensitiveness of the ear.

• Pitch:– It is the sensetion depends upon frequency. Pitch helps in distingush

between a note of high frequency and low frequency sound of same intensity produced by the same musical instrument. A shrill sound is produced by a sound of high frequency.

• Timbre:– It is the quatity of sound which enables us to distingush between two

sounds having the same loudness and pitch. It depends on the presence of overtones.


Terms

• Echo: – An echo is heard due to reflection of sound from a distant sound-reflecting

object. If the time interval between the direct sound and reflected sound is less than 1/15th of a second.

• Reverberation:– The persistence or prolongation of sound in a hall even through the source

is cut off is called reverberation.

• Absorption Coefficient:– The sound absorption coefficient ‘a’ of a material is defined as the ratio of

sound energy absorption by it to the total sound energy incident on it.

– It is defined as the reciprocal of the area of the sound absorbing material which absorbs the same amount of sound energy as that of 1m2 of an open window.


Remidies for good acoustics:


A hall or an auditorium is said to be acoustically good if they satisfy the following condition.

1). The quality of the sound should be uniform throughout the entire hall or auditorium.

2). There should not be any overlapping of sounds.

3). The loudness of the sound should be uniform throughout the hall or auditorium. To achieve this a public address system can be used in big halls.

4). The presences or absence of audience should not affect the quality of sound.

5). Resonance effect should have a proper reverberation time.

6). The hall should have a proper reverberation time .

7). The external noises should not disturb the proceedings inside the hall or auditorium.

8). There should not be any echelon effect.

List of values of absorption coefficient:


Material 125Hz 250Hz 500Hz 1 KHz 2 KHz

carpet 0.01 0.02 0.06 0.15 0.25

concrete 0.01 0.02 0.04 0.06 0.08

Marble 0.01 0.01 0.01 0.01 0.02

Vinyl tile 0.02 0.03 0.03 0.03 0.03

Wood parquet

0.04 0.04 0.07 0.06 0.06

Wood flooring

0.15 0.11 0.1 0.07 0.06

Glass 0.18 0.06 0.04 0.03 0.02

List of values of loudness in dB of in various infrastructue and Surrounding:


Weakest sound heard 0dB

Whisper Quiet Library at 6' 30dB

Normal conversation at 3' 60-65dB

Telephone dial tone 80dB

City Traffic (inside car) 85dB

Train whistle at, Truck Traffic 90dB

Jackhammer 95dB

Subway train at 200' 95dB

Level of hearing loss 90-95dB

Hand Drill 98dB

Power mower 107dB

Motorcycle 100dB

Sandblasting 115dB

Pain in ears 125dB

Acoustics Presentation

Science

Transcript of Acoustics Presentation