2. 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)
3. 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.
Submitted By: Makwana Hardik (I.T- 40)
4. 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.
Submitted By: Makwana Hardik (I.T- 40)
5. 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.
Submitted By: Makwana Hardik (I.T- 40)
6. Remidies for good acoustics:
A hall or an auditorium is said to be acoustically good if they satisfy the following
Submitted By: Makwana Hardik (I.T- 40)
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.
8. 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
Submitted By: Makwana Hardik (I.T- 40)
