sound

Frequency

  • The number of vibrations made by a vibrating body in one second is known as its frequency.
  • The SI unit of frequency is hertz (Hz).

Amplitude

  • The maximum displacement of a vibrating body from its mean position is known as its amplitude.
  • The SI unit of amplitude is metre (m).
  • The letter 'a' represents the amplitude of sound waves

Sound wave

  • A sound wave consists of altering compressions ( high pressure region) and rarefactions (low pressure region)
  • The frequency and amplitude are the two important properties of a sound wave.

Characteristics of sound

loudness

timbre

pitch

Pitch is a characteristic of a sound that depends upon its frequency.

It refers to how shrill or flat a sound is

higher the frequency, higher will be the pitch ( shrill sound), while lower the frequency lower would be the pitch ( flat or hoarse sound).

Pitch of a sound can be changed by changing the length, thickness or tautness of the vibrating string.

  • By shortening or tightening the string, the pitch gets higher.

Examples

  • The number of vibrations increase when we use a thinner string , thus raising the pitch.
  • In tabla, a tight drum skin gives a high pitched sound than a loose drum skin.
  • The voice of women is generally pitched compared to the voice of men. This is because women have shorter vocal cords which vibrate with high frequency to produce a high pitched sound.
  • A guitar produces musical sounds through vibration of strings. To change the pitch, guitarists change the length of the string by pressing the string down at different places along the neck of the guitar.
  • A standard piano keyboard has 88 keys. When you press a key on the piano, it causes a small hammer inside the piano to hit a string. The string vibrates and u hear the sound.

Low pitch left; high pitched right side

Loudness is the characteristic of a sound that depends on the amplitude of the sound wave.

A body vibrating with larger amplitude will produce a louder sound and the one vibrating with smaller amplitude will produce a softer sound.

Loudness also depends on the distance between the listener and the source. Larger the distance between the source and the listener, lesser is the loudness of sound heard by the listener.

Loudness of a sound is measured in decibel (dB).

A decibel is one tenth of a 1 bel (B).

The loudness unit called the Bel was named after Alexander Graham Bell, the inventor of the telephone.

the table

Quality or timbre is the characteristic that allows us to distinguish between the sounds having same pitch and loudness.

The sound quality of each instrument is different

music and loudness

music is a pleasant sound that is produced due to regular and periodic vibrations.

Noise is a sound which is not pleasing to our ears.

it is produces due to irregular and non periodic vibrations.

Audible and Inaudible sounds

Sounds below 20 Hz and above 20,000 Hz cannot be detected by the human ear. These sounds that cannot be heard by us are called inaudible sounds

human beings can hear sounds of frequencies between 20 Hz to 20,000 Hz.

sounds with frequency ranging from 20 Hz to 20,000 Hz are known as audible sounds

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