Biophysics of Human voice

The Breathing is one of the most important physiological process of our body in which, we normally inhale (breathe in) and exhale (breathe out) air. While exhaling, our vocal cords vibrate with a little force. This is a physiological process by which the sound / voice is generated.

To understand this completely, it is first important to know its Biophysics.

Let us discuss the systems and the physical techniques that are responsible for sound generation.

The following parts of our body play significant role in sound production:

Vocal Cords/Vocal Box: Vocals cords are a part of the larynx (an organ found in the neck). These are muscle tissue flaps or folds within the larynx that vibrate to produce sound. These cords may be of different thickness and lengths, depending mainly upon the gender.

Larynx: The larynx is also called the sound/vocal box, and is situated in the neck region. It may be noticed that we normally speak only when we exhale the air during our breathing process. At this time, 2 activities occur simultaneously – exhaling of air from lungs and contraction of the larynx muscles closer. This causes vibrations of the vocal cords, thereby producing sound. Apart from sound production, larynx also protects the entry of any food particle into the windpipe and allows a clear passage to air to flow from and to the lungs.

Pharynx: The pharynx is a part of the throat. It is composed of sphincter tissues and lies above the oesophagus and behind the larynx (posteriorly). The sphincter tissues of the pharynx allow only one side entry, and play an important role in preventing the food from coming back up.

Glottis: This is the part of the larynx consisting of the vocal cords (vocal folds or flaps), also known as vocal apparatus of the larynx. 

Epiglottis: This is the part of glottis, consisting of leaf shaped cartilaginous flaps or folds. These folds are mainly responsible for producing sound (voice) by creating vibrations in different variations in terms of frequency, wavelength, time-period, amplitude, pitch, etc. The epiglottis plays 2 roles – in sound production and in the breathing process where it prevents the entry of any food particle into trachea. The epiglottis is less thick in males as compared to females, therefore, it vibrates less and the sound produced is of lower frequency and pitch in males.

Laryngeal Pharynx: This is the area between epiglottis and oesophagus. It guides and monitors the way of food towards the oesophagus and that of air towards lungs.

Trachea & Trachea Rings: The trachea is a sort of hollow tube, also known as the windpipe. It is composed of trachea rings (to hold the tube in a widened position), situated in the upper most part of the respiratory system to provide clear passage for air flow during breathing.

Sound: The sound is always produced in longitudinal wave form, consisting of compressions and rarefactions through a medium like air. 

There are following 5 elements which contribute in sound production:

1. Amplitude (in dB) – Maximum vertical height of a wave

2. Frequency / Pitch (in Hz) – Maximum number of waves per second

3. Time-period (in seconds) – Total time taken to complete one wave

4. Velocity (in cm/sec) – Total distance travelled by a sound wave

5. Wave length (in cm) – Maximum horizontal length of a wave

Audible ranges:

We are able to hear sound, ranging from 20 to 20,000 Hz in terms of frequency. Men and women can hear sounds from 60 to 180 Hz and from 160 to 300 Hz respectively.

Human ear can hear sounds from 0 dB (threshold) to 120-130 dB in terms of amplitude (loudness).

The sound range is also categorized as:

Whispering sound: 0 to 40 dB

Normal sound: 40 to 70 dB

Loud or noisy sound: 70 to 100 dB

Plane take-off sound: 100 to 140 dB

Biophysical Properties:

  • The cartilaginous flaps or folds of epiglottis are thicker and shorter in men than in women.
  • The frequency (pitch) of sound is less and amplitude is higher in men than in women.
  • Men have louder voices due to higher amplitude.
  • The aggressive/loud/soft voices can easily be produced by regulating pressure on sound waves for talking/singing.

Rarest voice is Contralto: It is the lowest female voice starting from middle C scale upto highest level of F scale and even above.

The maximum vocal range recorded by Guinness World Record is upto 10 octaves in Piano.

Thank you.

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