10.2 - Sound Produced by Humans

Sound is produced when objects vibrate, and these vibrations cause air particles to move, creating pressure waves. Humans produce sound through vocal cords located in the larynx (voice box). The process of sound production in humans involves the following steps:

1. **Air from Lungs**: The process begins when air is pushed out from the lungs. The lungs act as the air reservoir that provides the necessary airflow to produce sound.

2. **Vocal Cords Vibration**: The air passes through the trachea (windpipe) into the larynx, where the vocal cords are located. The vocal cords are two bands of muscle-controlled tissue. When air passes through the vocal cords, they vibrate. The tension of the vocal cords can be adjusted to vary the pitch of the sound produced. When the vocal cords are tight, the sound produced is higher in pitch, and when they are loose, the sound produced is lower in pitch.

3. **Resonance in the Mouth and Throat**: The vibrations from the vocal cords are amplified and modified in the throat, mouth, and nasal cavity. These are known as resonators. The shape and size of the oral cavity (mouth) and nasal cavity influence the quality and tone of the sound. This is why each person's voice is unique.

4. **Articulation**: The sound produced by the vocal cords is shaped into speech or other sounds through the movement of the tongue, teeth, and lips. These are called articulators. By changing the position of the tongue and lips, humans are able to produce different sounds, such as vowels and consonants.

Key Components Involved in Sound Production:

• Lungs - Provide the air supply.
• Vocal Cords - Vibrate to produce sound.
• Throat and Mouth - Amplify and modify the sound.
• Articulators - Shape the sound into speech.

Pitch and Loudness of Human Sound:

The pitch of the sound produced by the human voice depends on the frequency of the vibrations of the vocal cords. Higher frequencies produce higher-pitched sounds, and lower frequencies produce lower-pitched sounds. The loudness of the sound depends on the amplitude of the vibrations. Larger vibrations cause louder sounds, while smaller vibrations produce quieter sounds.

Pitch Formula: The frequency ($f$) of the vibration is related to the pitch of the sound. The formula for frequency is:

$f = \frac{1}{T}$

Where:

• $f$ is the frequency (in hertz, Hz),
• $T$ is the time period of one vibration (in seconds, s).

Loudness of Sound: The loudness of a sound produced by humans is measured in decibels (dB). The louder the sound, the higher the amplitude of the vibrations of the vocal cords. The loudness can be described by the following relationship:

$L = 20 \log \left( \frac{A}{A_0} \right)$

Where:

• $L$ is the loudness of the sound in decibels (dB),
• $A$ is the amplitude of the sound wave,
• $A_0$ is the reference amplitude (usually the smallest audible sound).

The range of human hearing is generally from 20 Hz to 20,000 Hz. However, the frequency range of the human voice typically lies between 85 Hz to 1,100 Hz for most people, with women typically having higher pitch ranges than men.

Humans are capable of producing a wide variety of sounds, from normal speech to singing, shouting, and whispering, by controlling the tension in the vocal cords, the amount of air pressure from the lungs, and the resonance in the vocal tract.