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Speech Production. Physics of the Human Body. The Physics of Speech. Speech sounds are produced by changes in pressure of an outward flow of air from the lungs. The final sound is dictated by the way the air moves through the nose, mouth, and throat (collectively: the vocal apparatus).

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speech production

Speech Production

Physics of the Human Body

the physics of speech
The Physics of Speech
  • Speech sounds are produced by changes in pressure of an outward flow of air from the lungs.
  • The final sound is dictated by the way the air moves through the nose, mouth, and throat (collectively: the vocal apparatus).
lungs trachea
Lungs / Trachea
  • Nerve Impulses from the brain signal the diaphragm to raise, pushing air from the lungs, and allowing them to deflate.
  • Air then travels from the lungs to the trachea (sometimes called the “windpipe”) and into the larynx.
the respiratory system and speech
The Respiratory System and Speech:
  • The respiratory system and speech are interconnected:
    • The average fundamental frequency and intensity increase with higher lung volume initiation levels in untrained voices. (1)
    • The Lombard Effect: The voice naturally raises in intensity level when given the condition of noise. When wearing headphones at a loud level (70 dB), the listener’s voice will raise unless the listener consciously controls his volume level. (2)
the larynx voicebox outside8
The Larynx (Voicebox) [Outside]
  • The outside structure of the larynx primarily serves as protection for the inside structure and the trachea.
  • The larynx also closes at the epiglottis and glottis during swallowing to protect the lungs from receiving unwanted artifacts (such as food or water).
the vocal folds vocal cords
The Vocal Folds (Vocal Cords)
  • The vocal folds are chiefly responsible for modulating the airflow from the lungs and determining its resonant frequency.
  • The folds vibrate when they are closed to obstruct the airflow through the glottis. The folds are forced open by increased air pressure in the lungs, and closed again as the air rushes past the folds.
Resonance is the tendency for a system to amplify itself when excited by certain frequencies.

It is important to note that resonant frequencies are determined by the physical dimensions of the vibrating object.

resonance example
Resonance Example

When pushing a child on a swing, the preferred path as per the specifications of the system is straight up and down, and can be accomplished with ease (this path is the “resonant frequency” which results in greater amplification [height in this instance]). However, when pushing the child in a different direction, it becomes more difficult to produce such a result.

Resonant Frequencies are determined by physical dimensions of the vocal cords.
  • Imagining the vocal folds as a “closed tube” helps demonstrate the process of determining a fundamental frequency.
  • The longer the “tube,” the lower the frequency.
  • In males, one of the nine cartilages of the larynx (the 'Adam's apple') increases in size during puberty. This elongates the ligaments of the vocal folds which then vibrate at a lower frequency making men's voices generally deeper than women's.
false vocal cords
False Vocal Cords
  • The “false vocal cords” have are thick membranes that are used in protecting the more delicate “true vocal cords.”
    • While they have nominal use in normal speech, they are used quite a bit while screaming, or high-intensity speech production. This can often lead to muscle tension dysphonia, an unequalness in tension while speaking, this is generally caused by excessive straining in voice production. (3)
issues arising within the larynx
Issues Arising within the Larynx
  • Potential symptoms of larynx disorders are hoarseness, loss of voice, pain in the throat or ears, and breathing difficulties.
      • Paresis: weakness of one or both vocal folds, causing inefficient opening and closing.
      • Polyps and Nodules caused by overuse and cigarette smoke will change the quality of the voice, leading to hoarseness and pain.
      • Ulcers can lead to throat pain and a tired voice.
the vocal tract
The Vocal Tract
  • The shape of the vocal tract transforms raw sound from the vocal folds into recognizable sounds.

The final output of sound follows a model of:

A  B*  C.

Where A is the airflow of varying pressure after leaving the vocal folds (sound is a pressure wave.)

And B is the variable dictating the final construct of the sound.


The vocal tract acts like a variable filter because it reacts differently at different frequencies. (1)

It is variable because by changing the position of your tongue, jaw, lips, etc. you can change the overall frequency response.

the variable filter voice articulators
The Variable Filter (Voice Articulators)
  • The articulators that make intelligible sound out of the raw sound wave produced in the larynx are:
    • The Pharynx
    • The Velum (Soft Palate)
    • The Oral Cavity
    • The Nasal Cavity
  • All of these articulators have the ability to change the nature of the original sound wave. This is one of the principal reasons the human voice is so complex compared to other sounds!
the pharynx
The Pharynx
  • While serving a primarily protective function in not allowing food to reach the lungs, the Pharynx length can be changed to raise or lower the fundamental frequency slightly by raising or lowering the larynx and soft palate simultaneously. (3)
the soft palate velum
The Soft Palate (Velum)
  • The soft palate separates the oral cavity (mouth) from the nasal cavity in order to produce oral speech sounds. If this separation is incomplete, air escapes through the nose during speech and the speech is hypernasal.
the oral cavity
The Oral Cavity

The Oral Cavity primarily consists of the:

  • Tongue
  • The Hard Palate
  • Lips

The oral cavity is the most important component of the vocal tract because its size and shape can be varied by adjusting the relative positions of the palate, the tongue, the lips, and the teeth.

hard palate
Hard Palate
  • The interaction between the tongue and the hard palate is essential in the formation of certain speech sounds, notably /t/, /d/, /c/ and //.
voiced and unvoiced sounds
Voiced and Unvoiced Sounds
  • Voiced sounds are followed by /z/, /d/ sounds, such as 'plays', 'played', while unvoiced sounds are followed by /s/, /t/ sounds, such as 'likes', 'liked'.
  • Touch your throat when you say the sound- when it is voiced, you should be able to feel a vibration.
the nasal cavity
The Nasal Cavity
  • Most voiced sounds are in the pharyngeal and oral cavities, the nasal sounds /m/, /n/, and /ng/ require added resonance in the nasal cavity.
what is pitch
What is Pitch?
  • Pitch is the perceived fundamental frequency of a sound. It may not be entirely accurate due to overtones, partials, or harmonics.
  • A person’s natural pitch is determined by the resonant frequency of the vocal folds. The smaller the frequency (measured in Hz), the lower the perceived sound.

Average Pitch:

Adult Male – 125 Hz

Adult Female – 220 Hz

Children – 300 Hz

artificial changes to pitch
Artificial Changes to Pitch
  • Pitch can be influenced artificially by the introduction of foreign elements such as:
      • Helium
      • Electronic Manipulation (Pitch-Shifting / AutoTune)
      • Speed of Playback (Alvin + Chipmunks)
  • An excessively awesome, yet equally dangerous manipulation of sound occurs when the human voice travels through helium. Since the speed of sound is greater through helium, the resonances occur at higher frequencies than in air.

Ordinary Speech:

Helium Speech:

Pitch in Air:

Pitch in Helium: