PRAXIS Aerodynamics in Speech

air. Understanding air pressure, flow, and volume is crucial in comprehending both normal and disordered speech.

irregularities or deficiencies in the supply and valving of air. Clinical assessment techniques often utilize measures of air pressure, flow, or volume.

one direction only, moving from a region of greater pressure to one of lesser pressure. When the vocal tract is closed at some point, there is the potential for the buildup of air pressure behind the closure.

English speech sounds are egressive, which means that during sound production, air flows from the inside (usually the lungs) to the outside (the air around us).

the lungs. Air is inspired by enlarging the lung cavity, and then the muscles activate to return the lung cavity to a smaller size.

an increase in air pressure within the lungs. This overpressure in the lungs, relative to the atmosphere, is the source of the egressive air flow for all speech sounds.

ordinary breathing. The volume of air inspired and expired during speaking is not much different from that during quiet respiration.

the laryngeal, oral, and nasal sections.

larynx. When the vocal folds close tightly, no air can escape from the lungs. If the folds are maximally open, air passes through the larynx easily. If the folds are closed with moderate tension, the buildup of air pressure beneath them eventually blows them apart, releasing a pulse of air.

The alternation of closed and open states of the vocal folds, occurring many times per second, is called voicing. This process generates successive pulses of air from the vocal folds, serving as a source of acoustic energy for all voiced sounds, such as vowels.

The vocal folds are partly closed to represent the vibratory pattern of opening and closing, and the nasal tube is tightly closed because English vowels are typically nonnasal unless they are before or after nasal consonants. The open oral tube represents the open oral cavity in vowel articulation, allowing the acoustic energy from the vibrating vocal folds to pass through.

The laryngeal constriction is completely open, allowing air from the lungs to pass readily through the larynx and into the oral cavity. The constriction at the velopharynx is closed, indicating no air flow through the nasal tube. The oral constriction is also closed during the period of stop closure. After this period, the oral constriction opens rapidly, allowing a burst of air to escape from the oral pressure chamber.

Assuming an appropriate duration of stop closure, the air pressure developed within the oral cavity during voiceless stops can be nearly equal to that in the lungs because the open vocal folds permit an equalization of air pressure in the airway from the lungs up to the oral cavity. As a result, voiceless stops have high intraoral air pressures. It is worth noting that children may use greater intraoral air pressures than adults.

is similar to that for voiceless stops but with a very narrow constriction instead of a complete oral constriction. This narrow constriction is required for producing fricative noise. With the velopharyngeal constriction tightly closed and the laryngeal constriction open, voiceless fricatives like /s/ and /f/ have high intraoral air pressures. Voiceless stops and fricatives are sometimes referred to as pressure consonants.

Voiced stops and fricatives differ from voiceless stops and fricatives in having vibrating vocal folds. Therefore, the models for voiced stops and fricatives (Figure 2.27b and c) would have a partial laryngeal constriction to represent voicing of these sounds. Because some air pressure is lost in keeping the vocal folds vibrating (i.e., pressure across the glottis drops), the voiced stops and fricatives have smaller intraoral air pressures compared to their voiceless counterparts.

a partial constriction at the larynx to represent the vibrating vocal folds, and a complete oral constriction to represent the stop-like closure in the oral section of the vocal tract. In nasal consonants, the acoustic energy of voicing is directed through the nasal cavity, and very little air pressure builds up within the oral chamber.

The oral constriction for these sounds is only slightly greater than that for vowels, resulting in very little intraoral air pressure buildup.

Pressures and flows are used to describe the function of various parts of the speech system. They can help differentiate between normal efficient operation and inefficient pathological states. Excessive air flow in the larynx may indicate inefficient functioning and can lead to breathiness or hoarseness.

recording air flow from the nose during segments that are normally nonnasal. It is often signaled by inappropriate nasal air flow during stops or fricatives and reduced levels of intraoral air pressure. Multiple measurements of pressures and flows may be needed to identify the specific problem.

Reduced levels of intraoral air pressure for consonants can be related to different factors, including respiratory weakness (insufficient air pressure), velopharyngeal dysfunction (loss of air through the nose), or an inadequacy of the oral constriction (allowing excessive air to escape).

Aerodynamic assessment is crucial in clinical settings, especially when dealing with structural defects like cleft palate or physical control problems seen in conditions such as cerebral palsy, vocal fold paralysis, and other neurological disorders.

Young children may use higher intraoral air pressure than adults when producing consonant sounds. Therefore, normative pressure data from adults should be used cautiously when evaluating children's speech.

Due to the higher pressures in children's speech, they must close the velopharyngeal port even more tightly than adults during the production of stop or fricative consonants to prevent nasal air loss.

frequency, amplitude, and duration.

Frequency refers to the rate of vibration of a sound. A faster rate of vibration corresponds to a higher pitch, while a slower rate results in a lower pitch. Frequency is directly related to the perception of pitch in speech.

Amplitude pertains to the strength or magnitude of vibration of a sound. A higher magnitude of vibration results in a louder sound, while a lower magnitude produces a softer sound. Amplitude is directly associated with the perception of loudness in speech.

The actual amplitude of vibration in speech is very small and challenging to measure accurately. Therefore, sound intensity or sound pressure level is commonly used for actual speech measurements to assess the amplitude.

Duration refers to the total time over which a vibration continues. It is directly related to the perception of the length of a speech sound. Longer vibrations correspond to longer perceived durations in speech.