N. V. Tatsenko introduction to theoretical phonetics of english

Fricatives are consonants that are produced by impeding, but not completely blocking the airflow, i. e., there is a narrow gap between the active and the passive articulator along which the airflow can leave the oral cavity. There are nine fricatives in English: labio-dental [f] and [v], dental [9] and [6], alveolar [s] and [z], post-alveolar [f] and [3], and glottal [h].
T



Figure 4.5 - Dental Fricatives [0] and [d]
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Figure 4.4 - Labio-Dental Fricatives [f] and [v]


he lower lip is very close to the edge of the upper front teeth, thus forming an incomplete obstruction. When the air goes through the narrowing it causes slight friction (hence the term fricative). For [f] the vocal cords do not vibrate; there may be some vibration accompanying [v] when it occurs in word initial position as in vast or between vowels as in never. The fricative noise is never very strong and is scarcely audible in the case of [v]. Example words: 'fan', 'van'; 'safer', 'saver'; 'half, 'halve'.
The tip of the tongue is either close to the edge of the upper teeth or slightly projected between the teeth. For [9] the friction is as strong as for [f], for [6] it is gentler. For [9] the vocal cords do not vibrate; they vibrate for [6] when it occurs in word initial position, before a vowel or in intervocalic positions (that, rather). Example words: 'thumb', 'thus'; 'ether', 'father'; 'breath', 'breathe'.
The dental fricatives are sometimes described as if the tongue were placed between the front teeth, and it is common for teachers to make their students do this when they are trying to teach them to make this sound. In fact, however, the tongue is normally placed behind the teeth, with the tip touching the inner side of the lower teeth. The air escapes through the gaps between the tongue and the teeth. As with [f], [v], the fricative noise is weak.
Other fricatives are produced with different places of articulation: for the alveolar fricatives [s] and [z], the tip of the tongue is close to the alveolar ridge with the same place of articulation as [t], [d]. The teeth are very close together. The friction for [s] is strong, even stronger than for [9]. For [s] the vocal cords do not vibrate; they vibrate for [z] when it occurs before vowels or in intervocalic positions (zone, easy). Example words: 'sip', 'zip'; 'facing', 'phasing'; 'rice', 'rise'.