Voiceless alveolar fricative

Voiceless alveolar fricatives are a type of fricative consonant pronounced with the tip or blade of the tongue against the alveolar ridge (gum line) just behind the teeth. This refers to a class of sounds, not a single sound. There are at least six types with significant perceptual differences:

• A voiceless alveolar sibilant [s] (the standard symbol in the International Phonetic Alphabet or IPA) has a strong hissing sound, as the s in English sink. It is one of the most common sounds in the world.
• A voiceless denti-alveolar sibilant [s̟] or [s̄] (an ad hoc notation), also called apico-dental, has a weaker lisping sound like English th in thin. It occurs in Spanish dialects in southern Spain (eastern Andalusia).
• A voiceless alveolar retracted sibilant [s̠], and the subform apico-alveolar [s̺], has a weak hushing sound (also called "grave" frication) reminiscent of retroflex fricatives. It is used in the languages of northern Iberia, like Asturleonese, Basque, Peninsular Spanish (excluding parts of Andalusia), Catalan, Galician, and Northern European Portuguese. A similar retracted sibilant form is also used in Dutch, Icelandic, some southern dialects of Swedish, Finnish, and Greek. The retracted "S" is also used in Amerindian languages such as Muscogee, Garifuna, and many varieties of Quechua. It was supposedly the standard sound of s in Classical Latin. Its sound is between [s] and [ʃ].
• A voiceless alveolar non-sibilant fricative [θ̠] or [θ͇] (using the alveolar diacritic from the Extended IPA) is similar to the th in English thin. It occurs in Icelandic as well as an intervocalic and word-final allophone of English /t/ in dialects such as Hiberno-English and Scouse.
• A voiceless alveolar lateral fricative [ɬ] sounds like a voiceless, strongly articulated version of English l (somewhat like what the English cluster **hl would sound like) and is written as ll in Welsh.

The first three types are sibilants, meaning that they are made by directing a stream of air with the tongue towards the teeth and have a piercing, perceptually prominent sound.