Voiced dental fricative

The symbol in the International Phonetic Alphabet for this sound is eth ⟨⟩, which was taken from the Old English and Icelandic alphabets. In Old English, the letter was used interchangeably with thorn ⟨⟩ for either this sound or its unvoiced counterpart; in Icelandic, eth is solely used for this sound, and thorn its unvoiced counterpart. Such fricatives are often called "interdental" because they are often produced with the tongue between the upper and lower teeth (as in Received Pronunciation), and not just against the back of the upper teeth, as they are with other dental consonants.

The letter ⟨⟩ is sometimes used to represent a voiced dental approximant, a similar sound, which no language is known to contrast with a dental non-sibilant fricative. However, the approximant can be explicitly indicated with the lowering diacritic: ⟨⟩. Rarely, this sound has also been transcribed as a dentalised alveolar approximant ⟨⟩. It has been proposed that either a turned ⟨⟩ or reversed ⟨⟩, among others, be used as a dedicated symbol for the dental approximant; however, despite occasional usage, none have gained general acceptance. Like the fricative, the approximant may also be articulated interdentally in some languages.

Dental fricatives are rare as phonemes. Almost all languages of Europe and Asia lack the sound. Native speakers of languages without the sound often have difficulty enunciating or distinguishing it, and they replace it with a voiced alveolar sibilant , a voiced dental stop or voiced alveolar stop , or a voiced labiodental fricative ; known respectively as th-alveolarization, th-stopping, and th-fronting. As for Europe, there seems to be a great arc where the sound (and/or its unvoiced variant) is present. Most of Mainland Europe lacks the sound. However, some "periphery" languages such as Greek have the sound in their consonant inventories, as phonemes or allophones.

Within Turkic languages, Bashkir and Turkmen have both voiced and voiceless dental non-sibilant fricatives among their consonants. Among Semitic languages, they are used in Modern Standard Arabic, albeit not by all speakers of modern Arabic dialects, and in some dialects of Hebrew and Assyrian.

Features

Features of a voiced dental non-sibilant fricative:

• Its manner of articulation is fricative, which means it is produced by constricting air flow through a narrow channel at the place of articulation, causing turbulence. It does not have the grooved tongue and directed airflow, or the high frequencies, of a sibilant.
• Its place of articulation is dental, which means it is articulated with either the tip or the blade of the tongue at the upper teeth, termed respectively apical and laminal. Note that most stops and liquids described as dental are actually denti-alveolar.
• Its phonation is voiced, which means the vocal cords vibrate during the articulation.
• It is an oral consonant, which means that air is not allowed to escape through the nose.
• It is a median consonant, which means it is produced by directing the airstream down the midline of the tongue, rather than to the sides.
• Its airstream mechanism is pulmonic, which means it is articulated by pushing air only with the intercostal muscles and abdominal muscles, as in most speech sounds.