As we have seen before, vowels are essentially characterised by the absence of closure of the vocal tract, so that the air can pass through it in a relatively unimpeded way. The opposite is true for consonants. Here, the characteristic feature is that there is almost always some form of obstruction or obstacle – or at least a narrowing of the vocal tract – which causes perturbations in the air flow.
There are essentially three major ways of classifying consonants, according to their place of articulation, manner of articulation and according to their voicing. We’ll discuss each of them separately in the following sections.
As we have already seen for vowels, when there are fairly regular pulses from the glottis filtering the airstream, we have incidences of voicing. Voicing is not only possible for vowels, but may also occur with – and hence influence the quality of – consonants. Since this type of filtering action that ‘drives’ the focal folds uses up part of the overall energy available to the consonant, voiced consonants tend to be weaker than voiceless ones. For this reason, the former are also sometimes labelled with the Latin term lenis (soft) and the latter with fortis (strong). Voiced consonants show similar vertical striations to vowels on a spectrogram, although they are often weaker and possibly also shorter, and therefore show up a little less clearly. To understand the difference between voiced and voiceless consonants better, let’s do a little exercise.
For most native speakers of English, there will be a clear difference in the realisations of these first consonants in that /p/ will usually make the piece of paper move as it is accompanied by a slight puff of air, technically known as aspiration, but you should also feel that the force in producing it is much stronger than when making the /b/, whereas you can probably feel the strong constriction made inside the larynx for the voiced sound, which ‘soaks up’ much of the energy.
The term manner of articulation refers to the way in which the obstruction inside the oral cavity is made. According to this, we can establish a few different classes of consonants that each show characteristic features which usually make them identifiable on a spectrogram with a bit of practice.
For plosives – also called stops – a solid obstruction is built up somewhere within the oral tract, initially completely blocking the airstream coming up from the larynx. This blockage is then usually released abruptly, so that the air that was compressed behind the obstacle can escape with a kind of explosive movement, producing a ‘cracking’ or ‘popping’ sound. The group of ‘ordinary’ plosives in English comprises /p/ & /b/, /t/ & /d/, /k/ & /g/, where for each pair, the first is voiceless and the second voiced. Because of their ‘explosive’ nature, the audible phase for plosives is generally quite short, although the closure phase before the burst is quite variable. One important thing to remember when one is transcribing normal everyday running speech is that sometimes plosives at the ends of words don’t actually get released.
For additional information, take a look at the plosives section of my Practical Phonetics course.
Nasal consonants in English are fairly limited in number. There are only three – /m/, /n/ & /ŋ/ – and these correspond to the voiced plosives referred to above, with the added feature that during their production the velum is lowered. This allows the air to escape through the nasal cavity instead of the oral one, in effect changing the filter. It also reduces the energy of the nasal consonant, as well as the characteristic patterns produced by it. The voicing can again be seen in vertical striations in a spectrogram, but this time, they mainly occur in a rather low frequency region. An illustration of this can be found in the nasals section of my Practical Phonetics course.
The English ‘pure’ fricatives are /f/ & /v/, /θ/ – as in thin – & /ð/ – as in then –, /s/& /z/, /ʃ/ – as in fish – & /ʒ/ – as in beige –, and /h/. Where there are pairs, the second one is again voiced. Fricatives are produced, not through a complete closure, such as for plosives, but by creating a partial obstruction of the airstream. This makes turbulence arise at or near the point of obstruction, where the airstream is now forced through a greatly narrowed channel. The effect is similar to strong winds blowing through a tunnel, where we may get a slow whistling sound. This whistling is particularly noticeable in the two pairs /s/& /z/ and /ʃ/ & /ʒ/, which is why they are also referred to as sibilants (and sometimes also stridents). Fricatives generally tend to be fairly long and are therefore usually easier to see on a spectrogram, not least because they also exhibit very characteristic noise frequencies. The last fricative in the series, /h/, represents a special case since it is produced with a relatively small obstruction, and this not inside the oral tract, but rather within the larynx. Rather than exhibiting very specific noise patterns of its own, it therefore represents something like a voiceless version of the vowel following it. You can test this by producing a sustained ‘plain’ [h], which ought to sound rather like [hə:]. Additional information can again be found in the fricatives section of my Practical Phonetics course.
Affricates are essentially a combination of a plosive and a following fricative, where the quality of the plosive remains largely the same, but the fricative part tends to be shorter than in a ‘pure’ fricative. Also, genuine affricates are homorganic, which means that the two sounds are produced in the same region, even if, individually, they would generally be produced in different places with a movement from one to the other. For an illustration, see the affricates section of my Practical Phonetics course. The two pairs of affricates generally assumed to occur in English are /tʃ/ & /dʒ/ and /tɹ/ & /dɹ/, where you can simply think about the final sound in the latter pair as representing an <r>.
Lateral consonants differ from the other consonants in one very distinct feature. Whereas for all other consonants1 the air can usually escape evenly around both sides of the relevant active articulator, for the English lateral /l/ (clear l) and its velarised variant [ɫ] (dark l), the air is allowed to escape over the side of the tongue, rather than its middle.
Another group of sounds that is often listed with the consonants is that of the so-called approximants. Phonetically speaking they are actually like vowels, but for phonological reasons to be discussed later are generally grouped with the consonants, as can also be seen from the consonant chart further below. They don’t exhibit the kind of ‘random’ noise that can be seen in consonants, but usually show formant patterns similar to vowels. For this reason, at least /j/ and /w/, that are phonetically similar to /i/ and /u/ respectively, are often also referred to as semi-vowels. These two usually function as relatively slow on- or off-glides to pure vowels, i.e. as linking elements.
The transitions for the two remaining approximants, /ɹ/ – phonetically like a neutral vowel /ə/, but with the tongue tip curled back and making contact with the roof of the mouth – and /l/ take place slightly more rapidly, but we can still discern clear formant patterns, most notably for /ɹ/ in a lowering of the third formant (F3), which is not present in the lateral .
Illustrations and additional explanations for most of the above can be found in the the approximants section of my Practical Phonetics course.
Place of articulation refers to the location where the constriction or obstruction of the vocal tract occurs, as well as to the active or passive articulator(s) involved in the production of the consonant.
As the name implies, a bi-labial articulation is achieved by using both lips as active articulators. For English, more or less the only bilabially produced (and distinctive) consonants are the plosives /p/, /b/ & /m/.
In a labio-dental articulation, the lower lip and the upper teeth act together in producing the sound. In fairly standard English, only the two fricatives /f/ & /v/ belong to this category. One further sound – that is still considered non-standard, but seems to become more frequent for some younger speakers – is a labio-dental approximant [ʋ]. It represents a realisation of /ɹ/ which some people regard as one of the features of a new emerging ‘standard’ called Estuary English, although it may also occur as a type of speech defect or in the speech of very young children who have not acquired the standard pronunciation of yet.
Dental articulation in English is exemplified by the two fricatives /θ/ & /ð/, which often represent a problem for foreign learners, being replaced by either [s] & [z] or [t] & [d]. Some of these problems, however, may at least partially be due to the fact that some older textbooks used to describe them as interdental, a pronunciation that is not only fairly unrealistic (at least for British English), but also relatively difficult to achieve for the voiced variant... In most cases, the tip of the tongue makes a relatively firm contact with the bottom of the upper teeth and you should be able to feel the air flowing over the middle of your tongue before it hits the teeth.
The alveolar ridge, situated just above the upper teeth, is a highly popular place in terms of the production of English consonants. No less than 7 sounds are produced there, ranging from the plosives /t/ & /d/, including the nasal /n/, via the fricatives /s/ & /z/, to the two approximants /ɹ/ & /l/.
Sounds produced somewhere between the alveolar ridge and the hard palate are referred to a palato- or sometimes also post-alveolar. They include the two fricatives /ʃ/ & /ʒ/, as well as the two affricates /tʃ/ & /dʒ/.
The only English ‘consonant’ that is produced with a palatal articulation is /j/.
A velar place of articulation is limited to the two plosives /k/ & /g/, and their nasal counterpart /ŋ/.
Out of the two glottal sounds of English, we have already encountered one, namely the fricative /h/. The other glottal consonant is the plosive /ʔ/, also known as glottal stop. You can produce this sound if you create an abrupt constriction in your larynx, sort of like when you’re preparing to hold your breath.
The table below shows most of the consonants occurring in English, at least in the reference varieties. Where necessary and applicable, we will introduce further symbols when we discuss other accents of English or particular features that require their use.
Two further symbols for approximants that are not usually included in the consonant table are /w/ for the voiced labial-velar and [ɫ] and the velarised variant of the alveolar lateral /l/.
Catford, J. C. (2001). A Practical Introduction to Phonetics (2nd ed.). Oxford: OUP.
Fry, D.B. (1987). The Physics of Speech. Cambridge: CUP.
Johnson, K. (1997). Acoustic & Auditory Phonetics. Oxford: Blackwell.
Ladefoged, P. (1996). Elements of Acoustic Phonetics (2nd ed.). Chicago: University of Chicago Press.