Anatomy of the Voice
Most people don't really take any time to consider the interesting work that goes on in the body when they sing. They seem to assume that the voice just magically 'appears' whenever they will it to.
Nearly everyone has probably heard expressions like 'sing from the diaphragm (or belly)' and 'support the breath (or voice)', used frequently by many singing teachers. However, if a student doesn't understand some basic human anatomy that is related to making breath and sound, these common expressions can become encased in mystery.
While a teacher is an invaluable resource to a student, the student must also take responsibility for his or her own progress, which includes learning about the voice. A student of voice cannot possibly learn how to achieve greater control over his or her singing voice if he or she does not understand the physiological mechanisms to which his or her teacher is referring. It isn't necessary to memorize all the complex parts and functions of vocal anatomy, but it is helpful to gain a general and practical understanding of them. Comprehending the terminology (e.g., diaphragm, support, intercostal muscles, resonance, hard palate, placement, etc.) that a teacher uses during lessons will help vocal students make more consistent progress.
Vocal technique is as much a science as singing is an art form. While, initially, a student may have to concentrate very hard on his or her breathing, tone placement and muscle control, these techniques will become easier, more natural and even automatic in time, making singing much more enjoyable.
THE PHYSICS OF BREATHING
Needless to say, effective breathing technique is essential to good singing. Part of the process of studying voice is developing an acute awareness of the actions involved in breathing and exploring them in depth. A teacher is essential to helping a student gain control and thus confidence and trust in his or her own breath, and to guide him or her toward a greater understanding of the potential that breath carries for him or her as a performer.
The mechanism of breathing can be summarized in this way:
Receiving various signals from the nervous system, the diaphragmatic muscles contract and the diaphragm moves downward. As the diaphragm depresses, it creates a vacuum in the lungs and air rushes in to fill that vacuum. During exhalation, the diaphragm relaxes and rises and lung volume decreases, creating a positive pressure difference, and air rushes out.
For a more in depth look at the mechanism of breathing and how correct breathing technique enhances singing, and for some exercises to help improve how you use and support your breath, read Correct Breathing For Singing.
DIAPHRAGM
The (thoracic) diaphragm is a shelf of muscle and tendon that extends across the bottom of the ribcage, dividing the torso in two. Above is the thorax (chest), with the lungs and heart, below is the abdomen. It is dome-shaped, slightly higher on the right side, and curves up toward the centre. It features a boomerang-shaped central tendon - the aponeurosis - which is connected all around by muscular fibres that originate on the lumbar spine, the bottom edge of the ribcage and sternum (breastbone).
The heart, which is attached to the diaphragm via its pericardium - a membrane sac that envelops the heart - moves up and down with the diaphragm.
LUNGS
The lungs are made of a soft, elastic, spongy tissue. Their structure is much like an inverted tree. Air enters the lungs via the trachea (the "trunk"). The trachea branches in two to form the bronchi. Each bronchus continues to branch out into bronchioles until, at the end of each bronchiole, a cluster of alveoli, which are small sacs where gas exchange of carbon dioxide and oxygen takes place, is reached. The total surface of the alveoli is very large.
As the ribcage and diaphragm move, the lungs are stretched, drawing air into the lung (inhalation), or the lungs are compressed, pushing the air out (exhalation).
MUSCLES
Most students of voice don't consider the importance of the support structure for the voice, yet the muscles of the back and abdomen aid the diaphragm and lungs in establishing the movements necessary for breathing.
The intercostal muscles are found between the ribs, and there are two kinds: The internal intercostal muscles (in the inside of the ribcage) extend from the front of the ribs, and go around the back, past the bend in the ribs. In front of the ribcage, looking from the bottom of each muscle (i.e. the top of each rib), the muscles go diagonally inward. The external intercostal muscles (on the outside of the ribcage) wrap around from the back of the rib almost to the end of the bony part of the rib in front. They go downward and outward when viewed from the back. (At the bottom of the sternum can be seen the transversus thoracis muscle.) These muscles can be felt during coughing.
Having the muscles on diagonals increases the amount of work that they can do, since a longer muscle can become shorter upon contraction than can a shorter, vertical muscle, as it contracts along the full length of the muscle fibres.
When proper diaphragmatic breathing technique is employed, and when a singer's endurance is being tested, the intercostal muscles can get a very good workout. Muscle fatigue is especially common amongst new vocal students who haven't yet built up strength in these muscles and are isolating them during singing for the first time.
THE ABDOMINAL MUSCLES
Often mistakenly called the diaphragm by singers and by some teachers, the abdominal muscles are linked with the breath when they are used to "support the breath" or when they stretch as the belly distends due to the action of the diaphragm.
The deepest of the abdominal muscles, the transversus abdominis, go horizontally from front to back. They are very important in respiration, and are probably instrumental in forced exhalation.
The external obliques course downward and inward, and are the largest and strongest abdominal muscles. These muscles work posturally by contracting and may flex or twist the spine. By compressing the abdomen, these muscles create higher pressure in the abdomen and thorax (chest), essential for forced expiration. Also, by relaxing these muscles, one can allow the distention of the belly to be more free, making the action of the diaphragm more easily felt.
Sandwiched in the middle between the external obliques and the transversus abdominis are the internal obliques. Their direction is down and out, or the opposite of the external obliques. They can be used to compress the abdomen for exhalation.
MUSCLES OF THE LOWER BACK
The muscles of the lower back are often overlooked by those studying voice. While some of these muscles are primarily flexors of the lower limb (i.e., thigh and pelvis), the quadratus lumborum serves as the equivalent muscle of exhalation to the abdominal muscles found in front. The psoas major, a long muscle on the side of the lumbar region of the spine and brim of the pelvis (in front of the hip joint), connects with the muscles of the diaphragm.
In terms of respiration, the quadratus lumborum can be felt to stretch most easily when the abdominals in front are contracted and one "breathes into the lower back", allowing the diaphragm to push the organs of the abdomen against these muscles. On contraction, they serve as muscles of exhalation. They may also hold the lowest part of the ribs in place during inhalation, allowing the diaphragm to drop down more effectively.
SUPPORT
Support works by contracting the abdominal muscles, creating higher pressure in the abdomen and thorax, allowing the diaphragm's relaxation (and upward rise) to be more carefully controlled. There is less control in relaxing a muscle than there is in contracting it, so support gives performers a means of controlling their sound, or phonation.
Today, there are two main schools of teaching about the breath, although there are many different approaches: "supporting" the breath by compressing the abdomen during phonation (i.e., on the exhalation), or relaxing the abdominal muscles as much as possible during inhalation and phonation, allowing the diaphragm to work on the inhalation, and riding its relaxation on the outgoing breath (i.e., during phonation).
The extent to which action of the ribs is encouraged varies within most techniques, although most teachers, including myself, recommend that the upper torso, especially the shoulder girdle, be as relaxed as possible even during the most extreme vocal demands. Ultimately, a singer wants access to all the "breath resources" available without jeopardizing the ability to freely produce sound, that is without unnecessary tension.
I have dedicated an entire article to Correct Breathing For Singing, also published on this site, that gives singers a more comprehensive look at ideal (diaphragmatic, including appoggio) breath management techniques and incorrect and unhealthy breathing techniques, as well as practical exercises to learn better support of the tone.
THE PHYSICS OF MAKING SOUND
When air is expelled from the lungs, it rises up the trachea and runs into constriction at the larynx - where the vocal cords, now called vocal folds, are housed - causing the vocal folds to vibrate or buzz. This buzzing quality to the speech is called voice or voicing. The vocal folds 'chop' the air stream up into a series of rapid 'puffs' that create the sound. (It isn't the impact of the folds coming together that makes the sound.) This produces a fundamental tone frequency, (the lowest frequency in a harmonic series), accompanied by several non-harmonic overtones, (a natural resonance or vibration frequency of a sound system).
The resulting sound is modified by movements in the vocal tract, (where sound that is produced at the larynx, pharynx, and oral and nasal cavities is altered), by the volume of the airflow and by the degree of constriction of the vocal folds. (During speech the flow of air is relatively small because of constrictions of the vocal folds.)
The vocal vibration is varied to produce intonation, (the variation of pitch to express emphasis, contrast, emotion, etc.), and tone, (the use of pitch in language to distinguish words). This is accomplished by varying the pressure of the air column under the glottis, (the space between the vocal folds, located in the middle part of the larynx), as well as the tension in the vocal folds themselves. These actions produce changes in the frequency of vocal-cord vibration, which generates the fundamental pitch of the voice.
RESONATION (VIBRATION)
The buzz created by the vocal folds resonates (vibrates) the air column and this, in turn, causes the structures above and around the larynx to vibrate, as well.
The parts of the body that can vibrate in harmony with the voice are often called resonators, which include the air column and formants (see section on formants below).
The following areas vibrate 'sympathetically' with the air column. The way in which each area vibrates acts as a cue to the quality of the sound created, giving tactile motor feedback to the brain, which works in conjunction with the hearing mechanisms. The following is a list of resonators and the pitches or vocal qualities that most easily activate them:
Chest and Lower Body - low pitches and open sounds, like 'ah'
Throat - mid-range, easy speaking tone
Mouth - upper mid-range, mid-vowels
Nasal - closed, front vowels, especially when followed by a nasal consonant such as 'n' or 'm'
Facial - high range, front vowels
Sinus - Given that there are so many sinuses, many different quality sounds activate them
Bones and Skull - falsetto and head voice, very high range, closed vowels.
'Placement' of the voice generally describes how the vibration of the air column interacts with these structures to accentuate or diminish the size of the formants (see below). The term 'placement' indicates where one feels the augmented vibration due to the change in the relationship of the formants to areas of the body.
Extending from the larynx to the lips, the air column vibrates at a natural frequency - in much the same way that the pipes of an organ do. As the organ pipe is shortened, and thus the air column, the pitch gets higher. In speech, the rate of vibration of the vocal folds creates the fundamental frequency, or pitch of the sound. This frequency determines the musical pitch or note that is created by vibration over the full length of the air column. The frequency (or frequencies) at which the air column vibrates determines the quality of the tone.
The sound created by the vocal folds isn't a pure tone - it's complex. It is made up of the fundamental frequency, (the rate at which the folds vibrate), and a number of partials, which are harmonics of the fundamental frequency, vibrating two times, three times, etc. as fast as the fundamental. The voice is made up of a spectrum of the fundamental and these 'overtones', or formants - see below. The lowest possible frequency and such multiples form the harmonic series.
Vocal resonation is explained more fully in Good Tone Production For Singing.
FORMANTS
In phonetics, formants are the distinguishing or meaningful resonant frequency components of human speech and of singing. They appear in spectrograms as peaks in the harmonic spectrum of the voice.
We distinguish between vowels - sounds in spoken language that are characterized by an open configuration of the vocal tract so that there is no build-up of air pressure above the glottis - by the frequency content of the vowel sounds. (This contrasts with consonants, which are characterized by a constriction or closure at one or more points along the vocal tract.) Formants are the characteristic partials that identify vowels to the listener. Most of these formants are produced by 'tube and chamber' resonance.
Since the larynx closes off at the bottom during phonation, it naturally resonates at the odd numbered multiples of the fundamental. These 'standing-waves' of sound are also known as formants. In shaping speech, the first three formants are the most important. In a way, it is as if each vowel is a 'chord', like playing three notes together on the piano, where the bottom note stays the same and the notes above change.
What we recognize as vowels are actually changes in the quality of the tone. Our tongues allow us to change the shape of the 'tube', specifically changing the cross-sectional 'width' by sliding forward and back. Lip rounding essentially lengthens the tube.
If the fundamental frequency of the underlying vibration is higher than the formant frequency of the system, the character of the sound imparted by the formant frequencies will be mostly lost. This is most apparent in the example of soprano opera singers, who sing high enough that their vowels become very hard to distinguish.
More detailed information about formants can be read in Good Tone Production For Singing, which explores formants in general, including the Singer's Formant, Singing With An 'Open Throat': Vocal Tract Shaping, which covers the topics of how formants affect tonal balance and quality and how to encourage the presence of these upper harmonic partials in the voice (through formant tuning and formant tracking), and Vowels, Vowel Formants and Vowel Modification, which examines the 'fingerprint' formants of specific vowel sounds.
(Control of formants is an essential component of the vocal technique known as overtone singing, in which the performer sings a low fundamental tone, and creates sharp resonances to select upper harmonics, giving the impression of several tones being sung at once. There are many styles of this singing technique, including the chanting of the Tibetan Monks)
PHONATION (MAKING SOUND)
Phonation refers to the use of the laryngeal system to generate sound - an audible source of acoustic energy - which can then be modified by the articulatory actions of the rest of the vocal apparatus (see section on articulation below).
Sound is generated in the larynx - an organ in the neck involved in the protection of the trachea and in sound production. The larynx houses the vocal folds, and that is why it is commonly referred to as the 'voice box'. It is situated just below the pharynx - the part of the neck and throat situated immediately behind the mouth and nasal cavity and cranial, and above the esophagus, larynx and trachea (the "windpipe").
The larynx is also where pitch and volume are manipulated. The strength of expiration from the lungs contributes to loudness, and is necessary for the vocal folds to produce speech.
Understanding the complex anatomy and physiology of the larynx is quite an undertaking. Control of the laryngeal muscles is done through a biofeedback process involving sensing and monitoring the vibration of the vocal folds through the sound and feeling that it creates. Learning to make adjustments to those actions is a complex and slow process - one that takes a lifetime to master. Any knowledge about the structures that create those sounds and feelings can only help a singer to appreciate and analyze what is being felt and heard. I have written a detailed article on the structure and function of the larynx itself that will provide more insight into how sound is generated and controlled by the laryngeal mechanism. In Singing With An 'Open Throat': Vocal Tract Shaping, a diagram of the larynx, as well as information about the ideal position of the larynx during singing, can also be found.
ARTICULATION (THE FORMATION OF SPECIFIC SPEECH SOUNDS)
Finally, air and vibration pass through the vocal tract and are shaped by the articulators into recognizable speech sounds.
Movable articulators are structures that can move and allow us to shape the sound, (i.e., the jaw, the lips and other facial muscles, the tongue, the soft palate - the soft, movable tissue constituting the back of the roof of the mouth - and the pharynx).
Fixed articulators are those that cannot be moved by muscles, namely the hard palate and teeth. The hard palate is a thin, horizontal bony plate of the skull, located in the roof of the mouth, which spans the arch formed by the upper teeth. It forms a partition between the nasal passages and the mouth. (This partition is continued deeper into the mouth by the soft palate.)
The article entitled Singing With An 'Open Throat': Vocal Tract Shaping, also posted on this website, explains the process of articulation in greater detail, as well as how assuming specific articulatory postures directly affects the tone and health of the voice.