Vocal resonance. The vocal tract
Resonance represents the tendency of an object or system (like the air contained by the vocal tract) to respond (oscillate) more strongly to particular frequencies introduced into it. The vocal tract is essentially an airspace resonator made up of a series of interconnected ‘chambers’, each with its own resonance bandwidth.
The four main regions of vocal tract resonance are the pharynx, the nasal and oral cavities and the epilarynx.
The pharynx or pharyngeal tube is situated immediately above the larynx extending upward behind the mouth and nose. It represents the largest and most important resonator for the voice; it is so near to the larynx that it has the first and most potent effect upon tone quality. For convenience, it is divided into three parts: laryngopharynx, oropharynx and nasopharynx.
During singing, the pharynx must be open and free of constrictions; this concept is known as ‘singing with an open throat’. The pharynx, when it is relaxed and large enough, gives mellowness and fulness to the vocal timbre, the desired strategy, especially for classical singing.
Contemporary music genres use different types of tone qualities and voice production techniques. One can play with tone quality by shaping the pharyngeal tube. The muscles inside the pharynx can be used to narrow or widen parts of the pharynx, to alter the resonating quality. The resonating space can be modified by arching or pulling the soft palate horizontally. The length of the pharyngeal tube can also be adjusted by lowering or raising the larynx. A raised larynx lengthens the pharyngeal tube, and by doing so, it gives a perceptually brighter resonating quality. Similarly, a lowered larynx shortens the pharyngeal tube and gives a deeper resonating quality.
What it is of crucial importance is that every time a vocal tone is employed, the pharynx needs to be free of constriction, so hurting the voice is avoided.
The nasal cavity
The nasal cavity and the oral cavity are separated by raising the soft palate (velum). A lifted soft palate closes off the access of the air through the nose.
When singing non-nasal consonants and all non-nasalised vowels, a lifted velum is a necessary action. Lowering the soft palate will open the nasal cavity, allowing the pronunciation of nasal consonants like m, n and ng. If applied to other sounds, it will be giving a perceptual nasal sound quality.
The nasal cavity is full of soft tissue, and this makes it a rather inefficient resonator. However, because technology allows us access to microphones and amplification tools, one is no longer constricted in using nasal sound quality. Commercial singers nowadays mix in a little nasality if it suits a specific character they what to express or for vocal effect.
There are a few ways of telling if someone is singing or speaking nasally. One is by holding a mirror under the nostrils when making sound and observing how much it clouds – meaning how much air escapes through the nose. Another is by plucking one’s nose when producing non-nasal vowels and noticing if the sound changes quality. When this happens, it means that again, some air escapes through the nose and alters the timbre quality in a muffled direction.
The oral cavity
The mouth or oral cavity runs from just behind the lips to the arches at the back of your mouth called de facial pillars. The soft palate at the top, the pillars at the sides and the tongue at the bottom, mark the boundary between the mouth and the pharynx. The soft palate, the tongue and the jaw can act together or independently to shape the resonating sound quality.
The position of the tongue determines whether the mouth and throat will function principally as a one large air chamber or whether there will be two resonators. Also, because the tongue is a big and strong muscle and directly attached to the hyoid bone will have a significant impact on vocal comfort and resonant quality. Here are some tongue postures encountered in singing and their impact on sound quality:
- A high and forward tongue body (as in making an ‘EE’) will favour a brighter sound.
- A rearward tongue body (as in making an American ‘r’) will tend to give a darker or ‘covered’ sound quality.
- A tense tongue root that sinks back and down in the throat will narrow the pharynx and is most likely to produce a perceptibly throaty or muffled sound quality.
The jaw or mandible forms the side and front boundary of the oral cavity. The opening of the jaw impacts the resonating quality in the sense that a wider opening of the jaw will actually reduce the resonating space in the oral pharynx area. Any adjustments made towards a bigger space must take into account the size and shape of the resonating chambers further back and down the vocal tract.
The lips are mostly used in forming vowels and consonants, but they can also slightly alter the length of the vocal tract. Lip protrusion will lengthen the vocal tract and lep widening will shorten it, lowering or raising all the resonance frequencies respectively.
The part of the larynx between the vocal folds and the epiglottis is sometimes referred to as the epilarynx. This funnel-shaped tube begins at the base of the cricoid cartilage and includes the muscles between the arytenoids at the back of the larynx, the epiglottis and the muscles around that. When the muscles around the epiglottis contract, they will narrow the tube in an anterior-posterior direction (front to back).
A narrowed epilarynx gives a brighter, perceptually ‘twangy’ sound that will boost the sound levels of your voice. Opera singers use this narrowing, coupled with a widened and elongated pharynx, to create the ‘singer’s formant’, a special clustering of resonance frequencies that allows them to project acoustically through a full orchestra.