The third part of the voice is the resonator. It consists, for the most part, of what is called the vocal tract, that is: the pharynx and mouth. The pharynx has three parts: the laryngeal pharynx, the oral pharynx, and the nasal pharynx. The nasal passages play a role in some vowels and consonants to be mentioned later. The sinuses are not resonators. It may feel as if they are but that is only sympathetic resonance and does not play a role in determining voice quality. Each singer has a unique set of sympathetic vibrations.
The harmonic series
Fundamental: A = 110 (this is the first harmonic)
2nd harmonic: A = 220
3rd harmonic: E = 330
4th harmonic: A = 440
5th harmonic: C # = 550
6th harmonic: E = 660
7th harmonic: G = 770 (will be flat, not used on brass instruments)
8th harmonic: A = 880
In the above example I am showing only one note, of course, A2, and its harmonics. There are 88 notes on the piano and each one has its own harmonic series. In all cases the harmonics are multiples of the fundamental. Also, I should mention here that we identify the notes on the piano, or in the voice the following way. The low A and B on the piano are, simply, A, and B. At C we add a number, in this case, C1. At the next C it becomes C2, etc. a good way to remember it is that A 440, the tuning A (above middle C) is A4. Middle C is C4. The tenor high C is C5 and the soprano high C is C6.
I will assume that you are familiar to some extent with overtones. These are the “tones over” the fundamental, the name for the pitch which is normally heard. If you play “middle C” on the piano, the strings will vibrate not only at C but at pitches higher than C. These will be an octave above C, a fifth above that, a fourth above that and so on in the harmonic series. What is happening is that the string vibrates in its full length, the two halves vibrate, producing pitches at half the frequency of the fundamental, i.e., an octave higher, those halves vibrate in half their lengths, and so on. Most musical tones are a complex set of vibrations of parts of the strings or resonance bodies (wind instruments).
To make the terminology of acousticians clear to you in case you do further reading, I would like to give you some definitions:
Fundamental: the frequency heard as “pitch;” referred to as F0
Overtone: a multiple of the fundamental; the first overtone is an octave above F0
Harmonic: same as an overtone but all the tones in a complex musical tone, including the F0, are harmonics. The first harmonic is, therefore F0
Partial: same as harmonics, however, we choose not to use the term because there can be non-harmonic partials which are undesirable. Therefore, in the interest of clarity we will stick to the term “harmonic” and not use “partial” or “overtone.”
Formant: a harmonic, or group of adjacent harmonics, that are stronger than average. Formants give instruments their characteristic tonal quality; it is how we distinguish an oboe from a trumpet; it is also how we distinguish individual voices.
One more explanation is necessary before we continue. You know how if you blow across the mouth of a bottle it will produce a certain pitch? That is because the confined space, such as a bottle or wind instrument has a certain volume and that volume resonates a certain frequency. If we disturb the air in a bottle or wind instrument, the frequency produced will correspond to the volume in that space. Only that frequency will vibrate. Think of the voice, with its two spaces, the mouth and the pharynx, as “bottles” which will resonate certain frequencies. These are formants. Any disturbance of the air in the vocal tract will produce the formants: speaking, singing, whispering, and even tapping the cheeks.
Vowels are produced by a combination of two formants. This strength in two harmonics is heard by the listener as a vowel; we learn this as we learn to speak. We learn to hear vowels and we learn to make them.
The speaking voice tends usually, except with some classically trained actors and preachers, to have only two formants and not to have harmonics much in excess of 2500 Hz. The classical singing voice, however, has harmonics going up to 4000 Hz and beyond and has three more formants above the vowel defining ones. These are often grouped together under the term “singer’s formant.” It consists of a high, bright “ring” in the voice and is characteristic of a well-trained “classical” voice. It is what gives the voice its strength and carrying power.
Returning for a moment to the closure of the vocal folds, which were mentioned earlier, when there is a good closure, that is, when the vocal folds are closed for more than 50% of the vibratory cycle, the resulting sound is rich in harmonics, often going as high as 10,000 Hz. With this “raw” material, the vocal tract is able to strengthen some harmonics and to attenuate (weaken) others.
What about the “singer’s formant?” If the sound produced in the larynx is rich in harmonics, the singer’s formant will be present. There are theories about where in the vocal tract this formant is enhanced. Voice researchers have observed x-rays of singers making a big, ringing sound, one with 3000Hz harmonics in it—the “singer’s formant.” What they see is that the collar of the larynx, that is, the opening into the pharynx, is one-sixth the size of the pharynx (the part of the “throat” from the larynx up to the soft palate.) How do we make this happen? We can’t feel anything down there and, in fact, we must not try to manipulate it.
For the pharynx to become large enough to be six times bigger than the opening of the larynx, we must learn to relax the muscles at the back of the throat that constrict the pharynx during swallowing.
Learn to hear the “ring” in the voice and to adjust the vowels very minutely until this ring becomes clear and predictable. We must train the ear to hear it and, to some extent the ear will guide the voice.
This excerpt is from Winston Purdy’s untitled unpublished book on Singing Technique