Introduction to Acoustics for Vocalists

Matthew Reeve

Acoustics is the science of sound. Knowing a little about the fundamentals of this science can give the vocalist insights into how the voice functions. All sounds can be understood and analysed in the simple terms power, source and filter. The voice, essentially an acoustic instrument, can be explained in these terms.

Sound is generated when air is displaced, causing variations in air pressure. The variations then travel through the air as sound waves. These variations of air pressure are then picked up by the ear and decoded by the brain. Something has to move or vibrate to cause the air to be displaced. Movement energy, or kinetic energy, is changed to acoustic energy. The environment can affects the sound waves as they travel to the ear.

Power, Source and Filter

1. Clap your hands once, palm to palm. A sound is generated. Ask yourself the following questions. What moved and what caused it to move? Where did the sound begin? What influenced the sound before it reached your ear?
2. Drop a book on the floor. A sound is generated. Ask yourself the same questions.
3. Blow a raspberry through your lips. A sound is generated. Ask yourself the same questions.
4. Make sounds by flicking your fingers against the side of the neck. It is important that you hold your breath while you do this and keep your mouth open. Now change the sound by altering the position of the tongue and lips as in shaping vowels. Ask yourself the following questions. What moved and what caused it to move? Where did the sound begin? What influenced the sound before it reached your ear?
5. Now speak the same vowels normally. Ask yourself the same questions.

In these exercises, in addition to the properties of moving object, the room itself has an effect on what the ear hears. For instance, if you were to fill the room with lots of soft furnishings the sound would be very different from if the room was completely empty.

Whether it is muscle energy in your hands, the forces of gravity or the small muscles in your fingers, energy is needed to power the sound. This generates the necessary kinetic energy that causes the displacement of air particles and, in turn, the variations in air pressure. The point where this happens is the source. The quality of sound is determined by the properties of the sound source and the environment between the sound source and the ear. This environment is known as the filter.

In phonation, the breath is the power of the voice. The muscles of expiration and elastic forces in the lungs create the power. The vibrating vocal folds are usually the source of the voice. The vocal tract is the main filter of the voice. Many structures in the vocal tract are not fixed in one position and they can be moved around, changing the shape and properties of the filter. This is a unique feature of the vocal instrument.

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