Understanding Sound: Properties, Production, and Human Perception
Sound: Creation and Characteristics
Sound is produced by the vibration of bodies. In some cases, these vibrations are observable with the naked eye.
What is Sound?
When a body vibrates, it causes buoyant air particles to collide, compressing them and increasing their pressure. Shortly after, the opposite effect occurs: the air particles separate, reducing the pressure and causing rarefaction.
The vibrations of the membrane are transmitted to the air in the form of compressions and rarefactions of its particles, which we call sound waves. The energy that produces the vibration is transmitted to the air in the form of sound waves. Sound is the propagation of vibrations of bodies through a material medium.
Qualities of Sound
Intensity
The intensity of a sound depends on the energy with which the source that generates it vibrates.
- If a small amount of energy is communicated, a weak sound will be heard.
- If a large amount of energy is communicated, the same tone of sound will be heard, but stronger.
Sound intensity is measured using the decibel scale. One decibel is the least perceptible sound, and 120 dB corresponds to the pain threshold. An oscilloscope is used to study sound. Similar to a television, it captures sounds with a microphone and transforms sound waves into an electrical signal displayed on the screen. The height of the wave, or amplitude, measures the intensity of sound.
Tone
The tone of a sound is determined by its frequency. Sound is produced when bodies vibrate, but not all vibrate at the same speed; some vibrate more slowly, and others more quickly.
- When they vibrate rapidly, with high frequency, they emit high-pitched sounds.
- When they vibrate more slowly, with lower frequencies, they emit low-pitched and bass sounds.
The frequency of a sound is measured in oscillations that occur every second; its unit is the hertz (Hz).
Timbre
Timbre is the quality that allows us to distinguish two sounds of the same intensity and tone from different instruments. Diapasons emit pure tones (one frequency), but any other instrument (including the human voice) simultaneously produces a mixture of various sounds.
The Human Ear
External Ear
The external ear consists of the pinna (ear) and the auditory canal. Its mission is to direct vibrations from the outside to the eardrum.
Middle Ear
The middle ear begins at the tympanic membrane, which vibrates when it receives changes in air pressure. Attached to its center is a chain of ossicles that transmits vibrations to the inner ear. It transforms the movement of the eardrum into small vibrations of the liquid that fills the inner ear. The middle ear communicates with the outside via the Eustachian tube, which serves to balance the pressure differences on both sides of the eardrum.
Inner Ear
The inner ear is the most complex part of the ear. It is formed by a series of channels rolled into a spiral, filled with liquid and separated by membranes, where hair cells are located that receive nerve endings. Sound waves stimulate the hair cells, and therefore the endings of the auditory nerve, causing nerve impulses that are transmitted to the brain, which produces the sensation and interpretation of sound.
Audible Sound Range
Can we hear all sounds? No. Nature produces sounds that humans cannot hear. The sounds we can hear are between 20 and 20,000 Hz. To capture very low or very high-pitched sounds, they must be very intense.
Some animals can hear sounds above 20 kHz (ultrasound). Modern technology uses ultrasound for sonar and medical imaging.
