Sound and noise

The difference between sound and noise often comes down to perception and context. Sound is a general term for vibrations that travel through the air (or another medium) and can be heard when they reach a person’s ear. Sounds can be pleasant, like music or a bird’s song, or neutral, like the hum of a refrigerator. In essence, sound encompasses all auditory experiences, whether they are enjoyable, neutral, or even unnoticed.

Noise is typically used to describe unwanted or disruptive sounds. It is often considered unpleasant or annoying, such as the sound of traffic, construction, or loud machinery. Whether a sound is considered noise can depend on the listener’s perspective and the context in which the sound occurs. For example, loud music might be enjoyable at a concert but considered noise if you’re trying to sleep. Essentially, all noise is sound, but not all sound is noise.

Perception of sound

When sound waves enter the outer ear, they travel through the ear canal and vibrate the eardrum. These vibrations are amplified by three tiny bones in the middle ear and sent to the cochlea in the inner ear. Inside the cochlea, the vibrations create waves in the fluid, moving the basilar membrane and stimulating tiny hair cells. These hair cells convert the vibrations into electrical signals, which are carried by the auditory nerve to the brain, where they are interpreted as sound.

Figure illustrating the ear and its basic components. ^{© Colourbox}

Measurements of sound

Sound is measured primarily in units called decibels (dB), which quantify sound intensity or loudness. The decibel scale is logarithmic, meaning each 10 dB increase represents a tenfold increase in sound intensity. For example, a sound at 20 dB is ten times more intense than a sound at 10 dB. The softest or weakest sound pressure level a normal human ear can detect is about 0 dB. At sound pressure levels above approximately 130 dB the sensory sensation is more associated with pain than sound.

^{© Colourbox}

In addition to decibels, sound can also be measured in terms of frequency, which is the number of sound wave cycles per second, measured in hertz (Hz). Frequency determines the pitch of the sound, with higher frequencies producing higher-pitched sounds. The normal human ear can detect frequencies roughly in the range 20 to 20 000 Hz.

These measurements help us understand and quantify the characteristics of different sounds we encounter in the work environment.

Using hand-held tools, such as this metal-cutter, generates both noise and hand-arm vibrations. ^{© Jessy Z’gambo}