Glossary

Decibel (dB):
is the unit used to measure the intensity of a sound. Strictly, dB is a unit of ratio; 10dB is ten times louder, whilst 20dB is 100 times and so on. However, in the noise, sound and audio worlds it has come to be used to denote sound pressure level. The decibel scale is used because the human ear is incredibly sensitive and its perception of changes in loudness is approximately proportional to dB or ratio.

Your ears can hear everything from your fingertip brushing lightly over your skin to a loud jet engine. In terms of power, the sound of the jet engine is about 1,000,000,000,000 times (120dB) more powerful than the smallest audible sound. That's a big difference!

Our hearing is more sensitive to some frequencies than others, as is the susceptibility to damage. The standard used to take account of this is known as A-weighting. Measurements for sound intensity are therefore denoted dBA. It is important to be precise when stating such parameters.

On the decibel scale, the smallest audible sound (near total silence) is 0 dBA. A sound 10 times more powerful is 10 dBA. A sound 100 times more powerful than near total silence is 20 dBA. A sound 1,000 times more powerful than near total silence is 30 dBA. Here are some common sounds and their decibel ratings:

Near total silence - 0 dBA
A whisper - 15 dBA
Normal conversation - 60 dBA
A lawnmower - 90 dBA
A car horn - 110 dBA
A rock concert or a jet engine - 120 dBA
A gunshot or firecracker - 140 dBA

You know from your own experience that distance affects the intensity of sound - if you are far away, the power is greatly diminished. When comparing noise sources it is necessary to specify the distance. All of the ratings above are taken while standing near the sound.

There is a second measure of sound intensity dBC. This C-weighting characteristic is used to measure peak intensities rather than the average intensities of dBA.

Any sound above 85 dBA can cause hearing loss, and the loss is related both to the power of the sound as well as the length of exposure. You know that you are listening to an 85-dBA (approximately) sound level if you have to raise your voice to be heard by somebody else standing 6 feet away. Eight hours of more than 85-dBA sound can cause damage to your ears; any exposure to 140-dBC sound causes immediate damage (and causes actual pain!)

Noise Attenuator:
A device that is inserted into your ear to "attenuate" (reduce) the level of sound that is reaching your eardrum. It may range in complexity from a simple disposable "Earplug" (available from your nearest chemist shop for a few pence) which can be made from foam or even wax, to custom fitted ear moulds with flat frequency response, attenuating diaphragms. Simple earplugs will protect your hearing, but because they attenuate high frequencies more than low frequencies, they severely reduce the intelligibility of conversation or music. A much better solution is to use an attenuating earplug either in generic form, (commercially available as Elacin ER20) or, better still, a custom fitted hearing attenuator.

Noise Induced Hearing Loss:
NIHL can be caused by a one-time exposure to an intense "impulse" sound such as an explosion, long periods of moderate sound levels e.g. working in a noisy bar, or by continuous exposure to loud sounds over an extended period of time, such as working in a live music environment for long periods.

Threshold Shift:
A protective mechanism of the ear in response to loud sounds – it literally "turns down the gain" of the hearing mechanism effectively resulting in temporary partial deafness.

If you have ever been subjected to loud noise (for example at a live music event) you will be familiar with the "slightly deaf" feeling afterwards. The effects usually disappear after a day or so, but the damage has been done – remember, noise induced hearing loss is a cumulative effect and one day you will pay for that loud gig!