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What is sound?

In reporting we are processing measured sound data into numbers and present them as tables and figures. This way the reader can see, e.g., the sound pressure levels at different measurement points. But what is sound really? What are the units we use to describe it?

At its simplest, sound is a pressure wave created by a vibrating object. When we think of sound, we usually think of pressure waves travelling through air. Our ears, together with our brains, convert the pressure change into an auditory sensation and allows us to recognize the sound. Decibel (dB) is used as a unit of sound pressure level and it describes intensity of the sound level. Humans can hear sound between 0 to 140 dB. The zero level is set at a level that is generally considered the threshold of hearing for humans. This is the level to which the other sounds are compared to. For example, a normal discussion at the office ranges from 50 to 60 dB, the sounds from the busy highway can have sound levels between 70 to 80 dB and at a rock concert the sound level can be around 85 dB. Pain threshold is at 130 dB.

In our work, we hear vast range of sounds. The sounds of nature vary through seasons: in spring the birds are singing, in summer the leaves are rustling, in autumn the rain is falling and in the winter the trees are cracking under the extreme temperatures (at least here in Finland). Sounds created by humans range from the normal sounds of living to sounds of traffic such as cars, motor bikes and air planes. Below you can listen to different sounds. They are recorded with our Aures 3.0 Logger which is designed to measure environmental noise but it can also be used to measure the indoor sound.The example sound clips have the same sound level, therefore, allowing you to hear the differences in the sound pressure levels due to the sound source. Can you hear the difference?

Until the next post,


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