What is a Sound Level Meter ?

Sound level meters look quite simple. They have a pointy stick at the top, which is the microphone that samples and measures the sound. The stick keeps the microphone away from the body of the sound level meter itself, cutting out reflections, and giving a more accurate measurement. Inside the square box at the bottom of the meter, electronic circuits measure the sound detected by the microphone and amplify and filter it in various ways before showing a readout on a digital LCD display.

1. Noise Exposure

2. The volume alone can't always tell you whether the sound in a particular place is dangerous. Some sounds are quiet enough to be safe in small doses but loud enough so that they will damage your hearing if you listen to them for long enough. Because of this, sound level meters used to measure sound safety have a feature called logging. These sound level meters record the sound level over a long period of time and come up with an average sound level. If the average sound is too high, the sound level is not safe. This function is known as LEQ and is normally found in more expensive Work Place Sound Level Meters

The Decibel Scale

You have to think about the decibel scale very carefully, because it's a logarithmic scale and it works in a different way to the scale on a ruler, which is a linear scale. On a ruler, a distance of 20cm is twice as long as a distance of 10cm and 30cm is three times as long. But the logarithmic decibel scale goes up in powers of ten: every increase of 10dB on the scale is equivalent to a 10-fold increase in sound intensity (which broadly corresponds with loudness). That means a sound of 20dB is 10 times louder than a sound of 10dB and a 30dB sound is 100 times louder. A sound of 100dB is actually 1,000,000,000 times louder than a sound of 10dB and not 10 times as loud, as you might suppose. That's why sounds high up the decibel scale (from about 85-200dB) are a major cause for concern: the sounds waves carry so much energy that they will damage your hearing, sooner or later

Excerpts from ExplainThatStuff.com