WHAT are decibels?

A decibel is the unit for measuring the intensity, or loudness, of a sound. Today it is possible to study noise scientifically by means of electrical instruments. Chief among these is the sound meter, or noise meter, a device that changes sound into electrical signals and then measures the signals in terms of decibels. One decibel is about the smallest difference of sound intensity that the normal human ear can detect. Twenty decibels mark sound one hundred times as strong as a ten decibel sound. Thirty decibels mark sound a thousand times as strong as a ten-decibel sound, and so on.

A man’s heart beat creates a sound of a little more than 10 decibels. The purring of a cat is about the same as a whisper 25 to 30 decibels. A single typewriter accounts for 40 decibels.

A few other common noises are rated in decibels as follows:

• Barking dog-65;
• Piano practice-75;
• Average motor truk-80;
•  Loud shouting-85;
• Pneumatic riveter-105

All noises above 130 decibels are actually painful in our ears.

The noise of city streets ranges from 50 to 85 decibels. The country noise level is about half that of the city. It should be remembered, however, that a large volume of steady noise in the city actually seems less than a series of lesser country noises coming at random after intervals of comparative silence. The cricket and katydid, the locust and bullfrog and the mournful whippoorwill often strike the attention to a degree out of proportion to the noise they make. Just so the sudden slamming of a door and the unexpected ringing of a telephone bell are more of a menace to sleep or concentration than the continuous roar of traffic, loud as it may be. Homer says that stentor (source of our word “stentorian”), famous in the Greek army for his loud voice, could equal the combined voices of 50 men. His shout was probably on a decibel level of 100.