Dennis Haines, age 16, of White Plains, N.Y., for his question:

JUST WHAT IS A DECIBEL?

A decibel is the unit used to measure the intensity of a sound. A decibel is a tenth of a larger unit, the bel, which was named for

Alexander Grahm Bell, the inventor of the telephone.

The decibel is not the unit of loudness. Loudness is often measured in phons, which depend on both the intensity and the frequency of sound. Frequence is the number of vibrations per second.

The intensity of a sound depends on the energy it produces. The energy of sound is usually given in watts per square centimeter. As a decimal fraction, the sound of 0 decibels is written 0.00000000000000001 watts. Zero decibels is about the least intensity of sound that the normal ear can hear.

A sound of 10 decibels, or 1 bel, transmits ten times as much energy as an 0 decibel sound. A sound of 20 decibels transmits a hundred times as much energy as a 0 decibel sound and 10 times as much as a 10 decibel sound.

Ordinary speech measures approximately 60 decibels.