The Relationship Between Hertz and Decibels

By Eric Blankenburg

Vibrating objects create waves of energy that change the pressure of the surrounding air. These pressure changes are picked up by the human ear and interpreted by our brains as sound. The waves of energy produce alternating positive and negative changes in air pressure, known as oscillations, which can be measured in Hertz and decibels.

Sound Frequencies

When an object vibrates, the alternating positive and negative pressure creates a wave, also known an oscillation. A complete oscillation is measured in the frequency of waves per second. Hertz is the standard unit of measurement used to calculate the frequency of these oscillations. If one oscillation occurs in one second, the frequency is denoted as 1 Hertz. When 500 oscillations occur in one second, the frequency is denoted as 500 Hertz. An average, healthy person can hear sounds that range from 20 to 20,000 Hertz.

Pressure Changes

Humans hear vibrational energy -- or the changes in air pressure -- as sound. An object is perceived to be louder or quieter depending on the amount of air pressure generated by the vibrating object. This pressure changes regularly and dissipates for the listener as his distance increases from the source. Air pressure changes can also be measured in units of Pascal, but since these numbers are often very large and hard to work with, the decibel is now more widely used.

Sound Levels

The average, healthy human can detect sounds at the zero decibel level, but a person with really good hearing can detect sound at -5 decibels. The sound level, perceived by the ear, is based on the level of sound pressure and the pitch of the sound; certain frequencies of pitch are easier for the human ear to detect.

Hertz and Decibels

The relationship between Hertz and decibels allows a listener to measure the frequency and perceived loudness of any sound. The frequency or amount of air pressure change vibration is measured in Hertz. The resulting change in air pressure created through the vibrating object is measured in decibels. Decibels, in effect, measure the loudness of a sound and Hertz measures the frequency of the sound.