Decibels

Definition

Decibels (dB) are a logarithmic unit used to measure sound intensity levels. They express the ratio of a particular sound intensity to a reference level, usually the threshold of hearing.

5 Must Know Facts For Your Next Test

1. Decibels use a logarithmic scale, meaning an increase of 10 dB represents a tenfold increase in intensity.
2. The reference level for sound intensity in air is typically $10^{-12}$ W/m².
3. The formula to calculate decibels is $L = 10 \log_{10}(I/I_0)$ where $I$ is the sound intensity and $I_0$ is the reference intensity.
4. A sound level of 0 dB does not mean there is no sound; it means the sound intensity is equal to the reference level.
5. Human perception of loudness roughly doubles for every increase of about 10 dB.

Review Questions

• What is the reference level of sound intensity in air when measuring decibels?
• How much does the intensity increase if the sound level increases by 20 dB?
• Explain why decibels are considered a logarithmic scale.

Related terms

Sound Intensity:

The amount of energy carried by sound waves per unit area, measured in watts per square meter (W/m²).

Logarithmic Scale:

A nonlinear scale used when there is a large range of quantities, where each tick mark on an axis is a constant factor larger than the previous one.

$I_0$ (Reference Intensity): $I_0$ refers to the standard reference sound intensity, typically $10^{-12}$ W/m² in air.