# Sound intensity level

Loudness measured in decibels (dB), a log scale where +10 dB means ten times the intensity.

Physics (university) · Part 05: Oscillations and waves · Card 11 of 11 · Last updated 2026-10-19

## Analogy

Earthquake scales also climb by powers of ten.

## Example

**Decibels**

dB = 10 log(I / I0)
I0 = 1e-12 W/m^2
dB = 10 log(1e6) = 60 dB

## In practice

An intensity of 1e-6 W/m squared is 60 dB.

## Practice

### Flashcards

- **How many dB is a tenfold rise in intensity?** 10 dB.

## Questions people ask

### Why do we use decibels?

Our ears respond to sound intensity on a roughly logarithmic scale. The range from a whisper to a jet engine is a factor of 10 to the 12. Decibels turn this huge range into numbers from 0 to about 120, which is easier to work with.

### How does intensity fall with distance?

For a small source spreading evenly, intensity equals power divided by 4 pi r squared. Doubling the distance cuts intensity to one quarter, which is about 6 dB quieter. This inverse square law is why a distant conversation sounds much softer than a nearby one.

## Related concepts

- [Simple harmonic motion](https://studyvisually.com/learn/science/physics-university/physics-university-part-5/physics-university-part-5-concept-1)
- [Period and frequency](https://studyvisually.com/learn/science/physics-university/physics-university-part-5/physics-university-part-5-concept-2)
- [Mass on a spring](https://studyvisually.com/learn/science/physics-university/physics-university-part-5/physics-university-part-5-concept-3)
- [Simple pendulum](https://studyvisually.com/learn/science/physics-university/physics-university-part-5/physics-university-part-5-concept-4)

Web page: https://studyvisually.com/learn/science/physics-university/physics-university-part-5/physics-university-part-5-concept-11
Study this card in the app: https://studyvisually.com/app/learn?category=physics-university&card=physics-university-part-5-concept-11