This tool takes the **sound pressure level** (SPL) measured at a known distance **d _{1}** from the source and uses it to calculate the attenuation and SPL at another distance

**d**away. The term sound can be replaced by

_{2}**noise**as this will also calculate noise attenuation with distance.

Enter the following: **SPL _{1}, d_{1} **and

**d**

_{2}**Formula**

**SPL _{2} = SPL_{1}−20*Log_{10}(d_{1}/d_{2})**

**Background**

Decibels, or dB, are a unit used to measure sound pressure levels. The closer the listener is to the source, the higher the SPL.

SPL decreases exponentially with increasing distance.

**Example Calculation**

A speaker specifications will typically tell you what the SPL is at 1 meter. A typical number is **SPL = 85 dB** (1W/1m).

Use this calculator to find the SPL at the edges of the space that you want to cover.

For instance, with the above speaker if the furthest distance from the speaker in a large room is 20 meters, the SPL at that point is calculated to be 59 dB. The total attenuation is 26 dB.

**Related Calculators**

- Amplifier Speaker Matching – In the example above we found the SPL at 20m. Use this tool to find the amplifier gain (Watt) required to boost that by any number of deciBels.
- Max SPL Calculator – explore the limits of your equipment
- Add Sound Pressure Levels – this tool makes it easy
- Sound Pressure Level – if an amplifier is used with the speaker, what is the SPL at a specified distance away from the speaker?