Sound pressure level

Professional Definition

The magnitude defined by the formula: L = 20 log(p / p0) [dB], where p is the effective value of the sound pressure, and p0 is the reference pressure (usually 20 µPa).

The sound pressure level (English: Sound Pressure Level – SPL) is the logarithmic ratio of the measured sound wave pressure to the threshold of human hearing. This value is expressed in decibels (dB). It is important to remember that this is a scalar quantity, depending on the measurement location and the distance from the source, in contrast to sound power, which is a characteristic of the source itself.

Acoustics in Simple Words

Imagine trying to measure the height of buildings, but in your city, there are both LEGO block houses (whisper pressure) and skyscrapers reaching the Moon (rocket launch pressure). Using a ruler would be impossible due to the number of zeros in the result. That is why we use clever mathematical "compression" – the decibel scale. The sound pressure level simply tells us, how strongly the air is "pushing" on our ears at any given moment, but expresses that in convenient numbers from 0 (absolute silence) to around 140 (physical pain).

Summary

The sound pressure level is the most commonly encountered parameter defining "loudness" at a given point. This is the value indicated by sound level meters and smartphone applications measuring noise. It is crucial in designing acoustic insulation and in occupational safety regulations concerning hearing protection.