# Transmission loss

Sound measurements
Characteristic
Symbols
Sound pressure p, SPL,LPA
Particle velocity v, SVL
Particle displacement δ
Sound intensity I, SIL
Sound power P, SWL, LWA
Sound energy W
Sound energy density w
Sound exposure E, SEL
Acoustic impedance Z
Speed of sound c
Audio frequency AF
Transmission loss TL

Transmission loss (TL) in general describes the accumulated decrease in intensity of a waveform energy as a wave propagates outwards from a source, or as it propagates through a certain area or through a certain type of structure.

It is a terminology frequently used in optics and acoustics. Measures of TL are very important in the industry of acoustic devices such as mufflers and sonars.

## Definition

Measurement of transmission loss can be in terms of decibels.

Mathematically, transmission loss is measured in dB scale and in general it can be defined using the following formula:

TL = ${\displaystyle 10\log _{10}\left\vert {W_{i} \over W_{t}}\right\vert }$ dB

where:

• ${\displaystyle W_{i}}$ is the power of incident wave coming towards a defined area (or structure);
• ${\displaystyle W_{t}}$ is the power of transmitted wave going away from the defined area (or structure).

## Applications

Transmission loss may refer to a more specific concept in one of the field below.

## References

1. ^ ISO 18405:2017 Underwater acoustics - Terminology (International Organization for Standardization, Geneva, 2017)