Transmission loss

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Sound measurements
 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.


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 = dB


  • is the power of incident wave coming towards a defined area (or structure);
  • is the power of transmitted wave going away from the defined area (or structure).


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

Electrical engineering[edit]

Duct Acoustics[edit]

Room Acoustics[edit]

Underwater Acoustics[edit]


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