Transmission loss

Sound measurements
Characteristic	Symbols
Sound pressure	p, SPL
Particle velocity	v, SVL
Particle displacement	δ
Sound intensity	I, SIL
Sound power	P, SWL
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

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:

$TL = 10 \log_{10} \left\vert {W_i \over W_t}\right\vert$

where:

• $W_i$ is the power of incident wave coming towards a defined area (or structure);
• $W_t$ 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.

Duct Acoustics

• Transmission Loss (duct acoustics) in duct acoustics describes the acoustic performances of a muffler like system.

Room Acoustics

• Transmission Loss in room acoustics describes the decrease of sound intensity that is reduced by a wall or other structure at a given frequency.

Underwater Acoustics

• Propagation loss (sometimes referred to as transmission loss) is a quantitative measure of the reduction in sound intensity between two points, normally the sound source and a distant receiver.

References