Directivity Coefficient and Sound Attenuation

Sponsored Links

For a continuing sound source, the sound level in a room is the sum of direct and reverberant sound. The sound pressure for a receiver can be expressed as:

L_p = L_w + log( D / ( 4 π r² ) + 4 / R)          (1)

where

L_p = received sound pressure level (dB)

L_w = sound power level from source (dB)

D = directivity coefficient

R = room constant (m² Sabine)

π = 3.14

r = distance from source (m)

The figure below can be used to approximate the Directivity coefficient - D - for typical locations of the receiver and the sound source:

(1) can be transformed to express the difference between the received sound pressure and emitted sound power - the attenuation - as: 

L_p - L_w =  10 log( D / ( 4 π r² ) + 4 / R)          (2)

Combining (2) with the ratio between distance - r - from source and square of the directivity coefficient - D, and the rooms absorption - m² Sabine.

Sound Attenuation Calculator

The attenuation - (L_p - L_w) - can also be estimated from the diagram below:  

Sponsored Links

Related Topics

• Acoustics - Room acoustics, acoustic properties - decibel A, B and C - Noise Rating (NR) curves, sound transmission, sound pressure, sound intensity, attenuation and more ..
• Noise and Attenuation - Noise is usually defined as unwanted sound - noise, noise generation, silencers and attenuation in HVAC systems

Related Documents

• Abatement and Distance from Source - The disruption of sound pressures waves which reduces the noise is called attenuation - Sound Pressure Level Calculator
• Propagation of Sound Indoors - Sound and noise in a room will reach the receiver as direct and reverberant sound.
• Room Attenuation in Direct Sound Fields - Room size, absorption characteristics and attenuation in direct sound fields
• Sound Attenuation - Duct split to Terminals - Estimation of sound attenuation when ducts are split to terminals
• Sound Attenuation in Duct Elbows - Noise attenuation in a duct elbow is caused by reflected sound. It is only in larger ducts and at higher frequencies the attenuation is considerable
• Sound Power - Sound Power Level and the Sound Power from some common sources as fans, jet engines, cars, humans and more ..
• Sound Pressure - Sound Pressure is the force of sound on a surface area perpendicular to the direction of the sound