Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!

This is an AMP page - Open full page! for all features.

• the most efficient way to navigate the Engineering ToolBox!

# Propagation of Sound Indoors - the Room Constant

## In a room the sound or noise will reach the receiver as direct and reverberant sound.

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

Lp = LN + 10 log (D / (4 π r2) + 4 / R)                                 (1)

where

Lp = received sound pressure level (dB)

LN = sound power level from source (dB)

D = directivity coefficient (typical 1 for receivers in the middle of the room)

R = room constant (m2 Sabin)

π = 3.14....

r = distance from source (m)

### Room Constant

The room constant express the acoustic property of a room.

R = A / (1- αm)

= Σ Si αi / (1- αm)                                    (2)

where

R = room constant (m2 Sabine)

A = total room sound absorption (m2 Sabine)

αm = mean absorption coefficient of the room

Si = individual surface area in the room (m2)

αi = absorption coefficient for individual surface in the room

The sound power generated from a machine is 90 dB. The machine is located in a room with total sound aborption 12.2 m2 Sabine and mean absorption coefficient 0.2.

The room constant can be calculated as

R = (12.2 m2) / (1 - 0.2)

= 15.3 m2 Sabine

For a receiver located in the middle of the room with a directivity coefficient 1 and distance 2 m from the source - the received sound pressure level can calculated as

Lp = (90 dB) + 10 log (1 / (4 π (2 m)2) + 4 / (15.3 m2 Sabine))

= 84.8 dB

## Related Topics

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

## Search Engineering ToolBox

• the most efficient way to navigate the Engineering ToolBox!

## SketchUp Extension - Online 3D modeling!

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with the amazing, fun and free SketchUp Make and SketchUp Pro . Add the Engineering ToolBox extension to your SketchUp from the Sketchup Extension Warehouse!

## Privacy

We don't collect information from our users. Only emails and answers are saved in our archive. Cookies are only used in the browser to improve user experience.

Some of our calculators and applications let you save application data to your local computer. These applications will - due to browser restrictions - send data between your browser and our server. We don't save this data.

Temperature

oC
oF

Length

m
km
in
ft
yards
miles
naut miles

Area

m2
km2
in2
ft2
miles2
acres

Volume

m3
liters
in3
ft3
us gal

Weight

kgf
N
lbf

Velocity

m/s
km/h
ft/min
ft/s
mph
knots

Pressure

Pa (N/m2)
bar
mm H2O
kg/cm2
psi
inches H2O

Flow

m3/s
m3/h
US gpm
cfm

3 10