AcouVApp Field

How to Calculate Diffuse and Direct Sound Levels from Acoustic Power

This calculation helps estimate the diffuse and direct sound levels from the acoustic power level of a source. It is crucial in determining the overall noise environment of a room or space.

Formula for Calculating Total Sound Pressure Level (L_ptotal):

• R is called the room constant and is calculated using the formula: \[ R = \frac{S \times \alpha_{mean}}{1 - \alpha_{mean}} \]

Conditions Indicating a Non-Diffuse Field:

This calculation is valid in a diffuse field condition, where sound is evenly distributed. It does not account for the modal aspect of the room, which is a factor at frequencies below the Schroeder frequency.

A sound field is considered non-diffuse when one or more of the following conditions are met:

• Uneven distribution of sound absorption on surfaces, such as when only one surface is highly absorbing
• Lack of sound diffusing or scattering elements, like furniture, in the room
• Room dimensions where the ratio of longest to shortest room dimensions is higher than three
• Very large volumes, typically over 5000m³

Schroeder Frequency Calculation

The Schroeder Frequency (f_s) is calculated using the formula:

\[ f_{s} = 2000 \times \sqrt{\frac{T}{V}} \]

Where:

• T is the reverberation time (mean across all frequency ranges)
• V is the volume of the space

The critical distance in room acoustic

The distance from the source, where the contributions from the direct field and the diffuse field are equal, is called the critical distance (sometimes hall radius or also room radius for the case where the directivity factor is equal to 1.0).

The formula is :

\[r_c = \sqrt{\frac{QR}{16\pi}}\]

For further reading, see: Engineering Noise Control - Theory and Practice - Bies.

Learn more about room modes or explore our acoustic product database.