A more detailed approach for sound pressure/power conversion based on room acoustics considerations is given in the Calculation of Room Correction for Surface Properties spreadsheet 
(98 KB).
This spreadsheet calculator is based on a commonly accepted room acoustics method that computes the relationship between the source sound power level and the reverberant field sound pressure level. The spreadsheet assumes a greater degree of sophistication on the users’ part, and requires that measured data be available in octave bands.
Two scenarios are covered by the spreadsheet:
- Estimate installed Sound Pressure Level from measured Sound Power Level
- Estimate Sound Power Level from measured Sound Pressure Level
The spreadsheet may also be used to estimate installed sound pressure level from sound pressure level measured in a different environment sing the following steps:
- Enter the volume, surface areas and types for the room in which the measurement was performed
- Enter the measured octave band sound pressure levels in Row 45.
- Copy the estimated sound power levels from Row 46 and paste them into the input cells in Row 40.
- Now edit the volume, surface areas and types to correspond to the room in which the equipment will be installed.
- Read the estimated sound pressure levels in Row 41.
Note: Sound absorption coefficients are from commonly accepted sources and are adapted with permission from Noise Control for Buildings and Manufacturing Plants, by Hoover and Keith Inc., Houston, TX, USA.