Strutt|Building Acoustics|Sound Level in Small Rooms (Schultz) calculates the total sound level in a small highly-absorptive room (e.g. a private office or domestic room) using the following formula:
`L_p=L_w-10log(r)-5log(V)-3log(f)+12`
where:
`r` is distance from source (m)
`V` is room volume (m³)
`f` is frequency (Hz)
Reference: Ver and Beranek Noise and Vibration Control Engineering, 2nd Edition, Section 7.4