Isolation Room Design Calculator

Source Sound Power. It adds directly to the result decibel-for-decibel (SPL at Receiver = Source Sound Power minus Total Path Loss), while Distance, Frequency, Ground Type, Temperature, and Humidity only reshape how much loss gets subtracted -- none of them move the result as directly or as much as the source power itself.

A point source's sound energy spreads spherically in all directions, so its geometric loss follows a steeper 20 x log10(distance) relationship. A line source (like a highway) spreads cylindrically, following a shallower 10 x log10(distance) relationship, because the source is continuously distributed along a line rather than concentrated at a point -- which is why traffic noise doesn't drop off as quickly with distance as a single machine does.

Hard, reflective ground (concrete, water) reflects sound coherently back toward the propagation path rather than absorbing it, which this calculator models as roughly 3 dB less total attenuation than a purely free-field prediction. Soft ground (grass, soil) does the opposite -- it absorbs additional sound energy, adding up to 10 dB of extra attenuation that grows with distance.

It matters most at high frequencies and long distances -- at this calculator's 500 Hz default, atmospheric absorption is a small contributor to Total Path Loss compared to geometric spreading. Raise Frequency toward the ultrasonic range or extend Distance and atmospheric absorption's share of the total grows substantially, since the underlying ISO 9613-1 molecular relaxation model is strongly frequency-dependent.

Atmospheric absorption comes from molecular relaxation of oxygen and nitrogen in the air, and both relaxation frequencies depend on humidity, while the overall absorption coefficient also depends on temperature. Neither input alone determines the absorption coefficient -- the ISO 9613-1 model this calculator implements requires both together.