This calculation will give you the amount of attenuation, in decibels, you can expect with a change in receiver distance, in a free field (outdoors). For example if you were standing 10 feet from a noise source, and were to move 100 feet away from that noise source, you would expect to see a drop in level of 20dB. Sound that is radiated from a point source drops in level at 6dB per doubling of distance. If you start at 50 feet from the source and move to 100 feet from the source you will have a 6dB drop in level. If you move from 500 feet to 1000 feet, you will have a 6dB drop in level. For the record, the formula to calculate this level drop is: Decibels of Change=20xlog(distance 1/distance 2), and you can calculate it on any scientific calculator.
This information is provided with no warranty of its accuracy, or applicability, and any use made of this information is done so at the sole risk of the user.
Mc Squared System Design Group, Inc
323 - 901 West 3rd Street
North Vancouver, BC V7P 3P9
Phone 604 - 986 - 8181