inverse square law ?

[Randall_Oelerich]

If you cut the distance from the mic to the actor in half, I thought that the signal picked up by the mic quadruples, not just doubles. Am I wrong?

I started watching the DVD Sound for Film and Television by Barry Green and David Jimerson with Matt Gettemeir, and in their DVD section on the inverse square law they say that cutting distance in half doubles the sound picked up by the actor--which to me seems to ignore the key word "square" in the inverse square law, where intensity of the sound (or light) is proportional to the inverse of the square of the distance. Intensity = 1/(d*d), so if new distance is 1/2 original distance, the new intensity should be
new intensity of sound = 1/[(1/2)(1/2)] = 1/(1/4) = 4, viz quadrupling not just a doubling.
~randall

 

[Barry_Green]

Quadruples the power, but doubles the VOLUME. Not the same. We were keeping it simple by pointing out that the perceived volume will drop by 6dB with doubling the distance.

 

[Randall_Oelerich]

Thank you Barry for clarifiying. Okay that makes sense somewhat; i just did some more googling and discovered some nice information on this that supports what you say, helps me (and hopefully others here) understand this better--

Loudness is not the same as intensity:
http://hyperphysics.phy-astr.gsu.edu/hbase/sound/loud.html#c1

Sound Intensity:
http://hyperphysics.phy-astr.gsu.edu/hbase/sound/intens.html#c1

Inverse square law and sound:
http://hyperphysics.phy-astr.gsu.edu/hbase/Acoustic/invsqs.html

Quadruples the power, but doubles the VOLUME. Not the same. We were keeping it simple by pointing out that the perceived volume will drop by 6dB with doubling the distance.