"Bob Cain" wrote in message

Arny Krueger wrote:


I do believe it is in Halliday and Resnick, even though it has been
decades since I read it there.

It's also in the JAES papers that have now been cited several times
in the various discussions on the various newsgroups.

Since you have those papers, Arny, is there any chance that
you could locate the expression and post it?

Here's one of many which together include various presumptions about
radiation pattern, etc.

AES preprint 1844, October 1981

Authors: Allison and Villchur

DFT = 0.019 Al f2

DFT = FM distortion factor (the square root of the ratio of power in the
sidebands to the total power of the f2 signal and sidebands, expressed as a
percent or total radiated power, presuming the speaker is a hemispherical
radiator.

A1 = center-to-peak cone excursion at the modulating frequency (in inches),

f2 = FM modulated frequency,