Spectrum of FM signal?
Because frequency modulation is a nonlinear phenomenon, there's no good general-purpose answer to your question.  You can take any specific baseband signal and figure out its modulated spectrum, but that's it.
For lack of a better technical term, FM modulation takes the frequencies in the parent signal and munges them together, spreading them out by more than the deviation frequency.  For a sine wave this is that Bessel function.  For a pair of sine waves, it'd be all the harmonics of each sine wave plus all possible combinations of intermodulation ($n f_1 + m f_2\, \forall\, n, m \in \mathbb{Z}$) -- so for the two-sine case there may be some discernible, identifiable lines in the output.  For sound with a continuous spectrum, you'll get a continuous spectrum out, but nothing you could just recognize on a spectrum analyzer.
For practical purposes, you're left with rules of thumb, inspired by the above results but limited by our inability to solve the nonlinear differential equations in any general way.  If you have a signal with bandwidth $B$, and a maximum frequency deviation of $f_D$, then the bandwidth of the transmitted signal can be limited to $2(B + f_D)$.  This isn't satisfying from a theoretical standpoint, but it's backed by over 70 years of practical experience with broadcast and voice communications systems.