Formula:
f _c = [ sqrt(3)c²/pi*d ] * [ sqrt(ρ/Y) ]
where,
f_c = Coincidence Frequency [Hz]
c = Speed of sound in air [ms^-1]
d = Thickness of panel [m]
ρ = Density of panel [kgm^-3]
Y = Young\'s modulus of panel [Nm^-2]