Relation between cavity resonance and sound speed

[haleycomet2]

Our sound will be like "Donald Duck" if we inhale helium gas and the explanation from web is because" The cavity resonances which determine the vocal formats would be raised by the higher sound speed,"(http://hyperphysics.phy-astr.gsu.edu/hbase/sound/souspe.html). Why cavity resonance raise as sound speed raise?

 

[tiny-tim]

hi haleycomet2!

wavelength depends only on cavity size

frequency depends on … ? ​

 

[haleycomet2]

hi haleycomet2!

wavelength depends only on cavity size

frequency depends on … ? ​

If wavelength depend only on cavity size,then the frequency of sound is higher as the speed of gas becomes higher(cavity size stay constant when we make comparison of two gases ).

However, some says that the frequency is only depend on vocal folds and it is independent of the gas.And the only change is the timbre.

Both explanation looked convincing but i don't know which is true.

Besides,why the cavity resonance is raised when sound speed get higher(cavity size remains same)?