Effect of Humidity and Density on Speed of sound

[FysicsPhorums]

Hi, I've been trying to look up the effects of density and humidity on the speed of sound, and I've been finding conflicting results. Some websites have stated that increased humidity will increase the speed of sound because of decreased density in the air, but wikipedia's speed of sound article states that the speed of sound "is nearly independent of pressure or density for a given gas".

Also, I'm familiar with the example that sound propagates faster through iron than in air, but is this due to stronger intermolecular interactions or the greater density of the material (or both)?

Can someone help clarify how humidity and density affect the speed of sound? Thanks

 

[Gordianus]

The speed of sound c is given by:

c=sqrt(\gamma R T/M)
where \gamma is the ratio of specific heats, R the gas constant, T the temperature and M the molar mass.
Both \gamma and M change with humidity but the change is so small I wouldn't bother in a "standard" situation.