Physics: Waves: Soprano and a bass start singing at the same time, from equally far away. Who is heard first

Suppose a soprano and a bass start singing at the same time, from equally far away. whom will you hear first? Why?

Sound travels at a constant speed through a vacuum, isn't that correct? My intuition would be that, if in a vacuum, I would hear them at the same time.

In other media, I'm not too sure. Would it change? I know that light waves depend on wavelength (which affects refractive index). Is it the same with sound waves?

You hear the the singers at the same time. The speed of sound in air is the same whatever the frequency (or wavelength) is.

Sound can't travel through a vacuum as sound waves need material to vibrate. You are probably confusing sound with light which can travel through a vacuum. See link.

(Light behaves differently to sound and the speed of light in materials varies slightly with wavelength. E.g. blue light is slightly slower in glass than red light, In a vacuum all colours of light travel at the same speed.)

The word you're looking for is "dispersion". That's the name for the dependence of sound velocity on wavelength or frequency.

Most mediums are actually dispersive. As you point out, transparent materials are dispersive for light. The ocean is dispersive for water waves, with low frequencies traveling faster.

I was surprised when I learned that air is non-dispersive for sound waves but actually I think that's only an approximation. A little googling turned up this article on sound dispersion in gases:
http://www.nature.com/nature/journal/v13…
Apparently there's dispersion in some conditions but not in others.

sound waves for their propagation requires medium (mechanical waves) so in vacuum you will not hear any kind of sound.in any other medium it depends on the conditions(loudness, pitch).