Does the size of an animal's ear effect how good it's hearing will be?

A lot of it has to do with the shape of the actual ear itself (as in dogs, which can control their ears with muscles to maximise hearing depending on the circumstances).

Dolphins have a huge hearing range (1-150kHz) and yet have no obvious big flappy ears!

 

Desert animals often have large ears to lose heat (greater surface area with veins close to the surface).

Desert animals often have large ears to lose heat (greater surface area with veins close to the surface).

 

...and along those lines, Allen’s Rule states that within the same species of warm-blooded animals, individuals from populations living in colder environments tend to have shorter appendages (limbs, ears, tail, etc) than do those from populations in warmer areas because of the selective advantage it provides. Short arms, legs, and other appendages have relatively less skin surface area and radiate less heat into the surrounding environment. In the warmer environments, longer appendages provide greater surface area and can radiate more heat so that the animal does not overheat. Thus, smaller appendages retain more heat and larger appendages radiate more heat. Allen’s Rule is a corollary of Bergmann’s Rule.