People use this horn-shaped speakers not for aesthetic purposes. As a matter of fact, this shape is able to amplify the sound. Now, taking into account that sound is energy and that no energy other than the sound input is fed to this speaker, the previous statement definitely violates the rules of thermodynamics, because amplifying energy with no other energy input is.. not possible.
On the other hand, our ears definitely tell us that this thing actually works! But how?
Well, it has to do with matching impedance. If you've worked with transistor or other amplifier circuits, you definitely know what I'm talking about. Watch the following video to get the idea.