Here is a brief, non-comprehensive, recent history of acoustic amplification (in images).  

We all understand intuitively that sound is physical, and that amplification and form are closely linked.  However, this relationship is often ill-considered or ignored in design that privileges optic effect.  Below are examples of projective sound geometries--some are highly visual, others must be experienced to be fully understood.  A future post will look at absroptive sound geometries.

No batteries included:

This 1970 installation by Michael Asher featured an entire gallery transformed into sound amplfying horn (courtesy: http://auralarchitectures.blogspot.com/).  The gallery door was removed for this exhibition, meaning that the space was available to the public around the clock.  Presumably, sound from the exterior could be amplified through this "double horn", and vice versa. 





a good resource to learn more about sound art:  
http://www.onelonelypixel.org/soundart.html