Subject: Sound Waves; and their reactions within an environment

I've been interested in car audio for several years, and there has 
always been a term I've been puzzled by.  In the car audio industry
they will sometimes refer to a car's 'transfer function'; (the cars
ability to enhance the sound passively).  I understand that each 
frequency of sound has a different length; this length may or may not 
fit within the distance of the car. (ie: front to back, side to side). 
How does a person calculate, then use the car's 'transfer function' to
enhance the listening environment?

Re: Sound Waves; and their reactions within an environment