Originally Posted by 7/11 The Crapshooter

What you are referring to is known as the Doppler Effect and it has some serious shortcomings in terms relative to the directional awareness of the specific sound and the frequency of that sound. Echo location is a science in and of itself however, having the ability to understand that echo in a manner that would allow the end user to actually locate the source based on the echo is now left to computers and a sensor array simply because of the difficulty. Don't believe this, roll your window down the next time you see a bike in your rear view mirror. As the bike approaches you can't here it until it is almost on top of you and this occurs even with the loudest of pipes. Flip it around and follow the bike and that sound can be heard at a very good distance.