Not running any tubing past the muffler results in the exhaust bouncing off the road and car. This is what causes that deep rumble. Some people run dumps in front of the axle, pointed down at the road, to heighten this effect. I myself don't care for it. Mostly because 20 years of loud cars, loud music, loud bikes, wind noise, etc. has left me with a nice ringing in my right ear, and some hearing loss too. 
Each to his own, though. In 20 years or so, they'll understand.
Each to his own, though. In 20 years or so, they'll understand. 
