Seriously, there is more than decibel level, there is also pitch and tone. People in the car world seem oblivious to pitch and tone, no matter what kind of car we are talking about.
I don't put a glasspack on my Jeep because a straight six with a 'pack sounds goofy. A small cube motor with not reverb or expansion chamber in the exhaust outlet will sound like an old farm truck. Which some people think sounds just awesome, "the sound of performance" whatever floats your boat in the end, but if you want a truly good sounding, not just hillbilly approved car, you gotta pony up for a good catback, of a flow through variety.