Do they make a difference in the sound of the exhaust?

For example i have a HKS Super Drager exhaust which i dont class as particularly loud (resonated centre also) would fitting a decat downpipe make it any louder?

 

Yes,take out the resonated centre section if you want even louder (pissing off the neighbours louder )

 

Excellent, as its a nice looking box to be honest, but lacks the scooby rumble unless im on full chat lol