Have a look on youtube. I have just bough the Afterburner Vortex which is meant to be louder than the Ninja and I think the Vortex is just right TBH. I had a PPP backbox previously and that was almost too quiet!!

 

Hi. I have just replaced my prodrive with a ninja II backbox, it got a nice sound not to loud and i get no drone when driving.

Stuart.

 

i've heard a ninja backbox, imo they sound really good. nice rumble plus not ott loud

wiley