You need to look at the following links and get your head round the design aspects such as Helmholtz Resonators
Internal Muffler Design Aspects Helmholtz Resonators Alternatively .. once your totally confused and had enough... go to JP Exhausts and describe what you are trying to achieve. No doubt their engineers will have a particular approach and prefered design... and will inevitably produce something that will work.
At least the info above will enable you to understand what they are talking about. lol
