I've been looking for info on the correlation between barrel length and sound db levels in 9mm suppressed but not having much luck.

Host gun will be a Sig MPX with an Octane 45HD running subs, mostly 147's. It has an 8" barrel but looking to chop and re-thread. Ideally, I'd like a length around 4.5", but would go longer if there will be a noticeable sound reduction on say a 6.5" barrel. So the question is what length to go with.


Traditionally the shorter the barrel, the more pressure and louder the shot. However, FPS will increase with barrel length and possibly increase flight noise. I don't imagine I would be pushing super sonic with 147's anyway. Is there a sweet spot or will I even hear much of a difference between a 4.5" and 8" barrel?