The law does not tie the sound level to the mechanical device. See the Kansas law attached below. It is in new Section 7.

i had a run in last year with a wayne county sheriff....He told me my boat was to loud, i asked him if he had a decibal reader he said no but he knows for sure mine is to loud...........End result no ticket but he told me i need mufflers...........Around me they like the hoarspower as much as we due, just dont run around at midnight at wot...........Most cops are not looking to give ya a hassle unless your duing something stupid.....