US Patent 8256571 Frequency-modifying muffler

A muffler for raising the audible pitch of an internal combustion engine's exhaust note that includes an enclosed case having an inlet and an outlet, and a plurality of flow-directing components which are adapted to subdivide an inlet flow into a plurality of interior flows, including a first interior flow providing the shortest flow length through the muffler between the inlet and the outlet, a second interior flow having a flow length at least about twice the length of the first interior flow, and one or more intermediate flows following by-pass passages to split off from the second interior flow between the inlet and the outlet and having flow lengths between the flow lengths of the first and second flows.