Just adding in some info here:
Inline straight through resonators are similar to glass packs in design. Inline resonators will not restrict flow, where as the glass packs will (only sightly). The difference is in the inside pipe, louvers in glass packs vs perforated holes in resonators. Resonators typically will only quiet exhaust down a little roughly 2-3dbA per foot, especially with mine because I have a lot of resonator length. Glass packs act more as a straight through muffler and typically absorb more sound leaving a unique note. Both absorb sound waves via steel wool/fiberglass and resonating chamber, altering the exiting sound waves and minimizing drone.
I measured my inline resonators: I have stock exhaust manifold and a high flow cat with 2.25" piping from the cat back. Large resonator is 3 feet and the small one is 1 foot. So obviously a total, 4 feet of resonator length. Which is why mine is so quiet.
Example: Resonator (left) Glasspack (right)
Helmholtz or side branch resonators are tuned to a certain frequency (using a formula like Phil1542 in the first post). The sound waves are interrupted/canceled from the resonator back and typically work best when installed closest to the engine as possible. This design will typically not lower the volume or loudness of the exhaust but interrupt the sound waves changing the frequency. This is achieved by using a separate sealed chamber or pipe as you have seen in earlier posts.
Example
Just posting what info I have found.
Please correct me if I'm off on anything. This is how I understand it.
. Maybe I'll weld in one of those electric open exhaust valves to play around with and put it right at the Y split, haha.
