Thanks guys. I am frankly amazed it is working so well. The 350Z setups are actually different, but work on the same principle. This is the whole argument between AWE and APR that showed up in another thread, where the there was a pretty fare amount of flame going back and forth about sound cancellation theory. Basically this is not a Helmholtz chamber, though it could be working as one in addition to its real intended purpose. The difference is in how the cancelation wave is generated. I will skip all the vague arguments about which is better or who has a bigger shop and just jump to the end.
1. In a Helmholtz chamber the air in the throat of the chamber is oscillating back and forth because of the spring action within the chamber (the 350Z idea above, and what is used in AWE/Magnaflow/etc exhausts). If this is at 1/4 or 1/2 (or some 1/4 or 1/2 multiple), the two pressure waves eat each other's lunch and we are happy. Here, the sound in the exhaust is not needed as a driving function, the velocity of the gasses travelling across the connection produce the oscillation, and the volume of the chamber and the relative geometry of the connecting throat are the critical items to get it to produce the correct cancelation pressure wave.
2. In a reactive silencer, the standing wave produced by the driving function in the exhaust tone is sitting pretty within a length of side passage. The distance travelled from the entrance to the end cap length of the chamber is 1/4 that of the driving wave, and again they eat lunch and we are happy. What I designed and built was a quarter wave length reactive silencer similar to what APR has licensed from CORSA, and is part of the famed NASA reference that shows up in forum posts regularly.
Everyone (including myself when I started this thread) keeps describing reactive silencers and Helmholtz chambers the same thing. They are not. But here is the catch, they both require to be tuned to specific frequencies (neither are broad band regardless of what any vendor tries to sell you), both both do the same thing, both suffer from changes in the temperature of the chamber, and both can do their job just as well.
Now here is the part that fuels all the arguments, the Helmholtz chamber is potentially more sensitive to pressure and temperature fluctuations than the reactive silencer. So even though a correctly designed Helmholtz chamber will work 100% as well as a reactive silencer, it:
1. Suffers from changes in the environment easier and won't work as well over as many conditions. Basically it is a touchy biatch and if it ain't happy, it don't go shopping. You could fix this by ensuring that the chamber temperature is always spot on in all times of the year, and tune it right, but it is just damn touchy.
2. THIS IS IN MY OPINION THE BIG ONE - It doesn't need a driving function. In other words, it will produce the blowing across the beer bottle sound even if there is no sound to cancel, in which case it is ADDING TO THE EXHAUST NOISE in the absence of drone. Basically it becomes the drone when its evil twin is not around for it to have lunch with. Don't know if this is the cause of the reactive silencer being better or not, but it is my speculation that it is part of it.
Happy holidays, and I am excited to see if the vendors chime in her and correct me or start biatch slapping each other again. :-) Come on, it is Sunday, I don't attend church and we need entertainment.