Originally Posted by nismodreamr

HKS Hi Power. the resonator design fits exactly what you described wanting, quiet in low rpm but comes alive at WOT, the design allows lower speed of exhaust gas (lower rpm) to utilize the second canister on top of the muffler and keeps sound down, but when you have higher exhaust gas speeds (higher rpm) the canister on top of the muffler is bypassed and the volume is obviously increased.