Types of Exhaust Resonators

Sound waves are energy-containing pressure waves created when a moving object quickly displaces the air around it. These pressure waves have certain physical dimensions, the most constant of which is frequency, or the distance between the strongest part of the pressure wave and the weakest part. Mufflers are tuned with channels and passages designed to capture, lect and dissipate certain wavelengths, but no standard muffler can capture all of them. Resonators are small mufflers designed to control frequencies the main muffler cannot.

Expansion Chamber

An expansion chamber is the simplest type of resonator and is essentially just a section of tubing that is much larger in diameter than the main tubing. The expansion chamber will capture any frequencies with a wavelength shorter than or equal to its length, causing them to bounce around inside the canister and cancel out. The expansion chamber is cheap and easy to produce but has a narrow range of frequency control.

Dissipative Muffler

A dissipative muffler starts out as an expansion chamber, but contains metal or fiberglass packing material that helps absorb the sound energy. The packing material is soft and pliable, allowing it to vibrate. This allows the sounds pressure energy to express on the packing material rather than the air, reducing its volume. Dissipative mufflers can use either a perforated core (a section of tubing in the center with many holes drilled through it) or a louvered core (a section of tubing with vents punched in it) to allow sound to enter the packing material while keeping the material where it belongs. Commonly called "glass-packs" or "cherry bombs," these high-flowing resonators are among the most common today.

Chambered Resonators

Also known as a Helmholz resonator, the "baffled" or "chambered" muffler uses a series of different sized cavities and chambers to catch sound waves and lect them back on themselves, thus canceling them out into an indistinct buzz. Helmholz resonators may utilize a single open chamber with several, angled metal plates (or "baffles"), a series of short, internal, perforated tubes, a separate expansion chamber containing packing material or any combination of the three. Helmholz resonators do an exceptional job of attenuating (canceling) the frequencies they are designed to target but may have little to no effect on frequencies outside their range. These resonators are designed to catch only the frequencies that the primary muffler cant and are generally tuned to work only with a specific engine/muffler combination. A chambered resonator may or may not produce the same exhaust note when used with a different engine or muffler.