A motorcycle's exhaust muffler relies on a special device comprising a series of chambers or tubes to neutralise the roar of spent exhaust gases as they exit the motor. This device is called a baffle and is generally found in one of two forms: chambered baffles and absorption baffles. Many exhaust systems provided as original equipment for a modern motorcycle are designed with a chamber-style baffle. Aftermarket performance systems typically utilise an absorption-type baffle.
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A baffle's primary role is to reduce the intensity of the motorcycle's exhaust note, the sound waves generated by the combustion within the motor. Without a baffle in place, the exhaust note of a motorcycle can be dangerously loud and may even create legal problems if the machine is operated on the street.
A chambered baffle is composed of a series of compartments which the sound waves must pass through before exiting the muffler. As the sound waves move into the chamber, they are reflected back at the next set of sound waves, which effectively cancels out a small percentage of the sound before they move into the next chamber. This continues until the diminished sound waves exit the muffler.
An absorption baffle is constructed from an inner core of louvered or perforated steel tubing that extends down the length of the muffler. This inner core is wound within an insulated fibreglass mat called packing. As exhaust gases enter into the inner core, the sound waves pass through the louvres or perforations and are absorbed into the packing. The remaining sound waves exit through the mufflers outlet.
In addition to the perforated inner core found on most aftermarket mufflers, removable baffles are available to further reduce a motorcycle's exhaust note. The baffles are normally constructed from a short length of perforated steel tubing that is inserted into the muffler's outlet and secured by a small screw. Although they are not as effective at reducing the intensity of an exhaust note as the other forms of baffles, these smaller baffles have enjoyed some success in quieting the straight pipe exhaust systems that are frequently seen on cruiser motorcycles.
Pros and Cons
While baffles allow the average motorcyclist to ride through the city without causing alarm or garnering the attention of local law enforcement, they can rob the motorcycle of its performance capabilities. Due to their design, chamber-type baffles are much more restrictive, preventing the exhaust gases from exiting as smoothly and quickly as possible. Replacing the stock chambered muffler with an aftermarket absorption-style muffler straightens the exhaust flow, providing an increase in power. Maintaining an absorption-type muffler is also much simpler, since their design allows for regular replacement of the internal packing. Conversely, complete replacement is the only viable option for a damaged chambered muffler.
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