Function and Necessity of Exhaust System's Resonator

Workers inspecting an exhaust system

Joe Raedle / Getty Images

In car circles, you hear a lot of people talking about resonators. Is it a muffler? Is it part of a stereo system? What exactly is a resonator? The resonator is part of your exhaust system, but it is not the muffler. It is sometimes known as a pre-muffler because it is installed in the exhaust system after the catalytic converter and before the muffler. Some cars and trucks have them, others don’t. 

When to Replace a Bad Resonator, or Skip It

There are two situations that would call for you to replace or install a resonator. The first is when your car was equipped with a resonator from the factory. This is described in detail below. The second situation would be if you were adding a custom exhaust system to your car or truck. Custom systems are tuned more for horsepower than for quietness, but adding a resonator keeps things down to a dull roar while still freeing up the exhaust for the engine to make maximum power. Resonators are often used in custom exhaust systems to give them that deep, throaty sound that so many performance cars have, and want! If your resonator has rusted out, or you're repairing your exhaust system and wondering if it's worth the extra few bucks to replace the resonator, it is. Skipping it can really screw up the way your engine is tuned. 

Function of a Resonator

A resonator installed as part of your car or truck’s exhaust system serves one main purpose — to resonate. It’s sort of an echo chamber for your car’s exhaust, preparing all of the loud noise coming from your engine for the muffler to silence it. But there is far more science to it than that. The resonator doesn’t just remove sound, it changes it. When your car was designed, there was a team of acoustic engineers working to be sure any sounds that come from your vehicle while you’re driving are as pleasant as possible. Obviously, the most pleasant drive for many people would be a silent car! The problem these acoustic engineers run into is the quieter you make an engine, the less powerful and efficient it becomes. You could design a muffler that would make almost no noise come out of the car’s tailpipe, but it would be so restrictive that your car would be hideously slow and get terrible gas mileage! Like so many things in life, and in cars, the answer is a compromise. The muffler quiets just enough noise to make things pleasant without missing the point of having a car or truck in the first place. As exhaust systems developed, engineers realized that you can play with the sound before it reaches the muffler and squeezes some more efficiency and power from the engine without making it any louder. This answer was the resonator. Exhaust pulses entering the exhaust system at the engine are filled with high and low-frequency sounds. The sounds bounce back and forth inside the pipe, changing a little bit as they go, especially when they change direction inside the pipe. The engineers realized this and decided to look for a way they could take advantage of it. They learned that if they designed an empty chamber for the exhaust to travel through, the pulses would bounce around in there — resonate — and some of them would cancel each other out. As luck would have it, the annoying higher tones were more likely to be canceled out. This made the job of the muffler much easier without robbing any efficiency or power from the engine. Resonators have continued to develop over the years, and now most cars take advantage of the technology.