Believe it or not, your car muffler is as finely tuned as a musical instrument. No, it doesn’t make music like a musical instrument, it is tuned to eliminate the loud exhaust sounds that your engine makes. Let’s take a look at how this works:
First, let’s take a look at what “sound” really is. The phenomena of sound comes from pressure waves formed from pulses of alternating high and low air pressure. In an engine, these pulses are created when exhaust valves open and bursts of high-pressure gas pump into the exhaust system. The molecules of this gas collide with the lower-pressure molecules already in the exhaust pipe causing them to push on each other. In this way, the sound waves make their way down the pipe and when they eventually reach your ears, your eardrums vibrate back and forth which creates the sensation of “sound.”
Now comes the interesting part. As any physicist will tell you, it is possible to produce a sound wave that is exactly the opposite of another sound wave and if the two hit each other, they cancel out. Located inside a muffler is a set of tubes and baffles that are designed to do exactly this. A muffler is essentially a device to cancel engine sound waves.
However, when designing mufflers, engineers have to be careful to understand how much backpressure they produce in their designs. Because of all of the twists and turns the exhaust gas has to go through, mufflers like those just discussed produce a resistance to exhaust flow. According to David Stanley Chrysler of Midwest City, a local Chrysler, Dodge, Jeep, Ram dealer in Midwest City, OK, this can rob a little power of the engine which affects the vehicles gas mileage.
For those who modify their own cars, there are special types of mufflers that are designed to reduce backpressure. One type, sometimes called a “glass pack muffler,” uses only absorption techniques to reduce the sound. On a muffler like this, the exhaust goes straight through a pipe that is perforated with holes. No wave cancellation is involved.
To enjoy the best of both worlds – easy flowing yet quiet mufflers- several car manufacturers have been experimenting with active noise-canceling mufflers. These systems incorporate electronic components that measure the exhaust sound level and generate counter-balancing sound waves to quiet the exhaust sound. These are being used on some large industrial engines but not yet on cars, at least not just yet. In the constant search for increased efficiency and mileage, we may be seeing this type of muffler in the future.