Mufflers and how they work


If you have ever heard a car running without a muffler, the purpose of a muffler becomes all too clear. Mufflers are all about noise, or rather the lack thereof, from the car itself.

Sound: Sound is formed when alternating pulses of high and low pressure create a pressure wave. This wave makes its way into the air (creating-sound.) When these pressure waves hit your eardrum, the eardrum vibrates. Your brain interprets this as “sound.”

In an engine, the pulses are created when a burst of high pressure gas is released by the opening of the exhaust valve. The molecules in the high pressure gas hit the lower pressure molecules that are already in the pipe. This creates a stacking of the molecules. This stacking continues down the pipe which leaves the low pressure behind. In other words, the sound makes its way down the pipe faster than the gasses do.

Affects of sound: When sound waves hit your ear, there can be different types of waves that hit at the same time. Since it IS possible to create a wave that is the direct opposite of another wave, you can cancel out “sound.”

There is a chamber inside the muffler called the resonator. Contained in the resonator is a volume of air which has a length calculated to produce a wave which cancels out a frequency of the sound created by the car gasses. Were you to look inside a muffler and “see” the sound waves, you would see some traveling in one direction, and some traveling in the other direction, indicating the high pressure and the low pressure. Where the high and low pressures align, they cancel each other out, thus “cancelling” the noise. In some higher end cars, there is an extra resonator outside of the muffler that further reduces engine noise coming from the exhaust.

There are newer type mufflers which reduce the amount of back pressure caused. Back pressure can increase engine strain. While they do decrease the back pressure, they do not muffle sounds as well. Even newer studies are concentrating on using microphones and a speaker. These studies are done on things like generators to see how much noise can be reduced.

So now that you see how much actually goes on inside a muffler, it’s easy to see how they can wear out. There is a lot going on inside those simple looking car appendages! Can you imagine the level of noise if no one had mufflers? It’s almost deafening when we come across one car without one! Understanding the workings of a muffler make the price seems a little more reasonable too. They are creating a sort of peace between man and machine to help them co exist in a world which already has enough headache inducing products.

It is normally pretty easy to tell if the muffler is having problems. What is not easy to see, however, is if it is the muffler itself, or a pipe connecting the muffler in some way. The pipes can sometimes be more of a cost than the muffler.

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