If you've ever heard a car engine running without a muffler, you know the difference it makes to the noise level coming from your vehicle's exhaust system. The muffler is designed to reflect the sound waves produced by the engine in such a way that they partially cancel themselves out.
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Where Does the Sound Come From?
Sound is a pressure wave formed from pulses of alternating high and low air pressure. These pulses make their way through the air at -- you guessed it – the speed of sound.
In an engine, pulses are created when an exhaust valve opens and a burst of high-pressure gas suddenly enters the exhaust system. The molecules in this gas collide with the lower-pressure molecules in the pipe, causing them to stack up on each other. They in turn stack up on the molecules a little further down the pipe, leaving an area of low pressure behind. In this way, the sound wave makes its way down the pipe much faster than the actual gases do.
How does a Muffler cancel out sound?
Located inside the muffler, you'll find a deceptively simple set of tubes with some holes in them. These tubes and chambers are actually as finely tuned as a musical instrument. These tubes are designed to create reflected waves that interfere with each other or cancel each other out. The exhaust gases and the sound waves enter through the center tube. They bounce off the back wall of the muffler and are reflected through a hole into the main body of the muffler. They pass through a set of holes into another chamber, where they turn and go out the last pipe and leave the muffler.
Typically, the body of the muffler is constructed in three layers: Two thin layers of metal with a thicker, slightly insulated layer between them. This allows the body of the muffler to absorb some of the pressure pulses. Also, the inlet and outlet pipes going into the main chamber are perforated with holes. This allows thousands of tiny pressure pulses to bounce around in the main chamber, canceling each other out to some extent in addition to being absorbed by the muffler's housing.
Resonator or Muffler?
Some cars, especially luxury cars where quiet operation is a key feature, have another component in the exhaust system that looks like a muffler, but is called a resonator. The dimensions are calculated so that the waves reflected by the resonator help cancel out certain frequencies of sound in the exhaust system. The resonator contains a specific volume of air and has a specific length that is calculated to produce a wave that cancels out a certain frequency of sound.
Got questions about your vehicle's exhaust system? Contact an ASE-certified technician at one of our three Excel Auto Repair Shops. We will be happy to answer any questions about muffler. Check our website at www.excelautoandtire.com for the location closest to you. Our three auto shops are conveniently located in Eagan, MN, Spring Lake Park, MN, and Rochester, MN.
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