We’ve all heard them—cars coming down the street, sounding more like the charge of an Army brigade than a vehicle. The pops and bangs blow out like gunfire. You almost want to seek shelter as fast as possible until cooler heads prevail. Still, Chicago muffler sounds can be very disconcerting, whether in Lincoln Park or the most dangerous projects.
What exactly causes the sound? Explosions from gas in the engine propel the car. Lighting the gas using the spark plugs starts the combustion cycle. Pistons get going and they turn the crankshaft, which eventually rotates the tires and gets the car moving. But that’s all beside the point. The key word in the previous material is “explosions.” If you’ve been to war or seen war movies, you know they are loud. The muffler’s job is to silence the sound as much as possible.
You may think insulation is used to stifle the noise. That’s an incorrect assumption. It’s actually a complex process using the physics of sound.
Noise comes at us in waves. All the sound waves hitting your ear at once is what you hear as a result. No matter what’s coming in—be it music, voices, and/or dogs barking—since everything’s all added together, the ear drum only feels one pressure at any given moment. The culmination of all these sounds is called constructive interference. If sound waves are out of phase, they cancel each other out, thereby becoming a straight line again. This phenomenon is known as destructive interference.
According to HowStuffWorks.com, mufflers are made to create waves that cause as much destructive interference as possible. Inside a muffler is a set of tubes with holes in them. Wouldn’t you think that noise would come pouring out of these holes? Actually, they are designed to reflect the sound waves produced by the engine in such a way that they partially cancel themselves out.
This happens as the sound bounces back and forth through the muffler, directed through certain holes until it ends up in the resonator. If you think of a resonator as a child’s tide pool you can visualize the reaction. As waves flow across a pool, they hit the wall and bounce back. When these reflected waves crash into oncoming waves, they mingle and knock each other down. Soon, the little rubber ducky toy floating on the surface isn’t tossing about anymore because the water has become flat. Or at least mostly flat. What remains of the waves is the sound you hear.
That is a lot of steps for noise to go through before you hear silence. However, you must remember that the sound waves move much faster then water waves as mentioned above. That happens to be around 760 miles per hour. So there’s plenty of time for this to happen.
The main reason for muffler noise is when a new hole is added to the mix, whether from rust or from hitting an object like a bouncing stone. Sound escapes through this new opening and throws all the described physics out of whack. Tape is a temporary solution, but at that point, the only real solution is to replace the muffler.
