We all know that when a muffler fails, your car can potentially break noise ordinances! While the ‘vroom-vroom’ is rather cool, the fact of the matter is, if the throaty growl of a muscle car is not intentional – you likely need to take your vehicle for a full exhaust system check-up and BMW muffler repair in Everett to the foreign car service specialists in Everett, Lynnwood, Mukilteo, Mill Creek, Lake Stevens, Snohomish, Marysville, Arlington…
Have you ever pondered the simple elegance of a car’s muffler? A true engineering marvel, this sound dampening portion of the exhaust system relies on the science of sound waves to operate.
SCIENCE OF SOUND
Alternating bursts of air pressure (high and low) form a pressure wave that creates sound. The sequence of events:
- Exhaust Valve Opens – emitting a high pressure pulse which is released into the exhaust system
- Pressure Molecules Collide – the high pressure molecules collide with low pressure molecules present in the exhaust system
- Pressure Waves Travel – the stacked high and low pressure molecules create a pressure wave that travel through the exhaust system, forming a low pressure pocket behind the wave
- Sound is Created – the resultant pressure waves exit the exhaust system before the gases; creating a sound wave that flutters or vibrates your eardrum which in turn sends a signal to your brain that is interpreted as sound
The primary components of the sound wave that affect what you hear:
- Sound Wave Frequency – the frequency of a wave is how close together the peaks occur. A high frequency wave repeats more quickly than a lower frequency wave, resulting in a higher pitched sound. Conversely, waves with a low frequency emit a lower pitch sound. Specifically, the faster an engine is running, the higher the frequency of the sound wave emitted.
- Air Pressure Level – the amplitude, or height of a sound wave is determined by the pressure behind the wave. A sound is directly proportionate to the amplitude (height) of the sound wave – in English: higher air pressure = increased amplitude = louder sound
A muffler is designed to combat excessive noise by using opposing sound waves to partially cancel each other out – how simply elegant is that?
The eardrum can only process 1 pressure at a time. All the sound waves created at a specific moment in time are essentially added together to produce a single wave to your eardrum. This scientific fact is how sound is effectively reduced with the addition of more sound waves! Sound waves, when visualized on an oscilloscope occur as sine waves as shown:
- Constructive Interference – when 2 or more sound waves are in phase (equal amplitude, frequency and direction of flow), the waves are combined or amplified to make the resulting sound louder.
- Destructive Interference – when 2 or more sound waves are exactly out of phase (amplitude and frequency are equal, but the direction of flow is opposite); when the out of phase waves are combined, they are in effect subtracted, resulting in cancellation (in a perfect world) or decrease of the resulting sound.
Using the destructive interference technique, mufflers are designed to subtract as much resulting sound as possible from the pressure waves created by the car’s exhaust.
An automotive muffler is comprised of the following:
- Inlet Pipe
- Main Flow Chamber
- Resonating Chamber
- Perforated Tubes
- Outlet Pipe
As the cutaway shows, the exhaust flows into the main chamber, then a portion of the waves are forced into the resonating chamber through a hole in the baffle wall. As the waves pass through the hole, they are broken and the remainder of each wave flows through the resonator. The portion of the sound waves that pass through to the resonating chamber bounce off the back wall, resulting in phase reversal; as the converted waves pass back through to the main chamber, they cancel out (theoretically) each new pressure wave that is passing into the resonating chamber.
The resonating chamber for each muffler is carefully designed to allow the (hopefully) perfect length that the waves need to travel to intersect properly. This is but 1 type of muffler, some are simple in-out with a glass insulation wrapping to absorb the sound waves. Ask the BMW muffler Everett Experts for advice/inspection/repair/replacement in Everett, Lynnwood, Mukilteo, Mill Creek, Lake Stevens, Snohomish, Marysville, Arlington regarding the specifics of your vehicle’s muffler.
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