The Physics Behind Chamber Muffler Designs
Automotive muffler designers use sound physics to reduce the amount of noise coming from automobile exhaust systems. The designers use sound wave interference to cancel out noise. In this article we will explore the concept of sound wave interference and see.Get more news about
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how muffler designers put to it to work.
Constructive & Destructive Wave Interference
There are two types of sound wave interferences: constructive and destructive. Constructive interference is two waves having the same frequency and being in-phase. In-phase means that the crests of each wave are in alignment (see the first diagram below). When this happens amplitudes are added together creating a more powerful wave.
An example of this would be at a rock concert. Imagine you are at a Bob Seger concert, sitting 25 rows back on the right side of the stage. In front of you are two giant speakers. One speaker is situated on top of another speaker. Both speakers are sending out identical sound waves. This is an example of constructive interference. The waves are considered in-phase: the crests of each wave line up with one another. Here the amplitudes are added together in essence doubling the power of the wave.
If one speaker was set back a bit, approximately ½ a wave length, then the crest of one speaker’s wave will line up with the trough of the other speaker’s wave and vice versa. These waves are said to be out-of-phase. The two amplitudes will cancel each other out and there will be no sound. This is destructive interference. This concept is used in most car mufflers to cancel the exhaust sound waves.
The top diagram shows two waves in-phase traveling in the same direction. The two wave crests and troughs are aligned. The two crests add together to form a supercrest and the two aligned troughs form a supertrough. The two waves in the second diagram are out-of-phase. The crest of one wave matches the trough of the other wave and vice versa. The amplitudes here cancel each other out - the sound in this case disappears. Muffler designers use this concept when designing chambered mufflers.
Waves Traveling in Opposite Directions
Waves traveling in opposite directions towards one another will momentarily affect each other and then pass through as if nothing has happened. Looking at the diagram below we see wave A about to intersect with wave B. When they do intersect, the amplitudes are briefly added together and then pass one another as though nothing has happened. These two are briefly in phase. Likewise, two out-of-phase waves traveling in opposite directions towards one another briefly cancel each other out.
Below is a diagram showing two waves moving towards each other. Here the sound gets louder for moment at their meeting point as the amplitude doubles. After they pass through each other and continue onward it is like nothing ever happened.
The Physics Behind Chamber Muffler Designs
