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I know that it quiets down the exhaust noise from a car /truck but does anyone know the scientifical aspect of what it does.
i know a bit about sound attenuation and how the sound waves are muted in the muffler and if you car is still too loud you can install a resonator but i want to know the science behind it
anyone with a background or career in this field ?

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Can'tfind a lot I disagree with in the previous replies, except the original idea I believe behind resonators was to reduce a specific frequency that original exhaust system was not reducing enough, and therefore by using a more narrow tuned "resonator", the tone or level could be changed or reduced.

However one thing not mentioned yet is, since acoustic energy in the exhaust is still energy, when the sound is reduced by cancelations, etc as described, that energy is then converted into heat, and hence one of the reasons mufflers are hot.