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Originally Posted by mr_robot
I will add the water leaked very easily. I used a 20oz cup and could pour it all without over flowing.
This is surely an engineered resonator not just muffle sound but provide something they wanted to achieve.
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Exactly!
Found another excellent nerd article here:
https://www.rodauthority.com/tech-st...on-strategies/
This resonator is designed to eliminate sound with the insulation around the holes. The engineer's (well, BMW marketing folks) unwanted sounds are absorbed into the insulation while the waves mix with each other and cancel one another out. This isn't a great picture since it shows only one inlet, but if you consider that this happens inside the unit, you have a clear idea of the design purpose. One set of sound comes in from the motor (blue) and hits the insulation as it flows through the holes. If we add another inlet doing the same thing and removing the noises from that bank, you get two inlets with different sound being filtered.
The audible result is the yellow arrows representing the desired sound.
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Absorptive mufflers are designed so that the sound entering the muffler interacts with packing material and is converted to heat by the frictional process. This muffler’s performance relies on absorption by the packing material for performance.
Absorptive type mufflers gained serious recognition in the late 50s by hot rodders and have continued to thrive with enthusiasts that want a very aggressive high performance sound. These straight-through designed mufflers produce a tantalizing sound and are sought after by many enthusiasts.
Enthusiasts wanting an absorptive style muffler should look to choose one from a reputable manufacturer like the ones that we have listed here. “Certain mufflers can burn out because the packing material is in contact with perforated tubes and the hot exhaust gases,” said Benty. If the packing material burns out or is blown out of the muffler, it’s ability to provide any noise control is reduced.
Absorptive type mufflers tend to be a straight-through style core wrapped with a packing material for sound absorption.
“Absorptive muffler technology has been around since the 1950‘s,” explained Tauber. “The problem with this technology is that even though the muffler looks straight through, the turbulence caused by the sound and exhaust pulses trying to escape into the packing material, causing back pressure.”
“The quietest time in an absorptive muffler’s life is when you buy it,” says Flowmaster’s Nate Shelton. Shelton has over 40-years of experience with performance exhaust since starting at Hooker Headers in 1972.
As Benty explained above, the packing material gets burned or blown out of the muffler. Condensation can soak into the packing material adding to the degradation of the muffler’s ability to act as a silencer. Unless you plan on replacing your mufflers a lot more frequently, or wearing noise canceling headphones when you drive, straight-through mufflers may not offer the controlled sound level that you desire.
Sound waves move to the exterior though the packing material on it’s way out of the muffler. Many enthusiasts like the sound created by this style muffler.
Noward explained absorptive muffler’s perforated tubing as being a big difference between the reactive style and absorptive style muffler design. “We don’t use porous tubing as a primary means of sound deadening as this type of methodology is generally used with a packing muffler as the primary means of sound deadening. These methods can actually impede flow.”
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