What does a resonator in an exhaust do that is different?

[me3@neuralfibre.com]

Got a beaudesert 3" system put on the other week.

I declined the resonator, as I am happy with a little more noise, although a 3" mandrel w/ straight through performated is much louder than a 2.5" with the same setup.

BUt I do wonder - what exactly does a resonator do that makes it different from a muffler?
When I looked at the inside of it - it looked like a straight through perforated can to me.

Thanx
Paul

[GUtripper]

Like the name says, removes the resonance.
It wont necessarily make it quieter, but will/should remove the drumming/thrumming at highway speeds and make things quieter in the cab.

[bazzle]

Diff lengths, directions can be tuned to remove particular frequencies.

Bazzle

[80's_delirious]

all the litlle perforations are to confuse the sound waves, as some of the wave will bounce back, some will pass through the perforations. Instead of exhaust sound coming out in smooth pulsing waves, the sound wave is broken into a mess which cancels out some of the resonating pulses.

[tweak'e]

resonator is a fairly loosely used term.

a true resonator would be fairly rare to find on a car exhaust. i think one of the cortinas had one on the rear. its basically a offset muffler with nothing in it, no baffles no perforated pipes.....nothing.
most vehicles have them on the intake system ie the funel shaped pipe on a carby aircleaner or empty box fitted on the side of the intake pipes.

the problem with a proper resonator is they resonate. they dampen out a range of frequencies but amplify their natural resonate frequency.

what most call a resonator is just a straight through perforated can, which is just another style of muffler.

personally i like to fit a straight through muffler/resonator simply to get the exhaust to sound nice.
different types of perforated tubes and different ends to the muffler change the sound so there is a fair bit you can play with.
if you have the time get them to fire the engine up and listen to the different ones.

[-Nemesis-]

Diff lengths, directions can be tuned to remove particular frequencies.

Bazzle

Is there a way to work out the frequencies/designs needed?

Mine drones between 2900-3100rpm but is crisp as everywhere else. Though, I'm sure it's come with age so it could be the old cat or main 3" muffler.

[rowenb]

Made my own mufflers/resonators recently, drilled a shit load of holes in some 2 1/2 inch pipe, wrapped some insulation round it and sheetmetal over that, fully welded out of ss. The first one was made for my 80 but now want a 3 inch on it so slapped it my commodoore with two other small ones before the bigger one at the rear. Was really surprised how they turned out, nice note at idle, burbles nice with a heavy foot and quiet at 100kms. Pretty good for a V6 but does drone when taking off and under light accelleration. Will deffinately make a 3 inch one for 80 when the time comes and will make a complete stainless system from dump pipe.

[bazzle]

Diff lengths, directions can be tuned to remove particular frequencies.

Bazzle

Is there a way to work out the frequencies/designs needed?

Mine drones between 2900-3100rpm but is crisp as everywhere else. Though, I'm sure it's come with age so it could be the old cat or main 3" muffler.

http://www.custom-car.us/exhaust/default.aspx

[me3@neuralfibre.com]

So from the sound of it - unless a resonator is "tuned" for the "problem" it's probably not going to be significalty different from a muffler.

If both are straight through, perforated, glass packed - they are pretty well both mufflers although maybe with different behaviours due to size / density differences.

Paul

[fester2au]

I've heard people play with what I would describe as an expansion chamber even though we are not talking 2 stroke technology here. Placing a bigger bore section of pipe in the system can change the dynamics by slowing the exhaust gas down without actually having any muffling hardware at all but ?I have no idea if there is any science to calculating this or they just whack a few sections in and try them all. I was going to test sticking say a 4 or 5" section into my straight through non muffled 3" just to see what if anything it did. Don't forget location of exhaust tip as well as shape and where it is pointing can also have an effect on exhaust noise.

[chimpboy]

From a google search:

Resonators: The body of a resonator is constructed in three layers: Two thin layers of metal with a thicker, slightly insulated layer between them. This allows the body of the muffler to absorb some of the pressure pulses. Also, the inlet and outlet pipes going into the main chamber are perforated with holes. This allows thousands of tiny pressure pulses to bounce around in the main chamber, canceling each other out to some extent in addition to being absorbed by the muffler's housing. Its dimensions are calculated so that the sound waves reflected by the resonator help cancel out certain frequencies of sound in the exhaust.

Regular Mufflers: Located inside the muffler is a set of tubes. These tubes are designed to create reflected waves that interfere with each other or cancel each other out. The exhaust gases and the sound waves enter through the center tube. They bounce off the back wall of the muffler and are reflected through a hole into the main body of the muffler. They pass through a set of holes into another chamber, where they turn and go out the last pipe and leave the muffler. But creates backpressure in doing so, good for torque, but not good for power. There is also a chamber called a resonator that is connected to the first chamber by a hole. The resonator contains a specific volume of air and has a specific length that is calculated to produce a wave that cancels out a certain frequency of sound. Yes a regular muffler has a portion of its area designed as a resonator.

Low Back Pressure - Glass Pack Mufflers: There are other types of mufflers that can reduce backpressure. One type, uses only absorption to reduce the sound. On a muffler like this, the exhaust goes straight through a pipe that is perforated with holes. Surrounding this pipe is a layer of glass insulation that absorbs some of the pressure pulses. A steel housing surrounds the insulation.
I had an old Capri that had a 'hot dog' resonator in the middle and a high flow muffler on the back, low revs was a real rumble, but in highway revs it was real quiet. (resonators work on specific sound waves which are affected by revs) Hope this helps.

http://forums.bimmerforums.com/forum/sh ... p?t=439890

Note he says a muffler has a resonator section built in; this is what howstuffworks says as well. http://auto.howstuffworks.com/muffler4.htm

Other than pasting that in I have nothing to add

[fester2au]

Yes so now I remember the resonators that my local exhaust guy used to use that did all my cars. Worked well and the one time I had to get repairs done somewhere else they didn't use them and it sounded like crap. Can't remember the brand but basically it was just like a straight through muffler except the perforated tube did not run all the way through it had a section cut out of the middle so you had an entry pipe and an exit pipe but they were not joined even though they were in alignment. Pipe was packed and from memory there was no end cap or diverter on the inner end of each pipe segment rather they were capped outwardly from the tube to the outer of the shell forming a chamber around each perforated section of pipe but not stopping exhaust gas from exiting straight through. So the middle section was again a bit like an expansion chamber.

[tweak'e]

Resonators: The body of a resonator is constructed in three layers: Two thin layers of metal with a thicker, slightly insulated layer between them. This allows the body of the muffler to absorb some of the pressure pulses. Also, the inlet and outlet pipes going into the main chamber are perforated with holes. This allows thousands of tiny pressure pulses to bounce around in the main chamber, canceling each other out to some extent in addition to being absorbed by the muffler's housing. Its dimensions are calculated so that the sound waves reflected by the resonator help cancel out certain frequencies of sound in the exhaust.

Regular Mufflers: Located inside the muffler is a set of tubes. These tubes are designed to create reflected waves that interfere with each other or cancel each other out. The exhaust gases and the sound waves enter through the center tube. They bounce off the back wall of the muffler and are reflected through a hole into the main body of the muffler. They pass through a set of holes into another chamber, where they turn and go out the last pipe and leave the muffler. But creates backpressure in doing so, good for torque, but not good for power. There is also a chamber called a resonator that is connected to the first chamber by a hole. The resonator contains a specific volume of air and has a specific length that is calculated to produce a wave that cancels out a certain frequency of sound. Yes a regular muffler has a portion of its area designed as a resonator.

Low Back Pressure - Glass Pack Mufflers: There are other types of mufflers that can reduce backpressure. One type, uses only absorption to reduce the sound. On a muffler like this, the exhaust goes straight through a pipe that is perforated with holes. Surrounding this pipe is a layer of glass insulation that absorbs some of the pressure pulses. A steel housing surrounds the insulation.
I had an old Capri that had a 'hot dog' resonator in the middle and a high flow muffler on the back, low revs was a real rumble, but in highway revs it was real quiet. (resonators work on specific sound waves which are affected by revs) Hope this helps.

IMHO a bit of BS.

whats the difference between the resonator description and the so called Low Back Pressure - Glass Pack Mufflers......nothing.

once you start adding perforated tubes or glass packing etc you have turned a resonator into a muffler.

end of the day its just BS speak. people call things whatever they want. eg a straight through muffler/resonator is commonly called a "hot dog" or "coby".
once i ask the local exhaust shop to fit a straight through muffler and they fitted a bit of exhaust pipe instead of a muffler FFS !