Invidia mod: Helmholtz resonator (Exhaust booming)
12-09-2004, 10:58 AM
#11
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Last weekend I removed the resonator from my Invidia and swapped into place the stock resonator. The result=== much less droning. The car still sounds loud as hell, but the noise seems to be more to the rear of the car now, rather than in the cabin. All in all I am very pleased with the results. Pm me if you want any further info..
12-09-2004, 01:31 PM
#12
PLEASE DO THIS MOD!!!! If you don't, I will before spring. I think the Invidia is a sweet looking exhaust and is reasonably priced. I like it even more with the burnt tips. I work in a metal shop and it doesn't take much to cut a hole and weld on a piece of tubing. Even if it doesn't work on the first try, it's easy to cut off, patch the hole and try again. That being said, would anyone like to donate a sacraficial lamb? 
12-09-2004, 03:56 PM
#13
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Originally Posted by TalonTid,Dec 9 2004, 11:58 AM
Last weekend I removed the resonator from my Invidia and swapped into place the stock resonator. The result=== much less droning. The car still sounds loud as hell, but the noise seems to be more to the rear of the car now, rather than in the cabin. All in all I am very pleased with the results. Pm me if you want any further info..
The reason I intended to do a Helmholtz mod instead of the whole resonator was just to target the boominess in the midrange. I guess a standard in-line resonator box will naturally quieten the whole sound to some degree which is not part of the plan
12-09-2004, 03:57 PM
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Originally Posted by r_duff,Dec 9 2004, 11:55 AM
Is the Helmholtz pipe the little stubby dead-end pipe on the stock exhaust?
12-09-2004, 04:29 PM
#15
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Originally Posted by ImportSport,Dec 9 2004, 10:46 AM
As for adding the resonator to the exhaust, in some respects the resonant chamber gives the end result of a notch filter but what your actually doing is bleeding off the frequencies which would be subject to the placement of the branch pipe.
The location, diameter and depth of this pipe are all dependant upon the wavelength of the frequencies you are trying to attenuate. You cant really just slap an extra pipe on the exhaust and hope it works. Although this isnt saying that, it wont work.
The location, diameter and depth of this pipe are all dependant upon the wavelength of the frequencies you are trying to attenuate. You cant really just slap an extra pipe on the exhaust and hope it works. Although this isnt saying that, it wont work.
It seems this is kind of the same physics as blowing over the top of a milk bottle and hearing a sound. Our resonator pipe vibrates gas at a certain frequency which phases-out the same frequencies in the rest of the exhaust system.
Here are the measurements for the Helmholtz pipes:
Distance from cat to centre of pipe: Stock 240mm, Amuse 220mm
Length: Both 150mm
Diameter: Stock 45mm, Amuse 55mm.
Location: Is similar both on the Amuse and on stock pipe. Guess that is the best place to put it.
Diameter: Logic suggests the diameter should be the same as the original pipe or slightly less to make it easier to weld. (?) In any case, if we vary length (see below), diameter should not be so critical and in theory the larger diameter should have more 'effect' than a thinner one. Diameter is proposed at 55mm same as the Amuse.
# of pipes: We have not discussed the # of pipes. Presume it to stay at one, for the time being. Jetskis (search for SeaDoo) have pipe-organ type arrays of Helmholtz resonators to quieten the sound. At the least, using more than one pipe might be a future option if we want to get philharmonic about the whole idea
The key issue therefore is frequencies. We want our new resonator to hit just the booming in 3k-4k revs. We don't know the 'right' setting but there must be one. The only easily tunable factor therefore is:
Depth: Instead of welding on a fixed capped pipe, why don't we weld on say a 100mm open-ended pipe. Over the top of that, we fit a larger capped-pipe with slots cut in it, held on by a clamp. Then we can test, readjust and generally alter and tune the system until we're sure we've got the precise frequency which cuts the drone best on that particular system. Once the length is determined, further mods involve a simpler fixed welded pipe to the blueprint.
12-09-2004, 05:47 PM
#17
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I have to agree to those scratching their head as to why swap an Amuse for Invidia.. 
I have a dual amuse and if i wanted louder , i'd just go get an R1000 or use the current dual with a straight pipe and intake..
I have a dual amuse and if i wanted louder , i'd just go get an R1000 or use the current dual with a straight pipe and intake..
12-09-2004, 06:08 PM
#18
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Diameter: Logic suggests the diameter should be the same as the original pipe or slightly less to make it easier to weld. (?) In any case, if we vary length (see below), diameter should not be so critical and in theory the larger diameter should have more 'effect' than a thinner one. Diameter is proposed at 55mm same as the Amuse.
Depth: Instead of welding on a fixed capped pipe, why don't we weld on say a 100mm open-ended pipe. Over the top of that, we fit a larger capped-pipe with slots cut in it, held on by a clamp. Then we can test, readjust and generally alter and tune the system until we're sure we've got the precise frequency which cuts the drone best on that particular system. Once the length is determined, further mods involve a simpler fixed welded pipe to the blueprint.
12-09-2004, 07:03 PM
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Thinks ... All we need now is someone from Honda to chip in:
"Drone? What drone? We only put that little pipe on to stop it whistling at 8500 ..."
Must be somebody out there who knows what frequencies that thing was meant to block.
"Drone? What drone? We only put that little pipe on to stop it whistling at 8500 ..."
Must be somebody out there who knows what frequencies that thing was meant to block.