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F10 / F11 (2011 - Current)
The new chapter in the highly successful story of the BMW 5 Series Sedan (F10) and wagon (F11)

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  #1  
Old 03-26-2013, 09:48 AM
Kcustom Kcustom is offline
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1/4 wave resonator

I have done the research and measured the frequency band of the "drone" of my new exhaust system. Branch resonators seem to work very well based on what I have read. formula is:
Speed of sound @ 250 degrees (1260 / 120hz) / 4 = length of pipe..... if this works I will have the sound I was looking for and no Droan... : )
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Last edited by Kcustom; 03-29-2013 at 07:37 AM.
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  #2  
Old 03-26-2013, 05:59 PM
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dunderhi dunderhi is offline
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Now you are getting into Corsa territory. Good Luck!
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  #3  
Old 03-26-2013, 06:29 PM
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2.625 is the result, is this inches, feet? A stub of 2.625" is an easy fit, where would it connect or does it matter?

Or is this just the answer to "everything"?
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  #4  
Old 03-26-2013, 07:02 PM
Kcustom Kcustom is offline
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Quote:
Originally Posted by Donm View Post
2.625 is the result, is this inches, feet? A stub of 2.625" is an easy fit, where would it connect or does it matter?

Or is this just the answer to "everything"?
2.65 feet.... or roughly 31.5 inches.... caped on one end and T, ed into each exhaust runner. It can have bends just not sharp ones and needs to be towards the back half of the system... I have figured out drivers side and am working on pass side routing. I also welded on a new bracket tonight to relocate the gray rubber damper from stock muffler and eliminated most of the added droan below the resonance. See pic below. I also measured the cabin with an RTA and it showed this as well. Now to get geometry to work with the physics and I should have a great system (fingers crossed)
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Last edited by Kcustom; 03-26-2013 at 07:08 PM.
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  #5  
Old 03-26-2013, 07:06 PM
Kcustom Kcustom is offline
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Originally Posted by dunderhi View Post
Now you are getting onto Corsa territory. Good Luck!
Thanks... its kinda fun, tools , math and getting a little dirty for a change. Its been a while
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  #6  
Old 03-26-2013, 07:17 PM
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RTA? Db meter?

Very cool undertaking, keep us posted.
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  #7  
Old 03-26-2013, 07:44 PM
Kcustom Kcustom is offline
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Quote:
Originally Posted by Donm View Post
RTA? Db meter?

Very cool undertaking, keep us posted.
Real time analyzer... down loaded from play store (pro RTA) calibrated it using pink noise file. Then did 10 mins of driving at 45, 55, 65, and 75 mph. Logged peak frequency at each speed. Peak frequency was 110hz to 130hz at all speeds with average of 14db higher than cabin noise floor. Theory is if 1/4 wave resonator (filter) centered at 120hz, should attenuate drone by 10 to 12db.... I am also going to add another damper (BMW original part) to the other muffler
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Last edited by Kcustom; 03-29-2013 at 07:40 AM.
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  #8  
Old 03-26-2013, 08:26 PM
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Needsdecaf Needsdecaf is offline
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You seem like way too smart of a guy to keep misspelling drone...

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  #9  
Old 03-26-2013, 08:42 PM
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You seem like way too smart of a guy to keep misspelling drone...

Trust me, many scientists can't spell. I can only communicate in these forums with the help of auto-correctors.
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  #10  
Old 03-26-2013, 08:42 PM
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Great work!
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  #11  
Old 03-26-2013, 08:47 PM
Kcustom Kcustom is offline
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Darn auto correct... LOL... thanks
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  #12  
Old 03-26-2013, 10:32 PM
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I have been wondering if any 5er tried the drone free muffler: Dynomax VT

http://www.dynomax.com/mufflers.php?muffler=vt
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  #13  
Old 03-27-2013, 06:35 AM
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Needsdecaf Needsdecaf is offline
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Quote:
Originally Posted by dunderhi View Post
Trust me, many scientists can't spell. I can only communicate in these forums with the help of auto-correctors.
Hey, I R uh enguneer, so I can reelate!
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Heaven is where the police are British, the cooks are French, the cars are German, the lovers are Italian and it is all organised by the Swiss.

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  #14  
Old 03-27-2013, 07:55 AM
Kcustom Kcustom is offline
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Quote:
Originally Posted by BigDeep1 View Post
I have been wondering if any 5er tried the drone free muffler: Dynomax VT

http://www.dynomax.com/mufflers.php?muffler=vt
Would have loved to use their product, or Borla but could not find a muffler that would package. Our cars need a can about 13 inches long that will allow the inlet to be modified to a 45 degree angle. (rotated) thus the choice I made. I am just having fun with this and may change the entire system latter to a Borla system when avaliable, but in the meantime I am getting some guy time with my car
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  #15  
Old 03-28-2013, 03:26 PM
Kcustom Kcustom is offline
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got my crossover pipe in today and it fixed all that the damper did not except for the frequency that causes the drone.... now that is done on to the 1/4 wave pipes
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  #16  
Old 03-28-2013, 06:46 PM
Mbbrewer Mbbrewer is offline
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Love what you're doing. A Pioneer for us 550i guys with limited options for exhaust.
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  #17  
Old 03-28-2013, 10:14 PM
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This is a very fascinating thread. Strong work K.

What is your current muffler setup causing this drone issue? Also, was that "H-pipe" welded on at a specific measured location to tackle the wave length?
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  #18  
Old 03-29-2013, 05:19 AM
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K,
Is the drone emanating from the exhaust system at the tail pipe, a bouncing sound wave in the muffler system that comes through the floor, the header pipe or a sympathetic physical vibration of the exhaust system as a whole, like a tuning fork?

Never thought about its precise source.
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  #19  
Old 03-29-2013, 07:18 AM
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K-A K-A is offline
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Quote:
Originally Posted by BigDeep1 View Post
I have been wondering if any 5er tried the drone free muffler: Dynomax VT

http://www.dynomax.com/mufflers.php?muffler=vt
I looked into that but it seems none of their mufflers would fit an F10? They don't even have it listed in their cars list. In fact, after searching I couldn't really find ANY mufflers that fit an F10 that aren't accompanied with full catbacks and cost over like $1K (back in the day being into Mustangs spoiled me as you could get a great pair of mufflers for $50 each, weld them in, and it'll sound practically as good as any $500+ catback system).

Then again, there's an exhaust shop I know of that makes custom pipes so I'm sure they could make an ill fit muffler "fit", but I wouldn't want to take the chance.

I'd love a drone free exhaust. Though I'm skeptical. I would refuse to ruin the sound insulating experience of this car with a bassy drone at common RPM's. I remember riding in someone's Dinan tuned E60 545i a while back with an extremely droning exhaust and lowered suspension. When he'd hit that "sweet spot" in the exhaust (i.e max drone RPM range) note, you'd literally hear rattles in the car from the portions it presumedly helped wear out. That coupled with rattles attained from the hard riding suspension, the car sounded like a hooptie from inside and it was only a few years old.
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Last edited by K-A; 03-29-2013 at 07:21 AM.
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  #20  
Old 03-29-2013, 08:03 AM
Kcustom Kcustom is offline
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Quote:
Originally Posted by BigDeep1 View Post
This is a very fascinating thread. Strong work K.

What is your current muffler setup causing this drone issue? Also, was that "H-pipe" welded on at a specific measured location to tackle the wave length?
H pipe wes used to reduce some vibration I was getting around 88hz, location was selected on hi resistance location of exhaust measured by heat in pipe... drone is next, by fabricating branch resonators for each side. Space is so limited in our cars the the design is proving difficult, but I will get it figured out
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Old 03-29-2013, 08:16 AM
Kcustom Kcustom is offline
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Quote:
Originally Posted by Donm View Post
K,
Is the drone emanating from the exhaust system at the tail pipe, a bouncing sound wave in the muffler system that comes through the floor, the header pipe or a sympathetic physical vibration of the exhaust system as a whole, like a tuning fork?

Never thought about its precise source.
Its in the system, like a tuning fork (great analogy btw) you can see from the pic attached I have eliminated all the unwanted noise from the system with the damper and H pipe except for "drone" frequency. If my math is correct I should be able to reduce 120hz (center as range is 110 to 130hz) by 12 to 14db with 1/4 wave resonators... just need some time to get packaging figured out and get it built. BTW, I would have preferred a Himholtz resonator but there is just not enough room for the can
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  #22  
Old 03-31-2013, 12:52 PM
Kcustom Kcustom is offline
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Mock up in PVC complete... now to replicate it in metal an figure out hangers
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  #23  
Old 03-31-2013, 01:30 PM
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Can't wait for a photo from the ground with the car up on a lift!

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  #24  
Old 04-05-2013, 11:09 AM
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Drone is history..... : )
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  #25  
Old 04-05-2013, 03:04 PM
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BigDeep1 BigDeep1 is offline
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I can't wait to hear the sound clip! Congrats!!
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