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Exhaust drone, (Now Solved)

Ben! Sep 27, 2018

  1. Ben!

    Ben! Member Supercharged Audi S4 Audi Avant Owner Group DSG

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    Ok so thought I was being clever. Copied the layout of an off the shelf performance exhaust with a hand made system. Wow what a mess up. The car is now undrivable. Drone is insane. Budget tight I can’t afford to start again so am looking for a tried and tested sure fire fix. So all input welcome.
     
    Last edited by a moderator: Sep 27, 2018
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  3. jdp1962

    jdp1962 Grumpy Old Man TFSI Owners Group Team V6 Gold Supporter Team Tornado Audi S4 Black Edition quattro S tronic

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    If you still have the old exhaust, is it useable? Can you put it back on ?
     
  4. DieselJake

    DieselJake Well-Known Member VCDS Map User

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    Which engine do you have? What does it have in terms of back boxes, silencers, emmisions stuff? Might get away with just adding stuff to quieten it down.

    Do the rear tips come out further than the bumper? Some people suffer more noise if they are tucked in a bit.
     
  5. Ben!

    Ben! Member Supercharged Audi S4 Audi Avant Owner Group DSG

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    Car is an S4 Avant DSG. I have X pipe at front combined box where the factory one was and a back box each side at the back. Sound is fine not too loud. Outside car great. Inside when shifts up at low rpm it’s unbelievable. It hurts your ears!
     
  6. I oOEddOo I

    I oOEddOo I Active Member Team Ibis Supercharged TFSI Owners Group Team V6 Audi S5 Black Edition quattro

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  7. youngsyp

    youngsyp Active Member Team Monsoon Supercharged Audi S4 Audi Avant Owner Group Black Edition S tronic

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    On the OE system, there are resonators in the mid section and back boxes, which neutralise the natural resonance of the exhaust gas passing through the exhaust syste,. By removing these, you have nothing in the exhaust system to counter the resonance. Silencers or mufflers will have no effect, which is what you'll have fitted where the OE mid and back boxes were. The only way to neutralise the resonance is to install appropriate resonators. Getting that right will require experimentation, for size and location.

    This is where you come to appreicate just how much time, effort and money OEMs put into the exhaust systems fitted to these cars.

    He mentioned changes to the exhaust system itself, reducing drone. And adding the sound reduction measures to improve the stereo. Sticking deadening mat to the body will not affect exhaust drone in anyway. It will just reduce the car body resonating as a result of extra noise the exhaust is producing.

    You could add mass to the exhaust itself to reduce the drone but I suspect you'd need to add a lot to have any real impact.

    Paul
     
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  8. Super Solo

    Super Solo New Member

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    Hi.

    I've an A4, B8, 3.2 Quattro, on which I recently had the exhaust modified.

    Initially I was going to remove the two smaller resonators, mid system. But after further research I decided to leave the resonators on the car, but remove the OE silencers and in their place were fitted a small straight through silencer each side. I too now have a dreadful drone between 1800 and 2700 RPM, in the higher gears.

    I've applied some sound insullation to the rear floor, under the carpet, but to little effect.

    My next step is to try to attach a 500g mass to each new rear silencer, hoping some inertial damping will erradicate the drone/resonance.

    If I get any significant results, I'll try to post back.
    Sorry I'm not much more help, perhaps my experience will be food for thought, for others who have not yet gone this route, but are considering it?
     
  9. Meemo

    Meemo Well-Known Member Supercharged Audi S5 Black Edition

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    in addition to the resonance pads and the MLV boot lining matt, EMP Performance put 2 inserts in the 2 of the 4 pipes after the cat, the inserts are simply curved pipes (bit like a ladies waist curves in) to reduce the speed of the exhaust gasses. This combination means i still have a very lovely burble, car is prob on the antisocial side for noise level outside (but i kinda like that), I do still get drone but only when under load like accelerating up a hill, nothing at 70, you would think it was stock when cruising.

    Sadly the drone because it happens only under load, means it over bears that lovely burble of the v if I am driving it with a slightly heavier foot, but pootling around i love it i.e. accelerating like most common folk, and foot flat sounds really angry, love that. I must say though for 1k its far better than what some offer, and EMP will always provide further solutions if I am not happy, as it is now it is fab for what i paid.
    However if you want no drone atall, you have to fork 2.5k for the awe set up which is very well tested and highly favoured.
     
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  10. youngsyp

    youngsyp Active Member Team Monsoon Supercharged Audi S4 Audi Avant Owner Group Black Edition S tronic

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    It won't have any effect. You need to add mass to the pipe work.

    Paul
     
  11. arad85

    arad85 Well-Known Member Team V6 Audi S5 Black Edition

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    IMHO, drone comes from the exhaust exciting the resonances in the cavities in the car (look up standing waves if you need to see the physics), not exciting resonances in the panels. This means if you want to eliminate drone, you have to do it in the exhaust, not the panels. Whilst mass-loading the panels will have some impact as they then add less to the noise, the fundamental issue is - IMHO - cavity size. Not a lot you can do about that except to eliminate it at source. This means if you want less drone, you have to figure out what frequency is making the resonance and eliminating that from the exhaust. Depending on your car, the dimensions of the resonator (your boot) wil be different. My S5 has a boot around 1m x 1m x 45cm. Which means if I want to eliminate drone I need to be eliminating frequencies around 330Hz and 700Hz. The consequence is a couple of resonators in the exhaust at those frequencies. I have a AWE touring with resonated pipes and it still doesn't eliminate it so 1800rpm on an uphill climb is loud - which is what @Meemo is hearing.

    Bottom line is basically, OEM is tuned to get rid of as much as possible. Anything else is a compromise. Live with it or go OEM.
     
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  13. PenttisHSR

    PenttisHSR Active Member Audi S4 Audi Avant Owner Group Manual

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    Put the back boxes back on, they are both resonators.
    You can weld your own (bigger?) tailpipes on before you fit them for looks.
     
  14. ianv5

    ianv5 Active Member TeamMisano Team V6 Audi S4 Audi Avant Owner Group quattro

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    Bcs backboxes might help?
     
  15. Ben!

    Ben! Member Supercharged Audi S4 Audi Avant Owner Group DSG

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    Ok so skimming the forum this has been covered before. Not clear though if anyone solved the issue. I getting mixed suggestions.
    1)Remove x pipe fit two resonator
    2)Install two resonator on down pipes before x pipe
    3)Fit baffled boxes at the back.
    Your thoughts and advice are appreciated.
     
  16. Meemo

    Meemo Well-Known Member Supercharged Audi S5 Black Edition

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    got a video of it currently? only for curiosity :)
     
  17. youngsyp

    youngsyp Active Member Team Monsoon Supercharged Audi S4 Audi Avant Owner Group Black Edition S tronic

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    As mentioned above, the OE system has 4 resonators in it of different sizes/ designs. One in each of the 'front' pipes and one in each of the back boxes. With your current design, there's no need to remove the X pipe, incorporating a pair of resonators in the front pipes to work with it, would have an effect. You could buy the Magnaflow resonated X pipe, to replace your non resonated X pipe.

    There's no point fitting 'baffled' boxes in the rear section either. Baffling is a form of silencing (reflection) and will not help with drone. Silencers dictate the volume of an exhaust, whilst resonators dictate the tone of the exhaust.
    What you need is a back box each side with an approriate resonator included in it's design. This could be tricky to find. If you want volume however, fit a resonator in each branch instead of a silencer/ resonator.

    To be methodical and reduce the outlay possibly, you could try fitting a single resonator in each branch and see how it sounds from there.

    Paul
     
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  18. Ben!

    Ben! Member Supercharged Audi S4 Audi Avant Owner Group DSG

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    Update, two new resonators fitted where the old factory ones were. No difference. Overall volume lower drone as before. £200 lighter still undrivable!
     
  19. Meemo

    Meemo Well-Known Member Supercharged Audi S5 Black Edition

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    are you unable to put the old ones back in place?
    I know EMP said the 3.0 v6s had awful drone, and they found the way they routed the pipes to have an affect on the overall drone.
    Mine is certainly driveable. this is my set up if it helps:
    CAT back
    dual piped until the centre box, after which it is 2 singles.
    2 Cone inserts between the cats and mid box

    [​IMG]
     
  20. youngsyp

    youngsyp Active Member Team Monsoon Supercharged Audi S4 Audi Avant Owner Group Black Edition S tronic

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    Sounds like the resonators in the back boxes do most of the drone reducing work then.

    Paul
     
  21. miltybilty

    miltybilty Active Member

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    Try using vibrant ultra quiet resonators ....

    Vibrant is based Canada so you will have the dollar/pound on your side I believe.

    Vibrant ultra quiet is highly recommended by everyone who uses them.

    Do you have a picture of your exhaust?
    Even a drawing?

    Also you could use dynamat in the back where the spare wheel is usually.

    Now here is a red green idea .... Although it should work. A few Shipping Blankets in the back of your car.


    Also make sure you have stock from resonators on your car still .... I think X-Pipe placement matters as well.

    Lots of people use the magnaflow resonated X-Pipe.

    https://www.google.ca/search?client...j8......0....1j2.......3..41j0i67.uu_txGHUMl4

    Google search showing some good results.

    Sent from my DEVICE using Tapacar
     
  22. PenttisHSR

    PenttisHSR Active Member Audi S4 Audi Avant Owner Group Manual

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    I told you already, you need to refit the OE Back Boxes.
    They are resonators, [HELMHOLTZ chambers] specifically designed to eliminate that specific drone.
    I know this because I have been through it! I posted photos of one cut open on here before.
    They will not cost you any power and you can weld your own tailpipes on for looks.
     
  23. miltybilty

    miltybilty Active Member

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    Eh you got that picture you could pm me?

    I'm genuinely interested how they make the rear S4 mufflers.

    Would you know if an x pipe in place of the centre resonator would cause too much drone on a sedan S-TRONIC?

    Thanks

    Sent from my DEVICE using Tapacar
     
  24. PenttisHSR

    PenttisHSR Active Member Audi S4 Audi Avant Owner Group Manual

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    I posted a pic in your own thread
     
  25. Ben!

    Ben! Member Supercharged Audi S4 Audi Avant Owner Group DSG

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    Ok so update time. Drone gone. For those interested. It would appear the only way to get rid of the drone is to basically replicate the factory exhaust. So in short:
    1: X pipe gone. All the guff about it helping is just that. Makes exhaust note sound great but does nothing for drone.
    2: Front resonators help reduce volume which in turn contributes to end solution but is by no means a fix on their own.
    3: The factory boxes contain Helmhotz resonators for a good reason. ( As posted by Chop)
    4: Without a phd in acoustic engineering simplest solution I have found is Tri Flow silencers

    System is now:
    2.5" pipe T304 Stainless
    Straight through 14" resonators
    Centre box two in two out
    Rear Tri flow resonators
    Twin 80mm tail pipes

    An expensive lesson learnt. Car is so quiet now. Not what I wanted originally but drone free so I am more than happy. Bigger bore should help with later stage 2 plans so not a total loss.

    I have for sale after all the trial an error if anyone is interested a 2.5" stainless X pipe and two straight through resonators. Half an exhaust basically!
     
  26. Ben!

    Ben! Member Supercharged Audi S4 Audi Avant Owner Group DSG

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    Photos of final set up.
     

    Attached Files:

  27. bobby singh

    bobby singh BSR VCDS Map User TDi Audi A4 quattro

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    This is exactly the reason why my hand made 3" is collecting dust in the workshop..It was driving me nuts.
    Must be age related :)
     
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  28. Ben!

    Ben! Member Supercharged Audi S4 Audi Avant Owner Group DSG

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    Agreed.10 years ago ok maybe 20 years ago I'd have loved it in its first incarnation. Loud nice V6 warble pops on shift and overrun. Every time it droned foot down or stereo up and sod the Mrs. These days not so Mrs gets her way as she been around a while now. Plus kids come into play I think the next parents evening my youngest would rather have walked. How life changes!!
     
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  29. bobby singh

    bobby singh BSR VCDS Map User TDi Audi A4 quattro

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    Ben let me guess 70's child :)
    I know the feeling mate - I have the same - doing 20k a year i rather have comfort than a ringing head.
     
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  30. Ben!

    Ben! Member Supercharged Audi S4 Audi Avant Owner Group DSG

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    Correct. I guess the whole process is to satisfy our inner child we are still young at heart! Still I'm sure you'll agree there's something to be said for a sleeper. A circa 400bhp family estate surprises a few youngsters at the lights. Until the Mrs says slow down even though she's smiling!
     
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