Exhaust drone, (Now Solved)

Ben!

Registered User
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.
 
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jdp1962

Grumpy Old Man
If you still have the old exhaust, is it useable? Can you put it back on ?
 

Ben!

Registered User
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!
 

youngsyp

Registered User
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.

Hi Ben,

Have a read on the below link scroll half way down the page @Meemo has installed some pads to reduce the drone maybe it can help you a little.

https://www.audi-sport.net/xf/threads/mandas-s5.359280/page-2
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
 

Super Solo

Registered User
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?
 

Meemo

Registered User
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.
 

arad85

Registered User
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.
 

PenttisHSR

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

Ben!

Registered User
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.
 

youngsyp

Registered User
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.
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
 

Ben!

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

Meemo

Registered User
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

39707673142_157d349f3c_b.jpg
 

youngsyp

Registered User
Update, two new resonators fitted where the old factory ones were. No difference. Overall volume lower drone as before. £200 lighter still undrivable!
Sounds like the resonators in the back boxes do most of the drone reducing work then.

Paul
 

miltybilty

Registered User
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.
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
 

PenttisHSR

Registered User
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.
 

miltybilty

Registered User
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.
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
 

Ben!

Registered User
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!
 

Ben!

Registered User
Photos of final set up.
 

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Ben!

Registered User
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!!
 

Ben!

Registered User
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!
 

Seanelliott2001

New Member
Photos of final set up.
I have been
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!
Hey Ben! I have been chasing the same problem sadly:( could you tell me what the names of the silencers and center box you bought?
 

Ben!

Registered User
Sorry to hear you are having the same troubles. I have unfortunately sold the car now so I cant provide photos. I can however confirm all the parts were long life items.
 

Seanelliott2001

New Member
Sorry to hear you are having the same troubles. I have unfortunately sold the car now so I cant provide photos. I can however confirm all the parts were long life items.
Thank you for the response! Do you know the brand of resonators and center box you had installed?
 

Ben!

Registered User
That' is the make. Long life. To be honest once i bought all the parts to make it drivable without your fillings falling out it would have been cheaper to order the scorpion no- drone exhaust.
 
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