Cure for the Drone?

[bklounge]

Originally Posted by RaptorKTM

Get an Akrapovic Exhaust. My full down pipe back system is better then any factory system ive heard. And no Drone on freeway at all even with the dumps open.

How's the volume with the dumps open at freeway speed?

[RaptorKTM]

At 70mph the car is quiter then stock with or without the dumps open. With it closed it is quiter in general. With the dumps open if you give any throttle to lets say pass or change lanes, then it will for that period become louder. The Akrapovic is more civilized then stock when you want it to be, and more of a crazed lion. Best of both worlds.

[James T. Kirk]

Originally Posted by Mr.Metak2you

Just ignore the unproductive useless comments. People who say there is no drone in this car probably think the world is flat and there is no such thing as gravity. I have no issues with some saying it doesn't bother them or they like it but to say it doesn't exist, is just a classic case of 'ignorance is bliss.'

The drone is measurable. I am currently attempting to nail down the exact frequency at ~2300RPM in 6th. I'm trying to get a good recording to capture and analyze. I was planning on doing a thread for those looking for a solution to the drone. There is an equation that you can use to calculate the length of tubing(closed end Helmholtz chamber) to weld inline prior to the exhaust that will not affect airflow(air will not pass through) but will absorb the drone causing frequency. (on my phone currently and don't have the equation handy) The diameter will be the exact same as the existing OEM piping. The exhaust will sound pretty much exactly the same across the entire frequency spectrum except for the specific drone frequency.

Do your thang, Spock!
.

[rapter]

Originally Posted by RaptorKTM

At 70mph the car is quiter then stock with or without the dumps open. With it closed it is quiter in general. With the dumps open if you give any throttle to lets say pass or change lanes, then it will for that period become louder. The Akrapovic is more civilized then stock when you want it to be, and more of a crazed lion. Best of both worlds.

How much $$$$$

[1M Fan]

I'm subscribing to this thread.

[ChrisBuer]

Milltek have developed a system that eliminates the drone but makes the car quieter as a result.

[wan888]

I think there used to be a company call Europipe ... they offer 0 resonance for the 996 GT2 back many years ago ... not sure if they do the same for BMW.

[wan888]

There you go:
http://www.europipe.be/index.html

[v1k0d3n]

Originally Posted by Mr.Metak2you

Just ignore the unproductive useless comments. People who say there is no drone in this car probably think the world is flat and there is no such thing as gravity.

The drone is measurable.

I was planning on doing a thread for those looking for a solution to the drone. There is an equation that you can use to calculate the length of tubing(closed end Helmholtz chamber) to weld inline prior to the exhaust that will not affect airflow(air will not pass through) but will absorb the drone causing frequency.

Metak, agreed (on first point), agreed (on second point) and can't wait to see your thread. If you don't play the stereo at high volumes it can be pretty damn annoying. I noticed this a lot when christmas shopping with my girlfriend this weekend. It was distracting, and even though she doesn't seem to mind a lot, it really bothered me. I'd be interested in a way to cancel out the drone on the stock system (a productive solution).

[b33g33]

Originally Posted by v1k0d3n

Metak, agreed (on first point), agreed (on second point) and can't wait to see your thread. If you don't play the stereo at high volumes it can be pretty damn annoying. I noticed this a lot when christmas shopping with my girlfriend this weekend. It was distracting, and even though she doesn't seem to mind a lot, it really bothered me. I'd be interested in a way to cancel out the drone on the stock system (a productive solution).

Seconded.

I noticed this the most while schlepping to my PPF installer on the outskirts of town. There is literally no way to drive the car in 6th gear and keep to within 10 miles of legal speeds without the cabin being filled with a BOOOMING drone.

I'll be keeping an ear out for this on our holiday trip up to the Carolina mountains. The car only has ~500 miles right now. Maybe I should do some before and after measures between now and the break-in service?

Metak, if you need me to take any decible measurements let me know. I'll have to find an app to do it but I've seen a couple on the App Store.

[mikewills]

Originally Posted by b33g33

Seconded.

I noticed this the most while schlepping to my PPF installer on the outskirts of town. There is literally no way to drive the car in 6th gear and keep to within 10 miles of legal speeds without the cabin being filled with a BOOOMING drone.

I'll be keeping an ear out for this on our holiday trip up to the Carolina mountains. The car only has ~500 miles right now. Maybe I should do some before and after measures between now and the break-in service?

Metak, if you need me to take any decible measurements let me know. I'll have to find an app to do it but I've seen a couple on the App Store.

I have the SPL meter at the below link that I used to calibrate my Home Theater. Let me know if you need help with the measurements.

http://www.tnt-audio.com/clinica/spl-meter_e.html

[Mr.Metak2you]

Originally Posted by superchargedman

We already have a long thread on the controversy of this "drone."

There really shouldn't be any controversy. There IS a drone on the OEM system. This thread is different because it is seeking a possible solutions for those interested. Anyone not interested can just move along....This thread is not intended to continue a debate of whether or not there is a drone or not, anyone who does so is taking the thread OFF TOPIC.

[sparoz]

iPhone spl is around 84db at drone range. I found there are certain days worse than the others.

So far the feedback from the Akra exhaust is there is no drone at the dreaded range.

[Mr.Metak2you]

FOR EXAMPLE:

Base reference velocity is 1128 ft/sec @ 20 C or 68 F.

The Math:

Frequency (f) = Velocity of Sound (V) / WaveLength (Lw)

assume a working resonator temp of ~50 degrees C (122 F):
V is 1187 Ft/sec.

125Hz = 1187 / Lw, or, Lw = 1187 / 129 = 9.2 feet.

The resonator is a quarter-wave resonator, so that its length must be 9.2/4 = 2.3 feet or 27.6 inches.

Here is a few before/after idle and 2300RPM wave profiles. Notice the low frequency peak? This is drone. The branch resonator will reduce significantly a narrow frequency range and ONLY that range. Cruise in 6th in peace. Last picture is a Porsche muffler delete(LOUD AS FUCK!) but without drone because of the use of branch resonators. It also looks like there is some x-pipe principle being used as well. So regardless of what you use, H-pipe, J-pipe, branch, whatever, this is nothing new. Hot rod muscle cars have been using this to avoid drone.

X-OST Maranello(an Italian Ferrari aftermarket) states on their website: "X-OST Maranello hand assemble the finest aftermarket exhaust systems available today for your Ferrari. Fitting all current Ferrari models, X-OST Maranello also has applications for virtually all Ferraris' going back to the early 12 cylinder classics of the sixties and everything in between. Special attention is given to the elimination of drone which many other aftermarket mufflers suffer from." They certainly didn't tell their customers, "there is no such thing as drone" and "go buy a Prius", or "get some earplugs", "turn up your stereo" etc....

DINAN(http://www.dinancars.com/webresource...92Exhaust3.gif) and AA(http://cdn.nexternal.com/aaw/images/Large5.jpg) have developed exhaust systems for the E9x M3 and both implement some sort of closed end resonance absorber to avoid drone while increasing performance and sound!

[Mr.Metak2you]

My neighbor has a garage full of muscle cars and plan to use his knowledge on the subject. He has a G8 as a daily driver(it's a beast) and he directed me to this website that has adjustable closed end J-pipe resonators that are tunable(4") being used on his car. Tunable meaning you can make the adjustment to whatever length is necessary so you can tune out the frequency(Hz) at the specific cruising RPM speed that has the bothersome drone.

http://www.g8board.com/forums/showthread.php?t=28454

[oldBMWguy]

Mr. Metak--- What you are saying re all that Res. frequency makes some sense, but I am just a plain old civil engineer-- anything more that roads, buildings, good water, and bad crap is beyond me....... but are you saying we just need to cut a hole [or two?] in the exhaust pipe and weld one or two 27 in. closed end pipes into them, and find the space to fit them............ and the drone will be reduced/gone ??

[1SerieStud]

Originally Posted by oldBMWguy

Mr. Metak--- What you are saying re all that Res. frequency makes some sense, but I am just a plain old civil engineer-- anything more that roads, buildings, good water, and bad crap is beyond me....... but are you saying we just need to cut a hole [or two?] in the exhaust pipe and weld one or two 27 in. closed end pipes into them, and find the space to fit them............ and the drone will be reduced/gone ??

Something is way off with the calculations - I haven't looked into it myself though since I like the exhaust just the way it is.

The S2000's oem exhaust system mimics something similar to what is being described here and the perpendicular tubing is no longer than 6-8 inches long. Granted, different piping diameter, different engines, etc, but good luck trying to find space for 27'' of piping.

Also, the diameter of the piece of tubing will also influence the outcome of this experiment. So maybe it does not have to be that long if the diameter is changed. Again, not something I want to put any effort into, but just throwing it out there.

[1M Fan]

So, would an X or H pipe help if it is installed in front of the secondary cats? I haven't looked up there, but it can't be that hard to install or cost too much.

[Mr.Metak2you]

Originally Posted by oldBMWguy

Mr. Metak--- What you are saying re all that Res. frequency makes some sense, but I am just a plain old civil engineer-- anything more that roads, buildings, good water, and bad crap is beyond me....... but are you saying we just need to cut a hole [or two?] in the exhaust pipe and weld one or two 27 in. closed end pipes into them, and find the space to fit them............ and the drone will be reduced/gone ??

The "example" calculation is from a Porsche forum my friend/coworker is on. You would only need one tubing at that length or two at 1/2 length each(~12"). But if you use a U or J bend the length may only be 8" or so with a 3.75" center line radius bend. The bend will actually help cancel the frequency. I already have an Eisenmann Sport exhaust on order so this is just an exercise to see if it can be done. We just have to get a good recording of the drone. I can analyze the profile in my Cakewalk, Sonar or even CoolEdit95. Then whatever frequency it is, the equation will give us the length needed, which will probably be less that 27" because we are not doing a muffler delete or anything. Make sense?

Originally Posted by 1M Fan

So, would an X or H pipe help if it is installed in front of the secondary cats? I haven't looked up there, but it can't be that hard to install or cost too much.

Definitely, but I don't know of any that are available and would cost a lot more. You can buy a mandrel bent 304 SS tubing for $30-$40.

Originally Posted by 1SerieStud

Something is way off with the calculations - I haven't looked into it myself though since I like the exhaust just the way it is........ Again, not something I want to put any effort into, but just throwing it out there.

In that case you can keep your useless posts to yourself.

[Mr.Metak2you]

Originally Posted by mikewills

I have the SPL meter at the below link that I used to calibrate my Home Theater. Let me know if you need help with the measurements.

http://www.tnt-audio.com/clinica/spl-meter_e.html

You know Mike, I missed your post/link. I think if your SLP Meter can measure the "peak" not average frequency(Hz) in the C-weighted(full range mode) at ~2300RPM(I think that where the drone is most prevalent) that would be awesome!

[johnsfb]

Originally Posted by Mr.Metak2you

There really shouldn't be any controversy. There IS a drone on the OEM system. This thread is different because it is seeking a possible solutions for those interested. Anyone not interested can just move along....This thread is not intended to continue a debate of whether or not there is a drone or not, anyone who does so is taking the thread OFF TOPIC.

What about something like this (on a 135i) maybe. OK, so the system is different but I mean the idea of the dead-end stub pipe.

[Mr.Metak2you]

Originally Posted by johnsfb

Something like this (on a 135i) maybe. Not the system --- just the idea of the dead-end stub.

Exactly. Without that resonator that thing would melt your brain with the drone. Looks good and I best it sounds ridiculous! Any sound clips?