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      10-19-2011, 09:46 PM   #133
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What were to conditions that you posted that there was no drone at all? How could the drone come back after the "overkill" was put in, maybe you were not driving it on load (note: it will only drone on load).
In my car it comes and goes. I can nudge the gas a little and it will go away. It will stay away and then come back. Other times, It is always there and sometimes in never happens. It is very inconsistent. Every test drive is at least 20 miles to warm it up, then see if it will drone or not.
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      10-20-2011, 06:45 PM   #134
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In my car it comes and goes. I can nudge the gas a little and it will go away. It will stay away and then come back. Other times, It is always there and sometimes in never happens. It is very inconsistent. Every test drive is at least 20 miles to warm it up, then see if it will drone or not.
Wow! I would see that your dealer would be able to help with that as it is on/off.

Mine I just on all the time.
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      10-20-2011, 06:54 PM   #135
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I was picking up the new X3 yesterday and the old Service Manager was back helping out as one of their staff is away (he was promoted ). Had a chat to him and he's going to test drove with me. He said as it is in every gear in the same rev range at the same load, it is more than likely to be the exhaust. He is going to loosen everything up, run the car and re tighten everything to see if it solves the problem as that often does. I will keep you guys posted.
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      10-25-2011, 09:46 AM   #136
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Any new ideas, thoughts, comments on how to reduce "drone"?
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      10-25-2011, 11:31 AM   #137
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So, for those of you who did the insulation in the trunk, did it also deaden the normal "nice" sound in the other gears? Or did it selectively delete the higher-gear drone issue? I was just wondering this morning if the nice tone we hear going through the gears will be muffled away with that fix.
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      10-25-2011, 08:05 PM   #138
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Quote:
Originally Posted by T1T2GRE View Post
So, for those of you who did the insulation in the trunk, did it also deaden the normal "nice" sound in the other gears? Or did it selectively delete the higher-gear drone issue? I was just wondering this morning if the nice tone we hear going through the gears will be muffled away with that fix.
The drone is simple resonance, that is frequency matching caused by natural vibrations of the engine, exhause gas and exhaust pipes. I submit that a simple change in the diameter of the piping, more or less, will eliminate the drone. Aircraft designers, bridge builders and any other structure is always designed with resonance in mind. Eventually it will damage or destroy the integrity of the material to which it impacts. Tightening the pipes will not help, wrapping them will only hide or surpress the noise, in order to make it go away the actual resonance needs to be cancelled. Think about two waves joining in sync... they get bigger. Now those two same waves can also cancel each other out. That is what you want. So... the natural vibration frequency of the engine at the point you hear the drone, just happens to match that of the exhaust piping. You would have thought the M team would have considered normal cruising RPM and adjusted the piping size accordingly.
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      10-25-2011, 08:08 PM   #139
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Quote:
Originally Posted by Rekraps View Post
The drone is simple resonance, that is frequency matching caused by natural vibrations of the engine, exhause gas and exhaust pipes. I submit that a simple change in the diameter of the piping, more or less, will eliminate the drone. Aircraft designers, bridge builders and any other structure is always designed with resonance in mind. Eventually it will damage or destroy the integrity of the material to which it impacts. Tightening the pipes will not help, wrapping them will only hide or surpress the noise, in order to make it go away the actual resonance needs to be cancelled. Think about two waves joining in sync... they get bigger. Now those two same waves can also cancel each other out. That is what you want. So... the natural vibration frequency of the engine at the point you hear the drone, just happens to match that of the exhaust piping. You would have thought the M team would have considered normal cruising RPM and adjusted the piping size accordingly.
Nope. Changing the diameter of the pipe will simply move the resonance frequency.
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      10-26-2011, 09:21 AM   #140
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Quote:
Originally Posted by Rekraps View Post
The drone is simple resonance, that is frequency matching caused by natural vibrations of the engine, exhause gas and exhaust pipes. I submit that a simple change in the diameter of the piping, more or less, will eliminate the drone. Aircraft designers, bridge builders and any other structure is always designed with resonance in mind. Eventually it will damage or destroy the integrity of the material to which it impacts. Tightening the pipes will not help, wrapping them will only hide or surpress the noise, in order to make it go away the actual resonance needs to be cancelled. Think about two waves joining in sync... they get bigger. Now those two same waves can also cancel each other out. That is what you want. So... the natural vibration frequency of the engine at the point you hear the drone, just happens to match that of the exhaust piping. You would have thought the M team would have considered normal cruising RPM and adjusted the piping size accordingly.
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Nope. Changing the diameter of the pipe will simply move the resonance frequency.
I would think that's what he meant by eliminate - eliminate from cruising speed.

Unfortunately, they probably only have Germany's cruising speed in mind where there is no drone.
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      10-26-2011, 09:50 AM   #141
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Reducing drone go get a 128i

I can hear what you guys are saying but its an ///M would you rather it be quiet SMH.
I Cant wait for an exhaust on mine
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      10-26-2011, 11:17 AM   #142
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Exclamation Hopefully DINAN has a solution in the works!

I posted this in the 'Drone Poll' thread and I thought I would added it here, hope this gives some insight to the designing/developing approach to drone:


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I think maybe this should have been established page1.

But DRONE is:

A continuous, low frequency, monotonous sound.

It doesn't even need to be loud, in fact it is usually under very light load in lower RPM's. Just read what DINAN engineers struggled with on the E9x M3 exhaust they were developing. They state: "We worked at designs that would maintain the dual exhaust outlets but each iteration resulted in a heavy, low frequency drone with far too much back-pressure to produce any substantial power gains." Yet some M3 owners scoffed at the DINAN exhaust because the outer pipes were faux. For me and many others who bought the DINAN exhaust, the real functional gains and the lack of drone was more important.

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      10-26-2011, 12:29 PM   #143
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So we know what to work with, here ...
Quote:
Originally Posted by Rekraps View Post
The drone is simple resonance, that is frequency matching caused by natural vibrations of the engine, exhause gas and exhaust pipes.
Vibrations together with their environment. In free air vibration dissipates immediately in all directions, without restriction, whereas in other situations vibration is amplified by any nearby or attached hardware, especially enclosure(s).

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I submit that a simple change in the diameter of the piping, more or less, will eliminate the drone.
Not necessarily. It would merely alter it.

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Originally Posted by Rekraps View Post
Eventually it will damage or destroy the integrity of the material to which it impacts.
Only in extreme sympathetic (harmonic) situations.

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Originally Posted by Rekraps View Post
Tightening the pipes will not help, wrapping them will only hide or surpress the noise.
No. Damping/wrapping reduces amplitude, which results in reduced audibility. To the extent that the vibration is absorbed by the damping material and becomes heat, it is eliminated as noise.
By itself tightening the pipes might help, BTW, if it reduces amplitude (through making it more difficult for the materials to vibrate).

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In order to make it go away the actual resonance needs to be cancelled.
Not necessarily. Damping and/or other control is the most efficient technique.

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Originally Posted by Rekraps View Post
... cancel each other out. ... You would have thought the M team would have considered normal cruising RPM and adjusted the piping size accordingly.
To "cancel" vibration there would have to be a second vibration/resonance of the same frequency(s) and the same amplitude generated and then added exactly 180 degrees out of phase (by some additional hardware) in order to cancel the original resonance. Pretty costly and impractical.
Changing the size/materials/mounting/etc. is what controls the frequency of the resonance ("pitch") and amplitude ("volume").

TMI here, for sure.
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      10-26-2011, 05:22 PM   #144
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Quote:
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Reducing drone go get a 128i

I can hear what you guys are saying but its an ///M would you rather it be quiet SMH.
I Cant wait for an exhaust on mine
I rather it be louder. I also rather it had no drone.
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      10-31-2011, 09:45 AM   #145
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new exhaust

The drone completely gone.

I’ve had my new exhaust on the car for a while now and it has settled in and sounding a bit deeper than at first.

Maybe the best way to describe it is that it works the same way as the Akrapovic BMW X5M (mine is similar to the picture on their website) and probably the same as their 1M although I haven’t yet seen a picture of that.

The difference in mine is that the valves are actuated by the turbo boost and not electronically. This means that when you put your foot down a bit the valves open and the exhaust flow by-passes the back box and exits straight out through the outer two tips and the noise is brilliant. Normally the flow goes through the rear box and actually is slightly quieter than standard but certainly deeper with wuffles and pops.
The other difference in the system is the two secondary cats have been taken out and the centre silencer replaced by one slightly larger. Instead of a single pipe exit from this new centre box there’s now two pipes back to the rear. They said the size of this box is optional according to what noise levels you’re looking for.
This was made by BCS Automotive who are based in St Helens and the four hour drive down there from Perth was certainly worthwhile. They've got a video www.bcsautomotive.co.uk

My insurance people said ok and no extra premium and that was a surprise.
Dealer knows and not bothered.

So, relatively quiet when I want or WTF if I feel like it.
All this and no drone - happy me. Great outcome.

Last edited by johnsfb; 11-01-2011 at 05:13 AM.
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      10-31-2011, 07:31 PM   #146
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I emailed BCS automotive but never got a response.
There is nothing to suggest their products are available in the US.
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      12-01-2011, 09:28 AM   #147
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BCS automotive will sell direct to US customers at a very good price for now. Set up includes throttle controlled valve.
Eager to try out. Also they are testing with a GIAC engine tune.
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