GolfGTIforum.co.uk
Model specific boards => Golf mk6 => Topic started by: takuma on 28 March 2011, 21:45
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While you are on the subject of sunroof. Noticed something today, had it open fully (sunroof only - all windows was shut) and when I hit 30Mph and above, a loud shuddering noise happens. When I said loud I mean loud and very irritating to the point where you have to close it. I couldn't continue to drive with the noise it makes especially if it's on a motorway where speed is constantly over 30mph. Googled up on it and apparently it's the norm? Remedies include opening door windows to reduce/cancel the noise, I've been in other cars with sunroofs fully open driving on the motorways and never experienced an such a sound as the one the GTI generates!
Any thoughts? and sorry to hijack the OP.
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No answers but mine does this too, I just open my window a little and it does seem to help. Still love my little hole in the roof tho.
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It hurts my poor old ears as well at times.
I love the sunroof though and would certainly spec one again. The sunroof looks fantastic on a white golf as weel as it breaks up the roof of the car nicely which I feel makes the car look a wee bit more sportier imo.
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I don't have a sunroof on my current car but I would say this shouldn't happen. When you guys open the sunroof, does a deflector pop up on the leading edge? This used to happen on other cars I have owned. It deflects the air travelling over the roof of the car and stops the 'buffeting' on the ears.
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The aerodynamics causing the pressure difference of the air between the outside and the inside of the car.
If the airflow over the roof remains attached, i.e. laminar, then the buffeting noise will be much less. If the airflow is turbulent, noise levels will be enhanced.
This can be explained by complex 'Boundary Layer Theory'.
The buffeting can be quite bad on some cars where not enough attention has been paid to the positioning of the sunroof and to the height and orientation of the wind deflector.
So if the opening is too large, the pressure difference will be greater and the buffeting noise levels will increase.
Reduce the size of the opening by slightly closing the roof or reduce the pressure difference by dropping a window.
Can't be bothered with sunroofs myself.
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I find lowering the two front windows (3 door) greatly reduces the buffeting noise.
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While you are on the subject of sunroof. Noticed something today, had it open fully (sunroof only - all windows was shut) and when I hit 30Mph and above, a loud shuddering noise happens. When I said loud I mean loud and very irritating to the point where you have to close it. I couldn't continue to drive with the noise it makes especially if it's on a motorway where speed is constantly over 30mph. Googled up on it and apparently it's the norm? Remedies include opening door windows to reduce/cancel the noise, I've been in other cars with sunroofs fully open driving on the motorways and never experienced an such a sound as the one the GTI generates!
Any thoughts? and sorry to hijack the OP.
I turn the dial a couple of notches in turn moves the glass forward slightly which makes the shudder disappear. If you want the sunroof fully open put down your window slightly. My last three cars have had sunroofs Mitsubishi - Audi - VW all are the same
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Mk2's have a flap that deflects the air over the sunroof aperture, it comes up when its opened. Thought after solving this they would have applied it to later models?!
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The aerodynamics causing the pressure difference of the air between the outside and the inside of the car.
If the airflow over the roof remains attached, i.e. laminar, then the buffeting noise will be much less. If the airflow is turbulent, noise levels will be enhanced.
This can be explained by complex 'Boundary Layer Theory'.
The buffeting can be quite bad on some cars where not enough attention has been paid to the positioning of the sunroof and to the height and orientation of the wind deflector.
So if the opening is too large, the pressure difference will be greater and the buffeting noise levels will increase.
Reduce the size of the opening by slightly closing the roof or reduce the pressure difference by dropping a window.
Can't be bothered with sunroofs myself.
Helmholtz resonator? An open roof acts like an organ pipe, exciting the acoustic resonance of the interior air volume - I think. Works with side windows too.
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Is there not a speed where the shuddering disappears again? You may have to try this on a private road :wink:
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The aerodynamics causing the pressure difference of the air between the outside and the inside of the car.
If the airflow over the roof remains attached, i.e. laminar, then the buffeting noise will be much less. If the airflow is turbulent, noise levels will be enhanced.
This can be explained by complex 'Boundary Layer Theory'.
The buffeting can be quite bad on some cars where not enough attention has been paid to the positioning of the sunroof and to the height and orientation of the wind deflector.
So if the opening is too large, the pressure difference will be greater and the buffeting noise levels will increase.
Reduce the size of the opening by slightly closing the roof or reduce the pressure difference by dropping a window.
Can't be bothered with sunroofs myself.
Helmholtz resonator? An open roof acts like an organ pipe, exciting the acoustic resonance of the interior air volume - I think. Works with side windows too.
I thought about this too:
frequency of resonance = [c/(2Pi)] x [square root of s/(lv)]
c = speed of sound
s = cross section area of neck (sunroof opening)
l = length of neck
v = volume of car interior
The narrow neck is the sunroof opening and the inert volume is the cavity of the car. This causes an impedence mismatch between the air on the outside and that inside the car due to the narrow neck which is the sunroof.
Changing 's' would affect the freq of resonance. Closing the sunroof a bit will reduce 's' and lower the resonant freq of the system.
The mechanical analogy is the mass/spring system.
With a Helmholtz resonator, the coupling of the air on the outside and the air in the volume is very weak due to the narrow neck. This produces an impedence mismatch. Additionally, the Helmholz resonator is an acoustic filter (Quincke filter) and cannot produce any sound.
In the case of the organ pipe, the coupling of the air inside the pipe and the outside is good. Hence the organ pipe produces sound.
It is an interesting bit of Physics and a variety of theories may be used to explain this phenomenon.