Re: 98 Passat Wagon - Helicopter mode

[Don Hoefer <hoefer@eng.pko.dec.com>]

John,

> Has anyone else discovered the problem with the new Passat
> Wagon's design?  If you have the sunroof open all the way
> with the windows closed, and drive anywhere near 50MPH,
> the air pressure pulses rapidly popping your ears HARD and
> it sounds like a helicopter.
> 
> Do any of the Audi's have this problem?

Oh yes.  Think of an organ pipe.  A long tube with a hole in it.
It will resonate at it's natural frequency.  The bigger the pipe
the lower the frequency.  Cars are pretty big.  My Coupe must do
three or four hertz.  To stop the pipe from vibrating, drill a hole
in it to set up canceling resonances, or open a window in the car.

Don Hoefer
'82 Coupe

Massachusetts, USA