View Poll Results: Have you experienced helicopter like sounds when rear windows rolled down?
Yes, it's extremely annoying!
20
74.07%
Yes, slightly but it's acceptable.
4
14.81%
No, the cabin is nice and quiet.
3
11.11%
Voters: 27. You may not vote on this poll
Helicopter Noise When Rear Windows Down
10-31-06, 09:07 AM
#1
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Helicopter Noise When Rear Windows Down
Has anyone else noticed a helicopter like noise when one or both rear windows are partially down?
I live in the LA/Orange County area of California and it's not too uncommon hearing traffic choppers flying around. The first time I noticed this, I thought that a helicopter was about to land somewhere nearby. Then I realized it was caused when the rear windows are rolled down.
It occurs when traveling around 30 - 45 mph when I noticed the extremely annoying thumping sound.
I live in the LA/Orange County area of California and it's not too uncommon hearing traffic choppers flying around. The first time I noticed this, I thought that a helicopter was about to land somewhere nearby. Then I realized it was caused when the rear windows are rolled down.
It occurs when traveling around 30 - 45 mph when I noticed the extremely annoying thumping sound.
10-31-06, 09:22 AM
#2
MultiTasking Mom
the helicopter noise is a physics thing, not a car thing. the flow of air when you have your rear windows down is such that the air cannot escape smoothly so that you get the thumping. every car i've ever had does it.
there are two ways to eliminate this:
(1) don't roll down your rear windows (i mean only your rear windows) while traveling at high speeds
(2) crack your sunroof or one of your front windows just a touch - that will dramatically change the air flow and eliminate the thumping noise
there are two ways to eliminate this:
(1) don't roll down your rear windows (i mean only your rear windows) while traveling at high speeds
(2) crack your sunroof or one of your front windows just a touch - that will dramatically change the air flow and eliminate the thumping noise
10-31-06, 09:30 AM
#3
Moderator
It has to do with standing waves/hamonic frequency in a chamber.
If it was not for this, we would never have the sweet sound of instruments like flute etc.
RX300 has this for sure and it can be painfully annoying.
Later models have a different cabin (slanted rear door) and that could have made some difference. The cabins are still fairly air tight, so I assume the frequency would have shifted.
Since this sub-forum excludes 300 models, let see what ppl have to say.
Salim
If it was not for this, we would never have the sweet sound of instruments like flute etc.
RX300 has this for sure and it can be painfully annoying.
Later models have a different cabin (slanted rear door) and that could have made some difference. The cabins are still fairly air tight, so I assume the frequency would have shifted.
Since this sub-forum excludes 300 models, let see what ppl have to say.
Salim
10-31-06, 09:37 AM
#5
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I've never experienced this type of sound with any other vehicle at the level of intensity with the RX either car or SUV. I don't disagree that this noise occurs to a certain degree with all cars. However, I would argue physics is part of car design....aerodynamics. If a manufacturer found wind affected some feature adversely, or introduced an unwanted result, changes are made.
In this case, I'm wondering if this issue affects all RX's or if it's isolated to a few instances like mine.
In this case, I'm wondering if this issue affects all RX's or if it's isolated to a few instances like mine.
10-31-06, 10:32 AM
#6
MultiTasking Mom
I've never experienced this type of sound with any other vehicle at the level of intensity with the RX either car or SUV. I don't disagree that this noise occurs to a certain degree with all cars. However, I would argue physics is part of car design....aerodynamics. If a manufacturer found wind affected some feature adversely, or introduced an unwanted result, changes are made.
In this case, I'm wondering if this issue affects all RX's or if it's isolated to a few instances like mine.
In this case, I'm wondering if this issue affects all RX's or if it's isolated to a few instances like mine.
i agree there should be a way to design a car in such a manner to limit the effect, but i've never been in a car that doesn't do it so i'm not sure. my sister is a german car lover, and all her previous benzes and current bmw x5 do it also...
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10-31-06, 10:55 AM
#8
I have the same issue. IF you do a search in the RX330 forum you will find when this car was brand new back in 2003 many of us discussed this before. It really is annoying for those that roll the window down. Fortunately for me I like to use the AC all the time so I keep the windows up. I always notice it when I have my dog in the car since at lower speeds he likes to stick his head out the window.
10-31-06, 12:42 PM
#11
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If you want to get geeky, HERE's the explanation of the phenomenon evidently called Helmholtz Resonance. HERE's the Wikipedia explanation.
Yes, it happens on most vehicles, but I think the low frequency produced by the RX and similar vehicles is what makes it so annoying. In the other thread, someone mentioned they not only heard the thumping helicopter, but also felt it. I assume this is because of the low frequency that makes it similar to a bass effect from a sound system.
Yes, it happens on most vehicles, but I think the low frequency produced by the RX and similar vehicles is what makes it so annoying. In the other thread, someone mentioned they not only heard the thumping helicopter, but also felt it. I assume this is because of the low frequency that makes it similar to a bass effect from a sound system.
10-31-06, 01:25 PM
#12
Out of Warranty
If your moonroof has been properly initialized (see manual), you'll notice that using the one-touch feature, it slides back about an inch or so short of full opening. If you press the switch again, it should open all the way. That first "stop" is designed to minimize the cabin resonance at speed.
Your RX resonates like a very large flute. Air passing over an opening will tend to make a sealed chamber resonate (see Helmholtz Resonance above). If you've blown over the top of a bottle, you know that with a little practice you can produce a whistle. That's what's happening here. You have three choices to eliminate or reduce the resonance:
More at: https://www.clublexus.com/forums/rx-1st-gen-1999-2003/74951-how-do-i-fix-the-window-cavitation-problem.html
Your RX resonates like a very large flute. Air passing over an opening will tend to make a sealed chamber resonate (see Helmholtz Resonance above). If you've blown over the top of a bottle, you know that with a little practice you can produce a whistle. That's what's happening here. You have three choices to eliminate or reduce the resonance:
- Unseal the chamber - crack one or more windows. Most cars do not produce this effect because the cabin is not often as tightly sealed as the Lexus'.
- Change the opening in the chamber - open or close the offending opening slightly to change the airflow over it.
- Change the free air capacity of the cavity - carry four large friends or a medium sized mattress with you at all times.
More at: https://www.clublexus.com/forums/rx-1st-gen-1999-2003/74951-how-do-i-fix-the-window-cavitation-problem.html
10-31-06, 02:09 PM
#15
Moderator
TripleDes:
You have cracked open the Pandora's box yet again.
Salim
You have cracked open the Pandora's box yet again.
Salim