Strong air vibration in cabin - Chevy Bolt EV Forum
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post #1 of 7 (permalink) Old 06-26-2019, 12:45 AM Thread Starter
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Strong air vibration in cabin

If I open either (or both) rear windows at normal highway speeds, there is a loud vibration/oscillation (about 5-10 times per second) of the air inside the cabin. It's similar in nature to 'water hammer' in plumbing, but never stops. It's so loud it hurts my ears.
Opening a front window reduces the vibration. I figure it's some sort of aerodynamic issue. For the technically inclined, I would describe this as a relaxation oscillation.
Has anybody else experienced this? It's not subtle.
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post #2 of 7 (permalink) Old 06-26-2019, 07:26 AM
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Commonplace on modern vehicles, it's a side effect of low drag aerodynamics. I know for the Volt there were/are kits that modify the side mirror housings to reduce the "thrum".

Presumption on the automakers part these days is nobody drives with the windows down. I don't, it's too hot, too cold, raining, or there's too much pollen in the air.

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post #3 of 7 (permalink) Old 06-26-2019, 09:53 AM
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What you are experiencing is normal. A front and back window needs to be open in order to eliminate the vibration. Experiment until you find the best opening for both.
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post #4 of 7 (permalink) Old 06-26-2019, 10:22 AM
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p. 52 of my 2017 owners manual:
Quote:
The vehicle aerodynamics are designed to improve electric range performance. This may result in a pulsing sound when either rear window is down and the front windows are up. To reduce the sound, open a front window.
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post #5 of 7 (permalink) Old 06-26-2019, 12:38 PM
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These articles can say it better than I:
https://jalopnik.com/why-do-slightly...oun-1447498738
https://www.caranddriver.com/news/a1...ne-car-window/

We had a car that had a setting for the sunroof that would open it about 75% because if you opened it 100% with the windows up you would get that resonance.

PS: Cracking a front window a few inches usually helps a lot.
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post #6 of 7 (permalink) Old 06-26-2019, 12:41 PM
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Originally Posted by eye diagram View Post
If I open either (or both) rear windows at normal highway speeds, there is a loud vibration/oscillation (about 5-10 times per second) of the air inside the cabin. It's similar in nature to 'water hammer' in plumbing, but never stops. It's so loud it hurts my ears.
Opening a front window reduces the vibration. I figure it's some sort of aerodynamic issue. For the technically inclined, I would describe this as a relaxation oscillation.
Has anybody else experienced this? It's not subtle.

Every car I've ever driven does this. I used it as an "independent experiment" for my high-school physics classes. Then I'd have them write up an explanation for why cars do this, and relate/explain the frequency of oscillation to the sounds made by both a flute and piccolo. (Flutes and piccolos operate by similar principles.)

I "fixed" the problem by opening the front passenger's side window and rear driver's side window each about 4cm. It allows air to flow through, without oscillation (or mussing up the hair).

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post #7 of 7 (permalink) Old 06-26-2019, 12:56 PM
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If you open a front and rear window an equal amount that's usually sufficient to prevent or stop the oscillations. Unequal openings between front and rear windows will start/increase oscillations.

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