What is it about the design of more modern cars that driving with the windows (particularly rear ones) down creates an unpleasant booming noise?
Sure, aircon being standard now means we shouldn’t need the windows down, but sometimes I just quite like an open window as I’m cruising along back country roads.
My first car/s sans aircon were fine with the windows down, and also had that little triangular pop-out window in the front seats to ensure a stream of wind in your face on the warmer days.
But any cars I’ve had manufactured later than say 1985 make it impossible to enjoy the ambient freshness (and smells) of the surrounding countryside.
Aerodynamics. Modern cars are designed to operate with maximum fuel efficiency and one of the ways to do that is to make the car as aerodynamic as possible. As it turns out, open windows do a lot to lower the aerodynamic efficiency of a moving car, so they are designed to operate best at highway speeds with the windows closed.
The buffeting (technically Helmholtz resonance) you feel when one or more windows are open at speed is a result of the overall shape of the car. The smooth flow of air is being disrupted by the open window and it sets up all sorts of bad thing, including that buffeting sensation. Older cars didn’t have streamlined aerodynamics so there was plenty of rough air around a moving car. Today’s car have very smooth air around them so any disturbance is more noticeable.
Telemark nailed it. “Thrumming” (the name for the phenomenon) is Helmholtz resonance. it’s basically the same thing as blowing across the mouth of a beer bottle, except the car’s interior is much larger so the resonant frequency is way lower.
If I see a car driving at highway speed with a window that’s open a few inches, it’s invariably an older style Buick or Olds with a matching older style driver. It was just common knowledge that you had to have a window cracked open when driving to avoid gas fumes in the car. It probably wasn’t a problem long ago because 1) they drove slower and 2) no one had high-quality music systems, but having that older-style car shape doesn’t have that buffeting noise either.
In warm weather I much prefer the open air. Driver’s window down, and right side or rears at least cracked as required. Everything down if not too loud. My first generation Scion xB (the box) is the quietest car I have ever driven with all windows down, a real pleasure.
It’s not just modern cars – that staccato booming sound happened in the 1940s. In those days it was lovely to drive at night and hear the sounds of insects, frogs, etc., even into the 60s, but now roads pass through silence.
It gets really obnoxious when you have asymmetric windows open – like the driver’s window and the off-side rear passenger window. That can lead to some strong thrumming.
A kind of related effect is the pulse-jet apparatus. One of the easiest is to take a jam jar and punch two holes in the metal lid. Then solder a short tube to one of the holes. Now put in some rubbing alcohol and light it. The flame will “pulse” vigorously, as air and heat try to go out the two holes, creating interference.
(Pulse jets of this sort of model can be extraordinarily LOUD! Practitioners of this hobby can set up huge monstrous booming roars, truly dangerously loud.)
The VW Beetle was famous for this sound, as the rear windows didn’t open at all. When I bought my 1965 Beetle, I was glad I got the deluxe model that had rear windows that pushed out just a few inches. It solved the booming sound, which was important, since the car had no air conditioning and you had to keep the front windows open in the summer.
My Honda Fit would set up quite a thrum at highway speeds with the driver’s window open. I discovered that if I cracked one of the rear windows a bit, it fixed the problem. Click and Clack addressed this problem with a car, I can’t remember for sure but I think it was a BMW, and discovered that no combination of windows open/closed/cracked would stop the thrum. So you need to experiment with the car and see what works for your model. Then post an instructional video on Youtube.
You also never drove a station wagon with just the tailgate window open; that’d suck exhaust right into the car for sure. Unless another window was open up front. That’d prevent the problem. It’s almost like Korean Fan Death; everyone knew these facts in their very bones.
Remember that 100% of those folks smoked when they were younger. And it was typical to leaving the smoker’s window down a bit. Unless it was cold. Then everyone enjoyed lots of second hand smoke in a confined space.
Yep, Telemark pretty much nailed it. Also, they don’t design the inside of cars to function well with the windows down at high speed. In my Mini, as soon as you rolled the window down, the seatbelt became a bullroarer.
My Mazda3 is just the opposite. Opening a rear window about 30-35 mpg starts the thrumming, but opening the front window at the same time gets rid of it.
Ahh, the good old days. . . . Mom and Dad and me and my three siblings in our blue Ford station wagon, and Mom and Dad both smoking up a storm in the front seat. If it was cold out, the interior of the care would be a thick blue haze.
