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Old 05-11-2019, 01:03 PM   #7 (permalink)
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Originally Posted by nemo View Post
I would think the big source of heat would be the windows.
This^^^. One reason many cars now come with a sound-absorbent layer in the windshield laminate, and many luxury cars with laminate side windows.

Xist, panel dampers like you linked to do one thing--lower the resonant frequency of panels to which they are attached (by turning some of the energy of vibration into heat). It doesn't take much of it to dampen a sheet metal panel like a door.

If you hang around car audio forums, you'll find lots of people using mass-loaded vinyl, a heavy material that absorbs sound energy. I've never seen any scientifically-rigorous test on the effectiveness of this for noise reduction in cars.

Of course, MLV is very heavy and expensive, so OEMs don't use it to sound insulate their cars. If you look at notoriously quiet cars like the Lexus LS and other luxury cars, you can start to pick out trends, like:

-Triple door seals. Most cars have an inner and outer door seal; lots of luxury cars and SUVs have a third seal close to the door edges.

2018 Toyota Prius door edge seal

2019 Jaguar XJL door edge seal

2019 Lexus LS500 lower door seal

2019 Lincoln Continental lower door seal

2019 Ford Edge rear door seal

-Noise-reducing wheels. The current Lexus LS has a resonating chamber in three of its available wheel designs to reduce noise.

-Sound-absorbent pads in the cabin. The Gen 4 Prius uses an unbroken layer of urethane foam under the carpet for noise reduction.

-Covers for access holes on inner door panels.

-Strategic placement of sound-absorbent materials.

2012 Lexus LS600h

If you're really serious about reducing noise, I recommend the second chapter of Theory and Applications of Aerodynamics for Ground Vehicles, "Noise and Vehicle Soiling" (T. Yomi Obidi, 2014), pp. 35-50.

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