The Professional resonator cups for your car.
A pic of my humble chariot!
The final installed position in the car, with a little help from Blu Tack! Also note cup surface direction, see the 4 little wings, the smallest surface in between the wings face front towards wind shield.
I took this from another review of the resonator cups inside some body's car. It could work this way too! Try it out.
I put up my car audio system in the article, so that you know, I ain't talking about the plain Jane OEM stuff. It's a serious enthusiast system.