Texas has this thing. They make road surfaces out of chipseal. Chipseal is a really coarse form of asphalt that makes a really rough surface. Generally, chipseal is suitable for 45mph backroads, but Texas puts it on 70mph highways. (Practically every backroad in Texas is a 70mph highway.) It's a really loud surface to drive on.
Along comes the Mazda3.
I've had it for quite a while now. It's a 2013. It rides like a roller skate. I really like that. It's still like new; it's only got 25,000 miles on it. I have to gas it up once or twice a month and it only takes 9 gallons. There is a lot to like about that car. Except the road noise.
It's loud. It's loud on normal roads, but unbearably loud on Texas high-speed chipseal roads. The noise comes from the tires. I researched and bought the quietest tires I could get for it. I bought new tires before the original ones were even worn out. That helped, but not enough. I downloaded a sound meter app to my phone. Normal comfortable background noise is 70 decibels. The Mazda, on the loudest chipseal is 80 decibels. I took it to an auto stereo installer. I asked if they did any soundproofing on cars before they installed expensive stereo systems. They said they did. I asked if they could pretend they were going to install an expensive stereo system in my car, but stop when they finished the soundproofing. They said they would.
Soundproofing involves sticky patches of thin sound insulation stuck out of sight to inside surfaces in the car. They took off the door panels and soundproofed the skin of the doors. They took out the seats, lifted all the carpeting, and soundproofed the floor, firewall, and inside the wheel wells. It is soo much quieter now. On a normal stretch of road it's a nice quiet 60 decibels. I can listen to the radio without having to turn it up past my pain threshold. On the loudest stretch of pavement, instead of measuring 80 decibels, which is in the danger zone for hearing damage if that level is maintained for too long, it measures 75. That's doesn't sound like as big a decrease as I expected or had hoped for, but we have to consider that decibels are a progressive scale. 80 decibels is twice as loud as 70 decibels. By dropping to 75 decibels, we've accomplished a 25% reduction of total sound on the noisiest road possible. Most of the time I'm not on that road. I can now cruise normal highways at a very comfortable 60 decibels, which is only half the noise level of an acceptable 70 decibels.
Brilliant!