I used ear muffs I bought at Wal Mart that were battery powered... it adjusted to the DB level. They were made for gun ranges - you could turn up the volume and a mic would pick up regular conversations and a speaker in the muffs would relay the speaking. Sudden and loud sounds (such as gunshots and a TF dragster) would cut out the mic and the sound would be muffled. I also used ear buds plugged into a radio to pick up the track announcer. Otherwise your ears hurt when the cars go, or they hurt cause the tracks audio speakers will make you go deaf sometimes.
As for folks with no ear protection... you're a moron, not a tough guy. Absolute moron. (fingers in the ears does count for ear protection, so I'm only talking guys who purposely don't cover their ears). Theres a reason your ears will HURT if you try to listen to a run with no ear protection, its cause your eardrums are rupturing. At that DB level on a TF car, its not noise anymore, it's a pressure wave and it will do damage to your ears.
Additionally, the tough guys who proudly stand behind a TF car taking deep breaths of nitro and use a pair of oakleys as eye protection, and stand with your arms crossed with no ear protection, you're a moron too. Again, theres a reason why crew members are wearing GAS MASKS and expensive ear muffs.
There are some exceptions, I've seen famous crew chiefs warmup the car with no ear protection and no gas masks. But thats cause they are probably already deaf and their lungs shot.
Kids I'd recommend ear muffs too, if you put in earplugs sometimes they don't seal, and a young kid wouldn't know it and they could be damaging their ears without knowing it.