Howard Leight Shooter's Premium Earmuff Leightning L3
Because of all the noisemakers I've assembled, I saw fit to invest in a pair of earmuffs.
These are non-electronic shooter's muffs, with a noise reduction rating (NRR) of 30dB. They're adjustable and comfortable, and they do a good job of muffling noises.
If you're going to be messing around with noise, muffs are a very good idea.