I recently looked into getting some made after hearing from Jesse F. Keeler in an interview that he used custom earplugs that have a flat frequency response. here's a pic:
they just came in today, and I have to say, if you don't know about them, GET SOME! look around town for an audiologist, and they can give you a hearing test, and get some custom ear molds made. I used a Beltone office, and it was pretty great. a little expensive...$75 per ear, but not bad considering you can't buy more hearing if you run out. but about the earplugs! I used to not use them until I played a gig in which my ears were ringing for about 3 days after, then I started (reluctantly) wearing them anytime I turned my amp up (band practice, shows), and just dealt with the high frequency roll off that starts at around 2k...hated it, but I couldn't risk being deaf in 20 years. fast forward to today when they came in: I practiced with my drummer, and with them in, it was literally like I had just turned the volume down on life. there was no frequency cut or muffling that normally comes with foam earplugs. just a solid 15dB reduction in volume. I could stand ear to my cab with my bass feeding back with the amp on 6 (100w all tube Carvin X100B), and not bat an eye. playing and going to shows are going to be SO much better!!! also, the best part is that the filters are interchangeable. you can use 9, 15, or 25dB filters that reduce the sound by just that much. here's some videos that have a little more info and lets you get an idea of how they look up close, and such. if you don't have some, GET SOME!!!! I can't stress this enough!!!
http://www.youtube.com/watch?v=CEUPlIpkE7o
http://www.youtube.com/watch?v=kUk0OUAvbrA

they just came in today, and I have to say, if you don't know about them, GET SOME! look around town for an audiologist, and they can give you a hearing test, and get some custom ear molds made. I used a Beltone office, and it was pretty great. a little expensive...$75 per ear, but not bad considering you can't buy more hearing if you run out. but about the earplugs! I used to not use them until I played a gig in which my ears were ringing for about 3 days after, then I started (reluctantly) wearing them anytime I turned my amp up (band practice, shows), and just dealt with the high frequency roll off that starts at around 2k...hated it, but I couldn't risk being deaf in 20 years. fast forward to today when they came in: I practiced with my drummer, and with them in, it was literally like I had just turned the volume down on life. there was no frequency cut or muffling that normally comes with foam earplugs. just a solid 15dB reduction in volume. I could stand ear to my cab with my bass feeding back with the amp on 6 (100w all tube Carvin X100B), and not bat an eye. playing and going to shows are going to be SO much better!!! also, the best part is that the filters are interchangeable. you can use 9, 15, or 25dB filters that reduce the sound by just that much. here's some videos that have a little more info and lets you get an idea of how they look up close, and such. if you don't have some, GET SOME!!!! I can't stress this enough!!!
http://www.youtube.com/watch?v=CEUPlIpkE7o
http://www.youtube.com/watch?v=kUk0OUAvbrA