Here's where you get those cool custom-made earplugs and earphones. Etymotic Research, Inc. - Musicians Earplugs (ER•9, ER•15 & ER•25): "Accurate sound reduction is achieved by combining a patented filter with the specific acoustics of a custom earmold. The combination of the two produces a resonance at approximately 2700 Hz (as in the normal ear) resulting in a smooth, flat attenuation." [permalink]