The most popular of the Etymotic Research flat response attenuators, the ER-15 is recommended as the first choice for hearing protection for musicians, whether they perform in the symphony or local rock band or they teach music at school. Designed for use with the Westone's DefendEar Concert (Style 49) Musicians' Earplugs. Etymotic filters feature a flat frequency response that allows musicians to hear their performance accurately while providing hearing protection. The ER-15 provides a uniform flat 15 dB of sound reduction from 125 Hz through 8 kHz.