The ER4 series, made up of the ER4S, ER4P and ER4B have been Etymotic's top-of-the-line canal phone series since their introduction in 1991. The ER4P are specifically targeted towards more mobile and/or value-oriented consumers, with their enhanced bass response without the need for cumbersome and often expensive amplification. Utilizing rubber triflange or foam tips the ER4 series are designed for outside noise reduction, and audiophile level sound quality. A good pick for those who desire high quality sound reproduction, yet also travel often or simply wish to listen without the discomfort and risk of listening at high volume levels.