For more than a couple of decades, Etymotic Research’s ER-4S is counted as one of the most precise high-fidelity, noise-isolating earphones. Due to this and its 30-40 dB noise isolation, the ER-4S has not been changed from a long time. Etymotic Research has proclaimed an upgrade to two different models of its classic ER-4 insert earphones, first is the new ER4SR Studio Reference earphone and the other is the ER4XR Extended Response model. Great Functionality The new Etymotic ER4SR (‘Studio Reference’) in-ear headphones are composed armature single-driver designs in which the Etymotic states are more unified and coherent than multiple-driver arrays. The Etymotic ER4SR earphone is devised for demanding audio professionals and audiophiles wanting greater neutral transparency. It improves the already outstanding tonal accuracy of the preceding ER-4S model and provides better sensitivity specs in order to make it more compatible with latest portable media players. Quality Design Planned and manufactured by the engineers of the USA, the Etymotic ER4SR is a freshly updated in-ear headphone. It comes with anodized metal housings, precision-machined, and the identical Etymotic industry-leading 1dB match among left and right channels thru all audible frequencies. Individual channel-matching performance chart is provided with this pair of new Ety ER4-series earphones.