Etymotic Research—inventor of noise-isolating in-ear earphones—presents the next generation of Etymotic's long-revered flagship earphone, the ER4SR (StudioReference), part of the ER4® reference earphone series. Developed for auditory research and hearing testing, they use balanced–armature receivers, establishing them as the gold standard for high-definition, in-ear earphones, and were the first high-fidelity, noise isolating, in-ear earphones to offer this technology in a consumer platform, so are recognized as the world leader for signal response accuracy by which all other earphones are measured. Made for those who demand nothing less than the highest fidelity, these are reference-standard high-fidelity earphones. They deliver increased accuracy with greater sound output, or sensitivity, and like their predecessor, their channels are matched within an industry-leading 1 dB across frequencies from 100 Hz to 10 kHz. They also incorporate significant cosmetic and functional improvements, from the sleek, anodized, and laser-etched aluminum body, to the reinforced and user-replaceable detachable cable. A total must-have for discerning engineers, audiophiles, and consumers who want the most accurate in-ear earphone available.Etymotic Research Inc ER4SR Includes:ER4SR earphonesDetachable, 5ft cord with 3.5mm gold-plated stereo plug¼" stereo phone adapterAssortment of eartipsFilter removal tool and replacement filtersShirt clipZippered storage casePerformance certificateEtymotic Research Inc ER4SR Features:Reference standardUnsurpassed frequency response accuracy and sound quality — 92%+ response accuracy from 20 Hz – 16 kHzThe only earphones with balanced-armature, precision-matched, custom-tuned driversHighest output sensitivity in its classProfessional quality and reliabilityMetal bodies with anodized finishDetachable cables allow for easy replacement and customizationAn assortment of noise-isolating eartip options to ensure proper seal and comfortCUSTOM•FIT option available (contact your Sales Pro for more details)First earphones to completely seal the ear98% (35 dB - 42 dB) noise isolation —highest of any earphones or headsets on the market todayReduction of outside noise reduces the risk of listening at unsafe levels2-year replacement warrantyUser-replaceable filters protect the balanced-armature drivers from ear waxEtymotic Research Inc ER4SR Specifications:Frequency Response: 20 Hz - 16 kHzTransducers: High performance, balanced-armature micro-driversNoise Isolation: 35 - 42 dBImpedance (@1kHz): 45 Ohms)Sensitivity (@1 kHz) SPL at 0.1v: 98 dBMaximum Output (SPL): 122 dBCable: 5ft, detachableUser Replaceable ACCU-Filters: YesWarranty: 2 YearsCUSTOM•FIT Option: Available (see note below)NOTE:An industry exclusive channel-matching compliance graph signed by the Etymotic engineer who precision-matched and custom-tuned the balanced-armature drivers is included with every pair of ER•4 earphones.Etymotic offers a cost-effective CUSTOM•FIT solution to make your favorite earphones the best they can be with superb comfort, secure fit, and consistent noise isolation. It requires a brief registration process and a visit with an authorized audiologist to have ear impressions made.Please contact your Sales Pro for more information on this option.Due to the personal nature of its usage, this product is non-returnable. Please contact your Sales Pro if you need assistance when choosing. Etymotic Research ER4SR Balanced-Armature In-Ear Earphones.