This thread is for impressions and reviews of the Stealthsonics U-series and C-series IEMs. Impressions links: https://audioprimate.blog/2018/10/19/stealthsonics-u4-and-u9-unboxing-and-initial-impressions/ Full review links: [U4] https://www.head-fi.org/showcase/review/22212/ [U9] https://www.head-fi.org/showcase/stealth-sonics-u9.23772/reviews#review-22211 [More to be added] The models: The specs: The Technology: Iso-Stealth Technology: Audiology in Action Through our advanced audiology research, testing and international network of over 700 audiology partners, we’re able to go beyond our competitors to engineer ultra-precise, second-bend ear canal impressions to position our IEM within just millimeters of the eardrum. Wearers can listen at safer SPLs for a cleaner mix, with less ear-cavity interference and a consistent sonic experience every time. SonicFlo Acoustics: The Aerospace Advantage We’ve harnessed our technology breakthroughs in the aerospace industry to optimize aerodynamics, aeroacoustics and airflow performance. We’ve also taken advantage of our extensive research in fluid dynamics principles to engineer our in-ear monitors for optimum sound isolation in any environment. Acoustic Optimization: From Drivers to Damping Acoustic refinements include extra-large bores that preserve airflow and sonic fidelity and advanced venting features to manage resonance. All of our universal in-ear monitors offer Stealth Damping technology , featuring a faceplate that can be removed to extend bass response for deep, rich low end that you can feel. Space-Age Materials: Comfort and Confidence Components are built inside an ultra-light enclosure housed in proprietary composite material that ensures a snug, comfortable, slip-free fit, even during long-term use. Klarity Valve, Hearing Protection (custom only?) The Klarity Valve is designed to release pressure build up in the ears arising from long use of IEMs. Without such a 1 way valve, the listener becomes exposed to pressure build up in the ears causing fatigue and hearing stress . Ultra Hard Impact Shells Breakage Resistant Designed to withstand pressures arising for accidentally dropping the IEMs and other typical accidents, the shells are coated with a proprietary lacquer that makes the shells extra hard.