Westone has never stated anything specific except once on Facebook they said UM30 was to be "more refined". I emailed one of the engineers at Westone today for,yet, another clarification. The UM30 seems less "closed in" than UM3X to me. Maybe "star" tips providing more air or my mind playing games with me. But I also had star tips with UM3X towards the end and didn't notice. If Westone replies I will pass on.