JBL Pro Sound is achieved through robust 40mm Mica Dome drivers, which are precisely tuned to deliver deep bass, balanced mids and crystal-clear highs. Each Mica Dome deliver refined high frequencies above 40kHz for the best on-the-go listening experience. Mica is a renewable mineral that can be split into extremely thin elastic plates, making it flexible enough to respond fast and precisely to the electrical signals in headphone drivers.