As you may already know, the majority of in-ear headphones come with dynamic drivers to generate sound. The main reasons being, they are relatively cheap to manufacture and cover a wide frequency range. However, the makers of the Delta, UK-based Trinity Audio Engineering, have opted for a hybrid system for delivering high quality sound.
Not only have they used a dynamic driver, but also incorporated a Balanced Armature (BA) into their design.
Without getting too technical, BA’s are typically used in high-end gear like professional in-ear monitors. The advantage of using a BA is they can be very accurately tuned to specific frequency bands. This gives more precise audio detail, especially in the mid to highs.