Adorama offers the Astell&Kern Beyerdynamic AK T1p Special Edition Semi-Open Over-Ear Headphones for $524.99 with free shipping. That's $25 below our June mention and the lowest price we've seen. (It's the best deal now by $275, although some retailers charge $1,199.) They feature Tesla drivers, 5Hz to 50kHz frequency response, and 32-ohms impedance. It includes 2.5mm and 3.5mm cables and a 3.5mm to 6.3mm adapter.