senn記聲稱660s個driver係新設計
Hm. Well they sort of state that it's a new design, but I'm betting that's a bit of poetic license—the HD 700 is a relatively new design. Thing is, impedance and phase measurements are almost identical.
https://www.innerfidelity.com/content/sennheiser-hd-660-s-over-ear-open-headphones