I've seen some aspects of headphone acoustics touched on in older threads, but no recent thread nor much discussion lately. So rather than debating what differences DACs, amps, and cables may or may not make at the edges of perception - which can seem like debating how many angels can fit on the head of a pin - perhaps we can discuss something more practical for head-fiers: how do the various parameters in design of headphone acoustics (driver type, driver diameter, driver placement in 3D and angle relative to the ears, frame mass and stiffness, earpad geometry and stiffness and damping, etc.) affect the perceived sound of headphones? For example, I'm thinking about how the bass character of headphones differs, and how headphones need to create a perception of bass power without being able to deliver bass energy to the entire body, as happens with speakers and normal sounds in the environment. It seems to me that headphone kind of need to 'fake it' since they can't create true visceral impact. If a headphone is relatively heavy and tightly coupled to the head (e.g., LCD-3), does bass energy transfer from the heavier headphone mass to the head, in the form of head vibration, help explain why such a headphone would be perceived as having 'weightier' bass?