Various implementations include headphone systems. In one implementation, a headphone system includes: a pair of earcups; a continuous headband spring connecting the pair of earcups, the continuous headband spring having an internal slot with an opening along an inner surface thereof; and an adjustment apparatus coupled with one of the pair of earcups and the continuous headband spring, the adjustment apparatus having: a shoe coupled with the one of the pair of earcups and positioned in the internal slot; a tongue coupled with the shoe and extending at least partially along the continuous headband spring; and a resistance member coupled with the tongue for resisting movement of the tongue relative to the continuous headband spring.