OLLO Audio is a Slovenian headphone manufacturer that hand-builds studio headphones in a small workshop on the edge of the Alps. The company specializes in dynamic over-ear headphones engineered for mixing, mastering, and recording, with each pair individually calibrated to a flat frequency response and shipped with its own measurement chart.

The lineup centers on two main lines: the open-back X1 mixing headphones, designed for editing, mixing, and mastering work, and the closed-back R1 (and earlier S4R) recording headphones aimed at tracking vocals and instruments. The brand also produces the S4X reference headphones and the S5X immersive model intended for spatial-audio and stereo monitoring workflows. All models are built around a wood ear-cup construction and use a fully modular, user-serviceable design — every part can be swapped using common household tools, and the headphones carry a five-year limited warranty.

OLLO has built its reputation in the professional audio community for prioritizing tonal accuracy and repairability over consumer styling, positioning its products as analytical tools for engineers rather than lifestyle headphones. The company markets directly to studio professionals and home recordists, and counts a number of Grammy-winning mixers and producers among its endorsers.

OLLO has 2 products cataloged on Equipboard, including Headphones & In-Ear Monitors.