Klein & Hummel was a German pro audio manufacturer founded in 1945 in Stuttgart by Horst Klein and Walter Hummel. The company built its reputation on studio monitors and PA loudspeakers engineered around acoustic research and precision measurement, becoming a fixture in European broadcast facilities, mastering rooms, and recording studios.

The brand is best known for its active studio monitors. The O 92 and the O 300 became staples of mastering and broadcast monitoring, prized for their flat frequency response and revealing midrange. The OY, introduced in 1967, is widely cited as one of the first active studio monitors with an active crossover and stayed in production for roughly two decades. Smaller models like the O 110 and O 410 extended the line into project studios and nearfield use.

Klein & Hummel was acquired by Sennheiser in 2005, and in 2010 its monitoring line was folded into sister company Neumann. Subsequent Neumann KH-series monitors — including the KH 120 and KH 310 — descend directly from Klein & Hummel designs, with the KH 310 essentially a rebadged O 300.

Klein & Hummel has 2 products cataloged on Equipboard, including Active & Passive Monitors and Effects Processors. Their gear is featured by 1 artist, with the strongest followings in Electronic. Notable users include Steve Bug.