QSC is an American professional audio company founded in 1968 by Patrick Quilter and based in Costa Mesa, California. The company began as a storefront amplifier builder — early guitar amps carried names like the Duck Amp and the Quilter Sound Thing — before incorporating in 1975 as QSC Audio Products and pivoting to professional power amplifiers. Patrick Quilter's 1978 AC-coupled amplifier circuit patent, which allowed high-voltage transistors to mount directly to a grounded heatsink, helped establish QSC's reputation among live sound and installation engineers.

The company is best known for its powered loudspeakers and amplifiers used in live sound, DJ, house of worship, and commercial install applications. Flagship lines include the K.2 Series powered speakers (K8.2, K10.2, K12.2) with their 2000-watt Class-D amplifiers and onboard DSP, the KW and KLA line-array families, the E Series passive loudspeakers, and the TouchMix series of compact digital mixers. On the install side, QSC's Q-SYS platform combines networked audio, video, and control processing for venues, corporate spaces, and broadcast.

Beyond its own portable PA line, QSC supplies amplifiers and processors widely used in touring rigs and fixed installations, with the PowerLight switching-supply amplifiers of the 1990s marking its transition into a major force in professional audio. The brand is a common sight on stages, in clubs, and in houses of worship, and its gear frequently shows up in mobile DJ and band backline setups.

QSC has 89 products cataloged on Equipboard, including Power Amplifiers, Speakers & Accessories, and Subwoofers & Accessories. Their gear is featured by 17 artists, with the strongest followings in Rock, Metal, and Jazz. Notable users include Paul 'Wix' Wickens, Brian Gibson, and Omar Hakim. QSC's catalog spans the full price spectrum — from entry-level options to high-end flagships.