Impressive 20lb Polk Center Channel CS245i

Matthew Polk, George Klopfer and Sandy Gross, graduates of Johns Hopkins, founded Polk Audio in Baltimore, Maryland, in 1972. The Monitor 7 of 1974 was their first model to succeed, and the Monitor 10 followed in 1976.

SDA. In 1984 Polk introduced SDA (Stereo Dimensional Array). A cable between the left and right speakers lets each one cancel the sound that crosses over to the wrong ear, for a wider stereo image.

Growth. Polk went public in 1986 and moved to new premises in Baltimore. It began moving manufacturing to Tijuana, Mexico, in 1988, and by 2012 Stereophile reported that Polk designed in the US and built in China.

New owners. Directed Electronics agreed to buy Polk in 2006. Polk later became part of Sound United, Masimo bought Sound United in 2022, and in September 2025 HARMAN, a Samsung company, completed its purchase of Sound United. The 2018 Legend series brought SDA back.

Monitor (1970s to early 1990s): the Monitor 4, 5, 7, 10 and 12, with A, B and C revisions.

SDA (1984 to about 1991): the SDA-1 and SDA-2 families, CRS, SRS and the later "TL" models.

RTA (1979 to 1992): towers such as the RTA 11t, with two woofers and two passive radiators.

RT and RTi (2001 onward): Polk's lower-priced lines. Our best-selling RTi10 towers and RTi4 bookshelf speakers come from here.

CSi centres and PSW subwoofers: the CSi3 centre and the PSW10 and PSW125 subwoofers are among the Polks we sell most.

LSi (about 2001 to 2010) and LSiM (2011): Polk's flagship lines of that decade, followed by Signature (2016), Legend (2018) and Reserve (2021).

SDA cable. SDA speakers need the interconnect cable between them for the SDA effect, and early SDA models need a common-ground amplifier. Make sure the cable comes with the pair.

Tweeters. Owners report that some SL3000 tweeters on the 1989 to 1991 SDA TL models leaked their ferrofluid and failed, and that Monitor-series pairs may carry mismatched factory or replacement tweeters. Check that every tweeter plays.

Surrounds. Some early Polks used foam surrounds, which rot with age; later models such as the RTA 11t and LSiM use rubber. Press gently on each woofer surround.

Everything we list is inspected, tested and serviced as required here, and comes with our warranty.