Gary Pearce of Witchdoctor met Castle's managing director while selling hifi on weekends in Auckland. He bought Castle Harlech floorstanders, added Richmond 3i rears, a subwoofer and a center speaker, and many speaker purchases later still couldn't part with the Harlechs. Castle builds its cabinets as furniture, in real wood veneers chosen by eye and matched in mirror-image pairs. Inside many of them is Castle's other idea, quarter-wave loading, where the back of the bass cone feeds a pipe inside the cabinet instead of a short port. Castle says the pipe extends the bass without the boom that ports can cause in a room, and lets it keep its crossovers simple. Mark Gusew of StereoNET calls the Windsor Earl "a refined, smooth-sounding loudspeaker," and Pearce found the Knight 4 "very easy to listen to for extended periods." Castle suits listeners who play music for hours and want speakers that look like furniture.

Castle's current range is made in Britain in three series of two models each, and the Windsor Earl is the place to start. It is a standmount designed with Karl-Heinz Fink's team, and it works with modest amplifiers. A British Audiophile drove it with Musical Fidelity's 25-watt A1 and suggested the Hegel H190 may be an ideal partner, and Gusew heard more bass weight from a Cary SLI-80 tube amp. The step up is the larger Duke, for buyers who want floorstander scale from a standmount, and Adam Smith of Hi-Fi News was "unprepared for just how big they would sound." Give both models room. A British Audiophile settled on about a meter from the wall behind the Earls, and Smith found two feet a minimum for the Dukes and got the widest soundstage with them pointed straight ahead. He and Gusew both preferred listening with the grilles off.

Castle began on September 3, 1973, in Skipton, Yorkshire, and took its name and logo from the town's 11th-century castle. Wharfedale veterans founded it, among them Bill Escott and John Collinson, who had also worked at Quad. The Ear describes the early speakers as complete instruments, with drivers, crossovers and cabinet volumes developed together and finished in real wood. The first series included the compact Richmond and the flagship Howard floorstander, along with the Kendal and Conway. Hi-Fi Choice made the small Richmond a Best Buy in 1981 and gave the Richmond 3i the same rating in 2004. In 1990 Colin Walker's Winchester became the first Castle with a quarter-wave tapered pipe, and the new Walmer 2 floorstander, built in Huntingdon, Cambridgeshire, takes the pipe idea further. Fink had worked on the Richmond 3i as well, and in 2023 his Windsor series became the first of Castle's current British-made speakers. A British Audiophile called the Earl's sound "very smart voicing, and ideally what you'd wish for from a speaker that bears the Castle name."