Key to the design philosophy of the new company was the use of synthetic materials for the diaphragm and surround of the drive units. KEF’s first speaker design, the three-way K1, incorporated drive units with foil-stiffened, vacuum-formed polystyrene diaphragms and the revolutionary T15 tweeter with a diaphragm made of Melinex (also known as Mylar in the US and Hostophan in Europe) – a ‘state of the art’ thin but strong polyester film. These breakthroughs inspired many new products, not least the Celeste, a ground breaking compact two-way design - the first really small hi-fi speaker. It went on to huge commercial success, ensuring the financial viability of the fledgling company. By the mid 1960s a comprehensive range of products was available from KEF to cover all applications including the Portable Celeste - a utility speaker aimed at schools and institutions, and the K1 and K2 baffles which customers could build into their own cabinets or mount ‘in-wall’ with the help of specially produced instruction leaflets.
In the mid 1960s a new bass/midrange unit was under development. For the diaphragm, Cooke and his development team set upon an entirely new material – Bextrene. This was a lightweight acetate plastic sheet derived from wood pulp, subsequently adopted by the BBC for the bass and midrange drivers of the LS5/5 monitor. As well as possessing the required mechanical properties, Bextrene was sufficiently stable to maintain its performance under typical variations in temperature and humidity. Bextrene woofer cones also produced a consistency of sound over a wide bandwidth, qualities which ensured their widespread adoption by other speaker manufacturers in the years that followed.
In 1966, after a period of intensive research and development, KEF launched the a new 5 inch bass/midrange unit (B110), and along with it came a ¾ inch melinex dome tweeter (T27). A larger 8 inch bextrene coned bass unit (B200) followed in 1970. The complete range of KEF drive units allowed great flexibility for the designer and they were subsequently incorporated, in differing combinations, into several million loudspeakers produced by KEF in Maidstone, and around the world by a plethora of other manufacturers. The B110 and T27 were utilised by KEF in the new Cresta bookshelf system and by the BBC in the diminutive but acoustically advanced LS3/5 loudspeaker. This outside broadcast monitor loudspeaker was later refined in 1975 into the LS3/5A – without doubt the most important result of KEF’s collaboration with the BBC. This revolutionary product set the ‘BBC Standard for Loudspeakers’, and has since acquired an almost mythic status among audio-lovers.
The Carlton monitor system was introduced in 1967 - a highly advanced design incorporating a 2.5inch bextrene dome midrange unit, acoustically loaded on its rear surface by a 33 inch damped flexible tube. The three-way Concerto arrived in 1969 bringing high-end performance, in an attractive package, into the mainstream loudspeaker market.
Throughout the mid 1960s, the small but talented design and production engineering team, (including Malcolm Jones - who later went on to form the loudspeaker parts supplier Falcon Acoustics), helped to bring Raymond Cooke’s engineering vision into reality. In 1968 this team was joined by Laurie Fincham, formally chief engineer at Celestion and Goodmans, who was instrumental in the development of KEF’s technical expertise throughout the 1970s and 80s.