The heart of today's Harbeth sound is our unique, Patented, RADIAL cone material. It has an interesting legacy. On 19 March 1976, our founder, H. D. Harwood of the BBC Research Department, filed a Patent application (1563511) claiming that polypropylene could be used as a loudspeaker cone material, now the de facto cone material throughout the global audio industry. The Harbeth company was formed (see press release) to commercialise his invention, and to sell his knowledge as monitor speakers back to the BBC. However, in 1994/5, a superior material was presented to Harwood and analysis of its improved properties led Harwood to abandon polypropylene and adopt the new TPX material in the forthcoming HL Monitor Mk4, and later in my (A.S.) original Compact and HL5. In 1990, concerned by the scarcity of supply of bought-in cones, we won a British Government Science & Engineering Research Council (SERC) Research Grant. This project allowed us to thoroughly examine alternative material solutions concluding that there was no undiscovered 'off the peg' wonder material, and to inventing and Patenting our own plastic formulation, called RADIAL [from Research And Development In Advanced Loudspeakers]. RADIAL is still unbeatable for clarity and resolution.
It came to light (July 05) some fifteen years after our project commenced, that unknown to us, the BBC had developed in secret an engineering approach almost identical to ours, but were tied to readily available vacuum formed polypropylene. Our breakthrough was partly in the RADIAL material itself, and partly in the move away from vacuum formed cones to our injection moulded solution.
This is the introduction page of Harbeth's Dudley Harwood 1976 Patent for the use of polypropylene to make loudspeaker cones. As far as we know, this Patent has expired and may have been rather too tightly drafted. It is also noted that it was claimed that polypropylene would make a wide-range drive unit, an echo of the BBCs monitor speaker from the 1940/50s. Perhaps this would have been technically feasible, but there is no mention of its colouration performance.
The first announcement of the forming of the Harbeth company in 1977- based on Harwood's polypropylene patent.
This is the end of Part 1. Part 2 continues with Tech Talk 10.