I have to credit again cabinetmaker extraordinaire Jean-Paul Guy for sending me his complete file, including original drawings and hand-written notes from Jean-Claude Fourrière, the founder.
Dear readers, this is all pre-CAD, email and Internet. We didn't have mobile phones, and most communications were via landlines and fax machines, or slow mail...
Just that alone meant that it took time to get anything done, and mistakes were costly, very...
In most loudspeaker systems the Deccas were used in a passive configuration Later he developed the ALH full range plasma loudspeakers.) Fourrière used the Decca London Ribbon from 2000 Hz. Decca Special Products in England authorized him to use the denomination DECCA and he named his creation Decca AL2000. It was a 3-way system with complementing units from Audax (HD24 and HIF13). He also designed a 2-way system at the time: DECCA AL1500 with crossover frequency of 1500 Hz. The panels of the cabinets were heavily damped with sheets of lead. Photos below courtesy of www.soundfountain.com
He ended up sending me a number of great photos that he has given permission to share with you, you insatiable lot of hifi nerds and loyal readers of this blog!
This is a perfect example, as the REF 65 in the catalogue above shows both midrange drivers as domes (from SEAS), but this early version (my guess...) uses a MP14RCY from SEAS polypropylene cone. This, I believe, would have been a lot easier to crossover to the 24cm from Audax in the separate but integrated subwoofer. I have personally experimented at the time with a Dynaudio dome midrange and found it very difficult to use for that reason (and I have never been a great fan of Dynaudio drivers, or finished speakers for that matter...)
Although we do not have the value of all components, reverse engineering from the capacitors values and the frequency response of the drivers suggest crossover frequencies of 300 Hz for the woofer at 12dB/oct, 2000 Hz for the midrange and the HD100 at 12dB/oct, then around 4.5Khz for the TW74 at 6dB/oct. Various other resistors and capacitors may have been used to adjust levels and impedance compensation on the TH74, a good way to get reed of a nasty resonance. We might do some more research to clarify, or if somebody has the schematics, then we would be sorted...
I do not have a review of that speaker, although I have a number of them for other speakers in the range, which I will publish in a second episode to be published in the coming weeks.