Old days ...
These big enclosures were built by me, Kelvin Fleming, between 1972 and '74 (check the hair ...), and each unit comprised an upper and lower cabinet. The lower cabinets contained custom ordered 15" Fane Acoustics drivers with 18,000 gauss magnets and 4" voice coils. The top sections housed 8" Richard Allen CF8Ls with custom doped cones, Celestion MR500 midrange domes and (two) HF2000 super tweeters each side, both from the 'Ditton 66' model. The midrange domes and tweeters had adjustable level pots which were later replaced with stepped attenuators for better reliability. The crossover was very complicated due to the cascade type of design and the fact that it was four way, and filled much of the upper cabinet. The air core inductors feeding the bass speaker were twin 5.0 mH and the lower midrange twin 1.6 mH.
Overall weight was around 250 lbs per side.
The upper section could operate as a stand alone infinite baffle of three way configuration with (somewhat) limited power capability, the lower cabinet being what would be referred to today as a "sub-woofer", but it was more than this. When the Full Monte was engaged the upper section was fed with high pass and the lower cabinet rolled off at about 250 Hz, but the massive rise in midrange response of the 15" Fanes (due to the powerful magnets) had to be compensated for with the crossover, and also assisted in producing a huge sound due to the lower midrange weight. Only lengthy experimentation produced a result to the reasonable satisfaction of myself, the builder who understood little of the electromechanics involved at the time. Indeed, the technical parameters of the crossovers and the venting were based on the advice and hands on experience gained whilst working under the supervision of Dean Harrel, a co-director, and audio enthusiast of a company called Challenge Hi Fi in Adelaide S.A. 'Challenge Hi Fi' was formed by two audio hobbyists who had very different backgrounds. The other director and main motor on the business side being Steve Cotton. Dean was an audiophile and classical music aficionado and Steve had a background playing electric guitar in Adelaide bands in the '60s. The company specialised in importing many lines of their own from Europe and the U.K., and manufacturing many of their own loudspeaker designs on the premises, as well being the distributor for 'Interdyne' products from the Alex Encel stable. e.g. 'Celestion', 'Lux", 'Micro' and a swath of other quality products of the time such as 'Quad', 'IMF', 'Williams', 'SME', 'Shure', 'Duel', etc. In Hindsight, I feel that these were the last of the glory days of the Hi Fi enthusiast who's desire was to make their own stuff and tweak the best out of it, before the corporate world took the reins after the invention of CD in the early '80s. Everyone who worked in that store was either an audio enthusiast, or musician or both, with the exception of Steve's younger brother Chris, who being the resident tech, was encumbered with the often tedious task of fault finding and fixing less than stellar quality electronics! His favourite comment was: " ... everything's crap!" A number of people worked in the basement of the premises, building up loudspeaker systems. Terry Timothy (bass player), Nigel Sweeting (also a bass player). Frank Fuletti (drummer) and young Graham Rutterford, (ultra cheeky and smart electronics dabbler). We had lots of fun amongst the confusion. They were good days...
The overall sound was very smooth, and quite subtle for the size, but had a bass response the scale and majesty of which I have not heard since (not in my socio-economic strata at least) having a response down to around 20 Hz with virtually unlimited power capability. In hindsight the enclosures effectively boosted the bottom end to larger than life levels, producing almost infrasonic sounds from material which, on other systems, seemed not to have that much LF information. Ironically the speakers presented a very difficult load for the amplifier and the 40W Dynaco valve monoblocks being used at the time lacked control and impact. A high powered American muscle amp such as an Amcron DC300A, Phase Linear or similar kit did much more justice. Note also the high quality 'Shepherd' castors at the base of the enclosures. These were originally invented around 1945 and manufactured in various places by George Shepherd (Australian Patent 136548 lodged 10 September 1947) and were readily available in local hardware stores. Interestingly, they are now almost unobtainable in Australia, since the country has become a collective of profiteering importers of generic rubbish (A.K.A. a 'Service Economy'). Case in point, a very popular hardware chain that has managed to oust almost all competition much to the delight of the Australian people, which now sells no-name rubbish and calls it hardware.
These units still are now somewhat decommissioned, operating today as storage cabinets I believe, having been sold by me before moving to Melbourne to continue my musical endeavours in 1979. The owner now prefers open backed speakers, a move I can appreciate myself. Enclosing speakers always creates problems with unwanted resonances and strains on the cones. A large O.B. gives a much more open sound to a good speaker.
Since doing all this I have become an electronics technician after some study, and continue to be fascinated by the precarious art of speaker building and Hi Fi generally. My interest these days is much more focussed on music, musical electronics and guitars rather than Hi Fi and I continue to play music e.g. the link from this page. I still enjoy listening to a good sound system but the Hi Fi world is so profligate with bullshit it sometimes leaves me gasping. Examples of strange devices which claim to enhance a sound system are always around - inevitably built by portly middle aged men "Looking For The Answer......." Often the protagonists of this sort of thing are largely technically illiterate, with an attitude that borders on the psychotic. (go here for an amusing tale from the late '80s) Formally trained electronics engineers are often just as bad of course because if the maths says it's right - then it's right no matter how crappy it sounds - like saying "Oh any modern amplifier is pretty good thesedays....." Wrong!! Most commercial amps such as Surround Sound units are aurally horrible compared to a traditional budget NAD or Marantz. I guess most folks don't care anymore; content to listen to steely sounding i-Pods through those hideous white earphones. Over it...........live music is much more fun.
Photo taken by Peter O'Grady in Adelaide S.A circa 1974