A number of enthusiasts prefer single speaker designs driven directly. The proprietor of a local B&O dealer, Jabez Gough of Goughs' (no longer extant), came up with a design (1961 UK patent 912,430) using 8" drivers that generated much interest. This consisted of a cabinet with hinged lid to direct the sound (a perhaps crude precursor to acoustic lens technology?), with ports to either side of the speaker which was mounted on the top, under the lid. Importantly, perhaps acknowledging the variance in speaker spec, it was held that dimensions, including that of the seams was not critical, although the author acknowledged that a lighter cone and coil mass could improve. Shop-supplied units would use the customers' choice of speaker. Surviving speakers can be mounted with a variety of other 'exotics' like the 25W 16R Lafayette SK 212, one type used to effect as a replacement being the Soundlab 8" (20cm) bi-cone bass unit (8LUX, res 40Hz). Larger versions seen included the Goodmans' twin-axiom 10/12 speakers (bi-cone).
Given the limitations of sound sources then available (including non-stereo FM) this author did not find the resulting sonic performance disagreeable. One critic suggested that the inclusion of a coil of 24 x 24 x 1" fibreglass below the speaker reduced a 'boxiness' quality.
A reviewer (Audio, December '73, PDF available) wrote positively of the better dual versions demonstrated in Goughs' custom built listening room. These used Goodmans Axiom 80 units.
This arrangement is well suited to larger rooms where speakers are not expected to be set against walls, say when the listening/seating area is in the middle or set to one side. It is felt that the major contribution of this approach was that it demonstrated that for effective domestic bass responses, speaker cabinets had to exceed two feet on at least one dimension and that the acoustic energy could be focussed, or 'tuned', then increasing the perceived efficiency of the system, important if overdriving was to to be avoided.
A suitable amplifier could be the Leak Stereo 20, contemporary Quads, an Armstrong or the later Rogers' Cadet. Solid-state designs with low level cross-over distortion like the Linsley Hood '69 class A could add definition. Sustainable maximum amplifier outputs would then generally sit between some 3-10W, more than sufficient even today to have neighbours complaining and then arguably presenting sufficient 'headroom'.
If time and resource allowed this design to be revisited, emphasis would be placed on stiffening the structure with corner joint battens and a brace on the mid-line between the larger panels. The baffle board should exceed 5/8" (16mm) in thickness. Damping filler would probably have to be matched to the drivers, although a lining on two adjacent sides of the central chamber might meet most needs. The speakers can then each have their own terminals so that testing and series/parallel combinations can be made easily, although it is expected that a series arrangement would be best. Because of their near horizontal disposition, protection of the cones is desirable and can be done with an acoustically transparent fabric that advisedly should be liquid proof. This, if made detachable, will allow the drivers to be 'top-loaded' easing replacement and flexibility will be enhanced if castors are added.
For vinyl, the system was driven by a Miniconic cartridge on a SME headshell on a custom-built low-mass, low friction gimbal suspension tonearm whose extra length was intended to help reduce tracking trajectory errors, mounted on a Garrard 301 set on concrete.
The screened leads giving a complete run to the amplifier from the cartridge are 'untidy' to prevent as much of their elasticity interacting with the arm (torsion). Ideally these should pass through the pillar but are too thick for this. Work in progress is further indicated by the pillar base plates' securing method. No bias compensation was possible, this area still being explored by manufacturers. For example, advice in the SME 3009/12 instruction manual recommended that the complete motorboard be tilted 'so that the edge of the turntable where the pick-up enters the record is 3/8" lower than the point diametrically opposite. This looks a little unusual at first if you have been accustomed to a level turntable'. Adopting this approach could increase bearing noise.
A B&O 2000 open-reel tape deck then fed a Trio 4002 which drove the speakers. These had, for the time, very flexible preamps allowing the use of multiple record and tape decks. The PA, despite its' many limitations especially in terms of component ratings typical of the day, 'delivered' for a large number of users. Note that the output electrolytic is included in the feedback. The Kenwood is a close match.
Thermistors mounted on the heatsinks were paralleled with the bias adjust pot. Contacts a - a' are in series with a 10k R and switch in tandem with the mains on-off. Considering the relative fragility of the output stages, protection ensures survival. The long wiring runs to these could only add to the colourations. The view below shows how not to layout an output stage.
It would be interesting to put the same system today on a 'scope to determine to what extent the different elements affected the sound quality, but what was apparent even then was that the choice of mechanical transducers (cartridge, speakers) principally contributed to the sonic quality, although the reviewer did note a lack of treble compared to the fullsome bass. The addition of tweeters is easy given the size of the baffle, unless another arrangement is required.
The author spent many school dinner hours drooling at Goughs' shop windows (around the corner from the school) which very probably contributed to the later involvement and interest in hi-fi and sound although price tags in guineas (1gn = £1 1s/£1.05p) did not happily reside with a parents' concept of pocket money.
Jabez' sons, Julian and Stephen, have created a very informative website; the 'historical and technical background' to the design can be found here.
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