BACKGROUND Tannoy is famous worldwide for its innovative, unique and very accurate sounding Dual Concentric. A Dual Concentric speaker unit is very different from the standard speaker industry drive unit. It has the tweeter or treble unit mounted at the center of the bass unit so that the two units operate in total harmony with each other. Many manufacturers such as JBL, Altec, Urei, KEF, Pioneer, Diatone, TEAC, have recognized the benefits of the co-axial or concentric arrangement of woofer and tweeter to cover the whole audio band from a single apparent point source. None of them has solved the problem from an ideal acoustic engineering point of view in the way that Tannoy has. The construction and operation of the Tannoy Dual Concentric (upper case 'D' and 'C'!) is unique and provides benefits that other manufacturers cannot. The waveguide high frequency unit (so called because of the analogy in design to microwave engineering) has a smooth acoustic path through the center of the low frequency unit without problems due to masking or diffraction. The low frequency unit operates without obstruction, as the cone piston apex is well clear of the high frequency unit. Both units operate in harmony together providing a single point source covering the whole acoustic audio spectrum and in a way that recreates the original sound field better than any other system. Tannoy Dual Concentrics are by their very nature complex to manufacture and therefore you will not find them in a low price system. In this world you get what you pay for and therefore for the best type of speaker system you should be prepared to spend more. The results are demonstrably worthwhile even in the unfamiliar surroundings of an in-store trial.
THE FORMATIVE YEARS Tannoy was the trade name of a company formed by Mr. Guy R. Fountain in 1926. The name originates from a solid-state rectifier invented by Guy Fountain made from an alloy or mixture of Tantalum and Lead. This Tantalum-Lead Alloy produced the name Tannoy. The name stuck fast to the company's products over the years and eventually became the company name, Tannoy Ltd. >From 1926 through the recession of the thirties and during the Second World War Tannoy produced many different products all to do with speech and music communications. One innovative design was a universal speaker system designed for a travelling circus. The speaker requirement was for high quality speech and music for announcement and entertainment purposes in the largest travelling circus of Bertram Mills. The speaker had to be efficient because all the amplification was by tube amplifiers (design and built by Tannoy of course) and the power
supplies were derived from not very efficient motor generators and rotary converters.
THE FIRST TANNOY DUAL CONCENTRICS
THE MONITOR BLACK Drawing from his knowledge of high efficiency products made for the high quality public address market, the Chief Engineer, Mr. Ronnie H Rackham combined a high frequency compression horn drive unit concentrically with a 15" direct radiating bass driver. His skill in designing wide band horn systems married the two drivers together so that the flare shape of the 15" bass unit continued the flare rate of the high frequency unit. It was this important part of the design process that conceived a very low coloration horn device. Because the HF horn had a very large mouth diameter it had an inherently low cutoff frequency. The crossover point from bass to high frequency was selected at 1kHz; nearly a whole octave above the natural horn frequency lower cut off point, leading to previously unheard of low levels of coloration. In 1947 the first Tannoy Dual Concentric was born. It was designated the '15" Monitor Black', had a power handling of 20 Watts RMS, a voice coil impedance of 15 Ohms and a crossover point of 1 kHz. Magnetic gap fluxes were provided by a cast iron alloy magnet and were very high for a speaker of the 1940s at 12,000 gauss for the low frequency voice coil and 18,000 gauss for the HF coil. (10,000 gauss = 1 Tesla). At 20 Watts power handling in 1947 the unit was very well received and this, coupled with a sensitivity close to 92 dB for 1 Watt at 1 meter right up to the highest frequencies, was a milestone for the company in providing high quality speech and music capabilities in an efficient way. Six years later the unit was improved to 25 Watts power handling and the free air resonance lowered to 40 Hz to enable the unit to be used in encloses to improve the low frequency performance. The heavy, black crackle finish, overly engineered cast chassis was replaced by a gravity casting with much more open area to the rear to prevent rear reflections. The livery was changed to silver and in the autumn of 1953 the '15" Monitor Silver' loudspeaker from Tannoy was launched in a compound horn cabinet called the 'Autograph'. The previous 15" Monitor Black had an integral crossover network and line-matching transformer built into a square aluminum box mounted on the side of the chassis. All components were 'potted' in wax to prevent resonance and to protect the wax paper capacitors used at the time from moisture.
THE MONITOR SILVER
When the 15" Monitor Silver was announced, the crossover network was separated from the chassis to prevent interactions with the ferrous magnet parts. The 15" Monitor Silver was also used in the Corner GRF loudspeaker system launched in 1955. The 15" Monitor Silver was accompanied in 1957 by a smaller unit, the 12" Monitor Silver, which was the predecessor of the famous Tannoy Little Red Monitor launched in 1979. The Monitor Silver range of 2 units continued in development with improvements to power handling, sensitivity and free air resonance through 2 more generations before significant changes took place.
THE MONITOR RED
In 1958 the Silver range became the famous original Monitor Red series with a 10" Dual Concentric being added in 1961. Power handling figures were improved to 50 Watts for the 15" (25 Watts for the 12") and sensitivity levels kept well up at 94dB for 1 Watt at 1 meter to match well with tube amplifiers. The speaker units were designated: 15" Monitor Red LSU/HF/15-L 12" Monitor Red LSU/HF/12-L 10" Monitor Red LSU/HF/III-LZ A couple of significant things appeared here. The designation 'L' at the end of the type number stood for Low impedance. The 15" and 12" units had 15 ohms voice coils that most people today would take as high impedance. The 'L' designates that the unit is of low impedance with respect to a 100 Volt line system. The 10" version was a different story. This unit departed from the 2" LF voice coil used in the 15" and 12", using a 2.5" coil. The solution to the voice coil and magnet gap design (or motor design as we call it today) was optimum only for a low impedance coil. The resistance of the 'III LZ' coil was 2.8 Ohms. The unit was supplied with an impedance matching transformer to get the impedance up to 15 ohms to match a tube amplifier. When the early transistor amplifiers were introduced the primary of the transformer was very bad news for the output stage as it presented a short circuit to any DC offset condition. It is interesting that with today's robust amplifier design the best thing would be to drive the voice coil directly and get a very good damping factor and apparent sensitivity.
THE MONITOR GOLD
In 1967 the 'REDS' were upgraded to 'GOLDS' with the arrival of the Monitor Gold series. Power handling was now 60 Watts RMS for the 15" Monitor Gold but with sensitivity levels dropped back to 92* dB and, what is now considered the conventional impedance of 8 Ohms. The sensitivity was reduced as the best compromise in bass extension and available amplifier power. Cone weights were ncreased to get a low free air resonance as the units were being used in cabinets of either vented or infinite baffle (acoustic suspension) design. The original compound and rear horn loaded designs such as the Autograph and Corner GRF were cumbersome for the increasingly sophisticated domestic market. From 1947 to 1974 the front suspension design of the cone pistons in the Dual Concentric drivers had changed little. The relatively conventional looking corrugated paper surround at the circumference of the cone was a very sophisticated device. The importance in providing an excellent and well-damped cone termination was understood even in the sixties by the Chief Design Engineer, Ronnie Rackham. His surround design was at the forefront of cone manufacturing technology in that the surround edge was significantly thinner and more flexible than the cone body. This was achieved by screening the pulp mesh within the cone forming process so that fewer fibers were deposited in the crucial surround area. When the cones arrived at Tannoy a lengthy process involving glycerin and polyisobutylene with an acrylic barrier was devised in creating the correct cone termination properties with a high strength and compliance factor. In addition, a 'rug wool' strip mounted at the extreme perimeter of the surround provided an acoustic barrier. During the change from Monitor Red to Monitor Gold the high frequency diaphragm rear throat cavity was changed from aluminium pressing to a glass filled thermo set compression molding. This is one of the many design change clues that can date an old Tannoy Dual Concentric very accurately. Although the
chassis color generally followed the model changes through the years, export countries often had different combinations of design status and finishing color. Monitor Red units had a grey chassis and a red/pink rear magnet cover. Monitor Gold units were grey chassis with gold covers. These units were designated: LSU/HF/15G LSU/HF/12G & LSU/HF/12G/RS (rubber surround) LSU/HF/III LZG (LSU/HF/III-LZ2GU & GH) In 1974 a radical approach to surround design was taken and the cone structures of the 15" and 12" completely redesigned for the HPD Series. 'Tannoplas' surrounds were fitted to 'Girdacoustic' reinforced cone structures in a wildly enthusiastic attempt to market the mystery of loudspeaker design to a world that was fairly ignorant of the Dual Concentric principle. What the world did not grasp was that most recorded music available was being produced on the Tannoy Dual Concentric using either Monitor Red's or Monitor Gold's. All the music at EMI including Abbey Road and most of the Decca Classical output was produced using Tannoy loudspeakers.
THE HPD 'Monitor High Performance Dual'
A major redesign of the Monitor Gold led to the 'Monitor High Performance Dual' HPD Series. Power handling was improved considerably by using high temperature adhesives in specially set up Tannoy coil winding and heat treatment sections. Sensitivity was maintained at 92 dB for 1 Watt at 1 meter while moving cone masses increased to give the correct 'Q' values for a range of 5 cabinet models. Three different drive units were designed and manufactured for these cabinets: 15" Monitor Dual Concentric HPD385 12" Monitor Dual Concentric HPD315 10" Monitor Dual Concentric HPD295 The numbers after HPD refer to the nominal diameter of the unit in millimeters. All units were 8 ohms and also supplied with crossover and terminal panel as kits for the professional market or home constructor. The crossover network is worthy of mention as there were some sophisticated circuits used for controlling both the level of energy from the HF unit and the degree of roll-off above 5 kHz. An autotransformer was used to match the relatively high impedance of the HF voice coil (10 Ohms resistive, approximately 18 Ohms above 1 kHz). Many HPD's were built into large cabinets for studio monitoring by a UK company called Lockwood. Such models as the Lockwood Major, Lockwood Universal played a very significant part in the development of the world's recorded music as these were bought almost entirely by the professional studios. For example, most of the successful records made by Mickey Most at RAK Records were produced on Lockwood Monitors with Tannoy Dual Concentric drivers. Trying to increase sales, especially to export countries, Tannoy produced a range of 5 cabinets using the HPD unit designated the 'A' variation. These were: ARDEN using HPD385A 15" Dual Concentric BERKELEY using HPD385A 15" Dual Concentric CHEVIOT using HPD315A 12" Dual Concentric
DEVON using HPD315A 12" Dual Concentric EATON using HPD295A 10" Dual Concentric As well as being universally accepted around the world this range was exceptionally successful in Japan between 1975 and 1980 helping to establish Tannoy in the Far East as a manufacturer of very high quality loudspeakers.
ANISOTROPIC BARIUM FERRITE
From 1947 to 1978 Tannoy Dual Concentric drivers used a metal magnet made from an alloy of nickel, aluminium, cobalt and iron. Although of great strength this magnet material was not very efficient in power to weight ratio and difficulty in the world supply of cobalt was generating a problem in maintaining smooth production at the Tannoy factories in West Norwood, London and Coatbridge in Scotland. During the latter part of 1977 the decision was taken by Tannoy to design a new series of Dual Concentric drive units using Anisotropic Barium Ferrite magnets. This material is more efficient in power to weight ratio and had a much higher coercive force leading to fewer problems in demagnetization under high power or low storage temperatures. New magnet charging equipment was purchased to supply the much higher magnetizing force needed by the new material. Magnets are supplied unmagnetized to Tannoy so that the magnet can be magnetized with all its metal pole pieces in place for higher gap field strength. The process of magnetization is called 'charging' the magnet and takes place inside a heavy coil that generates an exceptionally strong magnetic field for a faction of a second to align the magnetic domains within the material. The first unit to emerge with the Anisotropic Barium Ferrite magnet system was a very high power high sensitivity midrange unit used in the Buckingham and Windsor cabinet models. This unit subsequently went on to be used in the Buckingham Monitor and, with further modifications in high power music concert rigs throughout Europe. >From 1978 the pace of research and development at Tannoy increased many times over. A strong engineering team was assembled at the Scottish factory that was by 1980 the central focus of the company. A long-term plan was developed that sought to improve every specification of the famous Dual Concentric units while developing specialist units for varying applications. This was to remove the inevitable compromise of using only 3 different units in a variety of applications.
The cornerstone of the hi-fi Dual Concentric loudspeakers was the 10" unit with a revolutionary Polyolefin vacuum formed cone piston. Domestic hi-fi required smaller cabinets in the eighties and so a smaller unit was developed with very low coloration, high compliance and power handling and wide dispersion. Together with an Auxiliary Bass Radiator design (ABR) a range of Hi-Fi Dual Concentric cabinets appeared: T225 Mayfair using 2528 Dual Concentric with 2500 ABR T185 Dorset using 2528 Dual Concentric with 2500 ABR T165 Chester using 2528 Dual Concentric T145 Ascot using 2528 Dual Concentric
This range was launched in 1978 as a replacement to the Arden - Eaton range and proved successful in increasing export penetration. However it was too much to ask of a 10" Dual Concentric even augmented by a 10" ABR to compete with the sheer sound reproduction capability of a 15" Dual Concentric in a big cabinet (the Arden or Berkeley). Those markets that had a particular affinity for the 15" Dual Concentric and its fine ancestry demanded its continuation.
STUDIO MONITORS - SRM series In parallel with the hi-fi developments during the 1977 - 1979 period a separate team were working on Dual Concentric loudspeakers for the Professional Studio Monitoring market. Although a survey at the time showed Tannoy to have the largest share by far of the studio market it had never advertised its Duals for this purpose. The Duals had been fitted to Lockwood cabinets or fitted into similar cabinets by end users. The engineering team were confident that standards could be improved yet further using the Dual Concentric in a purpose designed and matched cabinet, and in 1979 at the AES Convention in Brussels, 3 models were unveiled specifically for the high power studio monitoring applications for which Tannoy had been famous. The famous Tannoy advertisement stated: "After 53 years of Research and Development, Tannoy is proud to present its Studio Monitor range." Two new 15" Dual Concentric units were available. One was the 3838, a high compliance, lower free air resonance Dual for the TV and Broadcast marketplace where bass performance is crucial but ultimate levels of sensitivity are not required; and the other, the 3808, was a low cone piston mass, high sensitivity version for high sound pressure level monitoring and track laying. A third system was also launched using the 2548 high power midrange Dual coupled with two 12" bass drivers (type 3126) in a 300 litre cabinet. To control HF dispersion the extra degree of freedom in having a midrange Dual Concentric in the Buckingham Monitor allowed a sophisticated wave front shaping Waveguide to be fitted - the first acoustic lens system ever fitted to a Dual Concentric. In 1980 following hot on the heels of the 3 Professional Dual Concentrics were 2 smaller Professional versions for nearfield monitoring, the 3149 used in the SRM12X and Little Red Monitor, and, the 2558 used in the SRM10B. These additions completed a line of 6 Studio Monitors that cemented Tannoy Dual Concentric units onto the world map in their own right. Recorded music had been using the Tannoy Dual Concentric principle for years but had not realized it. With purpose designed cabinets and high power crossover systems the full potential of the Dual Concentric could be realized. The 1979/1980 Studio Monitor Range: Buckingham Monitor using 2548 Dual Concentric with 2 x 3126 Bass. Classic Monitor using 3828 Dual Concentric. Super Red Monitor using 3808 Dual Concentric. SRM15X using 3808 Dual Concentric. SRM12X using 3149 Dual Concentric. Little Red Monitor using 3149 Dual Concentric. SRM10B using 2558 Dual Concentric. Following the success of the big Duals in the domestic markets in the Far East during the 1975 to 1980 period, Tannoy decided to maintain a high profile by developing loudspeaker systems with cabinets
large enough to make full use of the Dual's capabilities, whilst being aware of the domestic space available for large speaker systems. Between 1980 and 1982 three smaller footprint domestic models were introduced using the same research and development pioneered for the professional line but with slightly less demanding power handling specifications. Three more very radical domestic systems were also developed as a trial in the marketplace for something very special in appearance and performance. The small footprint range consisted of: Arundel using 3839 15" Dual Concentric Balmoral using 3128 12" Dual Concentric Caernarvon using 2558 10" Dual Concentric
THE 'RADICAL SYSTEMS'
The radical systems consisted of: Westminster using 3839W 15" Dual Concentric GRF Memory using 3839M 15" Dual Concentric Edinburgh using 3149 12" Dual Concentric Two systems are worthy of note. The GRF Memory was based on some old drawings found in Guy R. Fountain's office when the final removal from the West Norwood site was in progress. It is believed that Mr. Fountain himself made the sketches in the days running up to the sale of the business to Harman Industries in 1974. Rather than see such interesting ides go to waste the Design team in Scotland thought it would be a good idea to use the concepts to produce a speaker system worthy of his name. This they did in the Guy R. Fountain Memory. The Westminster is also worth a further look. In the early eighties the hi-fi industry seemed to be concentrating on smaller cabinets with increasingly low levels of efficiency. The Tannoy Engineering team was keen to demonstrate that a large an effective compound horn loaded system could provide a level of sophisticated reproduction that no other type of system could get close to. They were part of only a handful of speaker engineers around the world who were capable of designing and engineering such a system. And so the Westminster was created- 250 pounds weight of speaker with a transient attack and low frequency performance that many people in the world could not believe. Music lovers had to be prised away from the demonstration seating at exhibitions, where Westminster's were being put through their paces, to make room for the queues outside. The success of the Westminster, GRF and Edinburgh in the Far East spawned a smaller design named the Stirling, introduced in 1983. In a way this speaker was a return to the concept of the original 111LZ using a 10" Dual in a bookshelf size cabinet. The Stirling completed the "radical" range of speakers and the line was designated the Prestige Series.
THE WILDCATS : P - SERIES
In 1984 the Research and Development team at Tannoy wanted to prove that the Dual was an excellent solution to very high quality live music performance venues. Clearly, with the sizes of magnet and levels of efficiency available it could not compete with the outdoor rock concert systems from Altec, Meyer and JBL but there was a niche in the cabaret and small club market where the sound quality needed to be considerably higher than that to which people were accustomed. Specially adapted Duals were designed that had more power handling and greater sensitivity than had ever been produced
before by Tannoy. These were fitted to a range of very robustly made cabinets with reinforced handles and corners suitable for mobile cabaret or fixed contractor installation work. The line was christened the 'Wildcats' and was the start of a very successful venture into high quality voice and music provision for sophisticated venues such as clubs, theatres and churches. The Dual Concentric is a unique speaker system ideally placed for communication and intelligibility in difficult acoustic surroundings. The dispersion character (directivity) is much more constant throughout the audio band than with most other systems. Therefore more direct sound reaches the listener than reflected sound and the intelligibility of the reproduced program material is greatly enhanced. The directivity characteristic also prevents excitation of troublesome room resonance associated with the reverberation time of room acoustics. Intelligibility and communication ability in halls and theatres is measured in 'Alcons' or 'percentage alcons'. The measurement is a quantitative analysis of the hit rate of a listener in the hall interpreting different words that have similar vowel and consonant sounds. A perfect acoustical environment would score 100%. The Dual Concentric system is notoriously good at providing the highest percentage alcon figures in any environment when compared to the competition. The Tannoy Wildcat range consisted of the following speaker systems: Lynx using 3169G two 12" high sensitivity Dual Concentrics in a double cabinet. Bobcat (B50) using 3169R 12" high sensitivity Dual Concentric in a single small cabinet. Puma (P100) using 3805 15" high sensitivity, high power Dual Concentric. Jaguar (J200) using 3809 Puma driver in a larger cabinet for deeper bass. Panther (P200) using 3859 15" Dual Concentric in a front sectored horn cabinet. Cougar using 3859 15" Dual Concentric in a floor wedge monitor. Lion (L300) using 15" bass unit in a coupled cavity bass bin. Cheetah (C150) using 15" bass unit in a small coupled cavity bass bin. Leopard (L200) using 15" bass unit in a direct radiating bass bin. The original Wildcat series was split into two ranges in 1987 to create a dedicated road proof MI cabinet series and a specialist contractor's line for permanent installation. In 1985 Tannoy started test marketing the high-output Dual Concentrics of the Wildcats into the more domestic end of the market. The Impulse Series was created using similar Duals to the Wildcats in more acceptably finished cabinets for home use. The series was not considered a major success but out of the work in engineering, a new high power studio monitor was developed - the FSM. The FSM was designed to sit at the top of the studio monitor line that was being improved and developed by Engineering for launch in autumn 1985. Many improvements had been worked on in the period from 1980- to 1985 and the time had come to incorporate all enhancements into the new range. The range change is signaled by the move from Super Red Monitor to Super Gold Monitor. Edge would coils, higher power and thermal handling, improved levels of sound quality and a 'faster, tighter' sound quality contributed to the success of this line.
>From 1985 Tannoy abandoned printed circuit boards and wafer switches in the crossover designs. A significant amount of research had shown conclusively that the layout and mechanical design or a high power speaker crossover was vital. Listening tests were carried out with great precision to isolate some of the aural effects encountered. The Tannoy R & D department concluded that: Printed Circuit Boards are detrimental to sound quality. Star earthing is of paramount importance.
Components must be held down securely to prevent microphonics. Wiping contacts and switches downgrade sound quality significantly. Gold plating of electrical contacts is beneficial to sound quality. Connecting cables can have audible effects. In 1985 the introduction of the Super Gold Monitor series and a top end monitor called the FSM commenced, replacing the Super Red series. Simultaneously a gradual change over in other products to 'Hard Wiring', eliminating printed circuit mounted components and, 'High Current Switches' using gold plated screw terminals, for which many worldwide patents were granted, was undertaken.
In 1986 a smaller model was slotted in at the lower end of the Prestige Range called the Greenwich using a newly developed 8" Dual Concentric, and a similar Dual Concentric drive united for the DTM-8 (8" Dual Concentric Desk Top Monitor). The introduction of the new 8" Dual, designated 2008C for the cast chassis version and 2008S for the rigid steel version, was another milestone for Tannoy. The 2008 used a split magnet system - separate magnets for LF and Concentric HF portions of the driver. This gave greater manufacturing versatility and commonality with other components making the 2008 more economical to manufacture. Previously all Tannoy Dual Concentric drive units used the single magnet philosophy pioneered by Ronnie Rackham in the late forties. With the advent of very high precision, high-pressure zinc die-casting processes during the eighties an extra degree of flexibility was beginning to appear; first in manufacture and then in design of the Tannoy Dual Concentric.
As explained earlier the large cast metal magnets were abandoned in 1978 in favor of Anisotropic Barium Ferrite. However there was a considerable lobby from traditionalists that the cast metal magnet Dual Concentric units had a certain sound quality that was impossible to reproduce in ANY other type of speaker design. A research project was initiated in 1988 to attempt to quantify this feedback. The result was a recognition that the cast metal magnets were acting as a shorted turn around the coil thereby minimizing flux modulation. For the aficionados and traditionalists a version of the Dual Concentric was designed and engineered with a new Alcomax 3 metal magnet made from an alloy of cobalt, aluminium, selenium and ferrous iron. This unit was put into a very prestigious model of the Westminster, the Westminster Royal, and into a traditional period cabinet named the Canterbury. All the knowledge learned so far in the Tannoy Engineering department went into these models resulting in spectacular performance and acceptance into the market.
RHR LIMITED EDITION
Tannoy decided to honor its principal mentor and now retired Chief Engineer in 1986 by asking him to design a period cabinet with a traditional rear folded horn. This project was completed by Ronnie and launched as the RHR Limited Edition. Only 111 pairs were made and were actively sought around the world. In response to overwhelming demand a further small quantity were produced with subtle appearance design characteristics and named the RHR Special Limited Edition. They change hands now for
a premium. Although Ronnie had passed retirement age he was keen to maintain a place in the Tannoy Design Team. He regarded it as a special honor to be able to play a leading role in the cabinet design of the Canterbury 15 and Canterbury 12. Ronnie passed away peacefully in December 1990 after an illness in which he showed the same practical fortitude and great strength of character that he had brought to the whole Tannoy team over more than 40 years service with the Company. In 1989 the pace of Dual Concentric innovation increased considerably. The two magnet system approach pioneered in the 2008 was carried a stage further with the introduction of Waveguide principles.
A new 8" Dual Concentric was conceived, the 2025, used in 3 domestic hi-fi cabinets: DC1000 using 2025 Dual Concentric in 25 litre cabinet. DC2000 using 2025 Dual Concentric with 2026 bass in 35 litre cabinet. DC3000 using 2025 Dual Concentric with 2026 bass in 50 litre cabinet.
DIFFERENTIAL MATERIAL TECHNOLOGY
A separate research project had shown amazing results in Differential Material Technology, the science of combining different materials to achieve the required acoustic properties at strategic places in a speaker design. DMT coupled with the new 2025 design put Tannoy firmly on the worldwide map for the Dual Concentric system performing in small footprint domestic cabinet systems. At last the population could listen to recorded material and be assured that they would hear everything that the artist intended.
The Waveguide theory and research started in 1989 for the 2025 was developed in an increasingly sophisticated way using Computer Aided Design and draughting techniques coupled with mathematical modeling of Waveguide principles. Much progress was made during 1989 and 1990 resulting in a very special and totally different approach to the HF section of the Dual Concentric. The 2025 Dual Concentric provided the clues to Tannoy's direction but when the new 12" and 15" Dual Concentric drive units appeared in the Monitor Series System 12 and System 15, people realized that Dual Concentric design would never be a traditional approach again. A new range of professional monitoring systems was introduced in 1990 based on Waveguide principles: System 215 using 3833GG 15" Waveguide Dual Concentric with separate 3834 15" bass (Soffit mount monitor). System 15 using 3833GG 15" Waveguide Dual Concentric (mid field monitor). System 12 using 3133GG 12" Waveguide Dual Concentric (mid field monitor). System 10 using 2525GGG 10" Waveguide Dual Concentric (near field monitor). System 8 using 2025GGG 8" Waveguide Dual Concentric (desktop near field monitor). System 2 using 0259 tweeter and a 1668GG bass/mid 2 way discrete system (d
monitor). All the system series cabinets had a revolutionary design appearance and had all the latest thinking in DMT cabinet design.
Also in 1990 a new range of Wildcat replacements were introduced using more robust versions of the Duals developed for the System series. These cabinets were designed specifically for the sound and video contracting market providing very high sound quality with unequalled robustness. An innovative cabinet was designed with a trapezoidal shape incorporating an aluminium extrusion housing integral flying points to suspend the cabinets safely above an audience. The whole suspension system was rigorously safety tested and has a national certification of safety. The Contractor Series was given the code system in engineering of CPA and this has stuck with the development right out into the marketplace. The range consists of: CPA 15 using 3836 15" high output waveguide Dual Concentric in a trapezoidal cabinet. CPA 15FM using 3860 15" high output Waveguide Dual Concentric in a compact cabinet. CPA 15.2 using 3861 two very high power 15" bass units in a rectangular bass bin. CPA 12 using 3134 12" high output waveguide Dual Concentric in a very compact trapezoidal cabinet. CPA 5 using 1501 5" ICT Point source drive unit in an exceptionally compact easily mounted molded cabinet. Of the range the CPA 5, the last one to be introduced in May 1991 at the NSCA Show is worth further investigation. The HF unit of this tiny driver operates on entirely different principles to all the other Tannoy drive units. The HF driving diaphragm has no coil, but a 'skirt' projects from the bottom of the diaphragm. The skirt is immersed in the same magnetic field as the LF unit coil and energy is induced into it from the LF coil. The crossover point can be set by the LF coil parameters and the diaphragm diameter. Eddy currents in the skirt which acts as a shortened turn similar to transformer theory effectively drive the HF diaphragm. The unit is therefore exceptionally robust with no possibility of HF burnout, a common problem with systems of this size and use.
The potential in the design of the Westminster Royal for a superb performance loudspeaker was well demonstrated with the incorporation of the Alcomax 3 cast alloy magnet system. The longer HF horn resulting from the increased magnetic length of the magnet gave an even better match to the acoustical front loading of this very complex and special cabinet. To take full advantage of the Dual Concentric drive unit the cabinet was specified as birch plywood throughout and to compensate for thicker internal partitions the whole cabinet and low frequency horn mouth area was increased accordingly. In addition to the increased height of the cabinet distinguishing the Westminster Royal from the Westminster HW the solid walnut top and bottom moldings were sharpened in profile and subtle inlays of burr walnut were added to the front baffle. Increasing awareness of the effects of the purity of the copper interconnecting wires during associated research projects pointed the way for all the internal wiring in the Westminster Royal to be specified as Van Den Hul cable. Careful listening tests
determined the gauges of cable in various areas; even the connecting wire integral with the drive unit HF section was re-specified. The result was another landmark in loudspeaker design and performance and is recognized throughout the world as one of the finest loudspeaker systems ever to have been produced.
THE SIXES SERIES
The SIXES were introduced at the Consumer Electronics Show in Chicago in June 1991. This range of seven models comprised three discrete 2-way speakers and four Dual Concentric models. Of particular note was the introduction of a 6.5" Dual, the smallest that Tannoy had ever designed. The range was to replace Series 90, but with the incredible pace of development on Dual Concentric drivers most of the range used either the 8" or the 6.5" Duals, the two top models having both driven bass units and Mass Tuned Passive Cones to produce very low frequencies. Much research had gone into this method of getting a much lower fundamental tuning of the cabinet and new techniques and materials were becoming available. Of particular note in the Sixes Dual Concentric drivers was the use of injection-molded cones. Most manufacturers were content with vacuum forming cones because of the economy of the tooling. Tannoy realized that the vacuum forming process could not obtain the optimum profiles required to make the next quantum leap for the Dual. Very expensive injection molding tooling was developed and both the 8" and 6.5" cones used this new technique. Yet another first for Tannoy was seen in the surrounds of the SIXES bass units and Duals. A very special and secret technique for making the roll surround an integral part of the cone profile resulted in both excellent acoustic matching of energy in the cone and surround and gave a much smoother transition for the HF wave front as it propagated down the profile. The HF unit at the heart of the Dual Concentric drive unit is broadly similar in diaphragm and coil design to a direct radiating unit. However the energy from the diaphragm is matched to the air load by creating a spherically expanding wave front. This ensures that the directivity is even more constant and symmetrical and the whole system produces an incredible stereo image. The perfectly spherical wave front is generated by the Waveguide at the throat of the LF unit so that the energy then propagates down the carefully arranged flare of the injection molded LF cone, which itself is optimized to ensure a smooth and extended response well integrated with the bass/midrange energy from the LF unit. The SIXES Dual Concentric loudspeakers consist of: 609 using 2033l 8" Dual Concentric 611 using 2033 8" Dual Concentric, 2035 8" bass 613 using 1662 6.5" Dual Concentric, 1663 6.5" bass, 1664 6.5" MTPC 615 using 2033 8" Dual Concentric, 2034 8" bass, 2037 8" MTPC
A few comments on the Black, by Kerry: Firstly, the 1953 debut of the Silver makes sense. Information that the Silver came out in 1950 is wrong. The comment that the Silver's frame ( basket ) is " much more open to the rear " is also wrong. As a matter of fact, the Black's " over-engineered " frame is far more ' open ' than later Tannoy baskets. The Black's magnet's cast-iron ( steel ) alloy the author mentioned is Alnico. I was told by a very reputable source that the earliest Blacks have a double ring magnet made of Alnico II. I have an early Black and it does have a double magnet - the seam is quite evident. Apparently, only about 150 units were made in 1947 before Tannoy switched to one-piece ring magnets of Alnico V alloy in 1948. Flux levels in the gaps were not increased in the ' improved ' Blacks ( even with the higher grade alloy ) as the new magnet was cast to be slightly smaller Early Blacks had the frame mounted crossovers. The ' xover box ' is steel by the way - very magnetic - not aluminum. Later Blacks had outboard crossovers. Neither style used wax-potted cases. No electrolytic caps either. Only high quality ' can ' oil caps. No " line matching transformer " either... not one for high voltage lines anyway, that's an autoformer. The Black's xover also has a HF potentiometer. Also, no mention was made of the 12" Black Dual Concentric.
A few comments on the Gold, by Hans:
The efficiency of the 15 ' Monitor Gold was not 92 dB SPL, but 94,8 dB SPL average anechoic. The specified power handling was not 60 Watts, but 50 Watts RMS open frame power handling: outside a cabinet. Built into a cabinet power handling could increase to 60 Watts. These parameters were supplied by Tannoy in all brochures and technical references, as you can see at this website.