Haden Boardman traces the history of Tannoy dual concentric loudspeakers and gives a potted guide to cabinets up to 1974.

There is but a handful of names that are truly synonymous with hi-fi, those that were there at our industry's birth, - founder members if you like. One of those is Tannoy, whose name is listed in every English dictionary as 'a type of public address system'. The company was set up in 1932 by Guy R. Fountain, and the name is actually abbreviated from Tantalum Alloy, a material the company used to make its first products, solid-state rectifiers. Of course, the company became a household name thanks to its loudspeakers, and in Japan there is no other loudspeaker worth considering!

From a hi-fi point of view, it's the 'Dual Concentric unit, introduced in 1946, that made the company's name. The combination of a high-frequency pressure unit firing through the centre of a large bass cone wasn't exactly a brand new idea, nor is it a device unique to Tannoy; Altec's famous 604 operates on a similar principle. What marks the Tannoy unit out is its refinement, which left the rest of the field sounding coarse, crude and industrial by comparison.

High-frequency pressure units work by compressing the air behind a phase plug and forcing sound down a small HF horn. At high frequencies, the wavelength of the sound coming off the itself, at which point cancellation sets in, hence the need for a phase plug.

To say the design of the plug is a little critical would be a major understatement; it makes or breaks the loudspeaker. Tannoy's early design is excellent. It was christened the 'pepper pot' after the small holes drilled from the 'back' of the plug. These merge at the 'front' to form the throat of the horn, thus ensuring smooth transition from phase plug to horn.

This is one of the single most complicated casting/machining jobs you can imagine. Tannoy couldn't afford to make this part anymore, even if they really wanted too, and have moved on to the Tulip Wave-guide with their more recent models. I don't feel this new system is quite as good as the old, but neither system is absolutely perfect, so it's probably six of one and half a dozen of the other.

The other trick Tannoy's clever designers engineered into the system was to make sure that at the crossover frequency (1 kHz), the pressure unit and bass cone are exactly half a wavelength apart. Therefore, by connecting the HF unit out of phase with the bass unit, the sound emanating from the system as a whole is in near-perfect phase, no matter what axis you listen on. No other multi-way loudspeaker manages this very important point so well; the Tannoy Dual Concentric is a genuine point-source driver.

COLOURFUL HISTORY
Early units made from the late Forties and on through most of the Fifties have been nick-named Silvers. This refers to the colour of the magnet cover (or, more accurately t~r the Silver, the cover on the magnet and pressure unit). These variants came in 1 2in. and 1 5in. chassis sizes, had separate crossovers and are now very rare indeed. Power handling is low by modern standards at 15-25watts, and impedance high at 1 50hms. A version of this unit was made for Pye and their HF25 loudspeaker.

Later refinements saw a change from Silver to Red, which brought with it a new cone surround and a hammerite-red magnet cover. I personally have not noticed any sonic difference between these two eras of Tannoys, but that doesn't stop the earlier Silvers fetching higher prices! Still, you are rather more likely to come across a pair of Golds, made from the late Sixties up to 1974, or the unpopular HPD series (High Performance Dual).

There is little that separates the Golds and earlier units sonically, but again, myth and legend dictate that the Silvers and Red are somehow superior. In my experience, the Golds need to be driven harder than their ancestors to get them to perform, but this is pretty marginal, and could just reflect the state of the particular drivers I was listening to.

Notable changes for the Gold included a change to 80hms for the impedance (to help transistors out) and user-adjustable HF Energy and Roll Off controls. Power handling also rose to 30watts for the 1 2in. and 50watts for the 1 5in. By the way, the first Golds do not have crossover controls and their plastic magnet cover is actually pink.

Introduced with the Golds was the little IIILZ unit. Although barely smaller than a 1 2in. Monitor Gold, it could be used in a much lower volume cabinet and gave sound quality just as good as its two big brothers. Strangely, this unit has a slightly larger HF diaphragm, perhaps in an attempt to reduce distortion.
 
 

PUTTING ON WEIGHT
By 1974, Tannoy were struggling to produce a high-power unit. 70% of the world's recording studios used Tannoys for monitoring at that time, but the growth in electronic music and transistor power amplifiers led Tannoy to rework the range and introduce the HPDs. Basically, they made the cone heavier by adding 'petals' to its rear.

Tannoy said this was done to cut down on cone flex, but it handily shaved a dB or two off the efficiency figures and increased power handling for a 15in. to 80watts. Sadly, in common with some of the late Golds, Tannoy decided to move from a plastic-impregnated fibre surround to a purely synthetic- foam one as well; after 25 years, you can imagine the rotten state these are going to be in, unless you're very lucky.

HPDs are pretty good but they sound a bit lifeless in comparison to their predecessors. All Tannoys up to and including the HPDs used Alnico ring magnets (common to both treble and bass drivers), while later units relied on ceramic.

If you've got a set of drivers, there's a bewildering variety of cabinets to bolt them into. At the top of the range is the Guy R. Fountain Autograph, at the bottom the bookshelf IIILZ. It has to be said that attempts to shrink the cabinets of later models didn't work too well - both the 12in. and 15in. need massive enclosures to function correctly, and in these days of stereo, not many people would put up with a pair of such huge loudspeakers in their front room.

Other than the models listed above, there were several 'professional' cabinet makers who constructed their own versions of Tannoy's enclosures, the most well-known being
Lockwood. Most of these non-Tannoys tend to be bigger and ugly, but sound fine.

Sound-wise all of these loudspeakers possess a big, clear sound. If you had to split hairs, then you might say the high treble can be a little 'tizzy', and the cabinets have a massive effect on the sound (just remember, the bigger the better!)

I have not mentioned tweaks on old Tannoys. As far as the units and crossovers are concerned, they should be left alone. However, it is worth bypassing the level controls on Golds and HPDs, as these do dull the sound. Some people rebuild the crossover with new components, but be very careful here as you will reduce the value of your Tannoys. The best tweak for smaller enclosures is a larger enclosure! Chatsworth and Lancaster owners in particular take note.

BOXED IN
What follows is a potted guide to cabinets up to 1974. Solid metal badges usually indicate Silver or Red units, plastic badges Golds (except for those in GRF and Autograph cabinets, which always had metal badges). Corner unit width is quoted at the widest point, and depth is front to corner-back.
 
 

	IIILZ 15in. (h) by 23in. (w) by 9 5/8in. (d). Invariably loaded with Monitor Golds. Great little infinite-baffle  speaker, 99.9% of the time in Teak. Sounds best close to walls on substantial 24in. stands. Pay around £200 for a good, clean pair.
	CHATSWORTH Two versions, corner - 39 in. (h) by 19in. (w) by 12in. (d) - and rectangular. Takes 12in. units and you'll find Reds, Golds and the odd Silver. Built late Fifties to late Sixties. Corner unit works better than rectangular on small stands about 1Oin. to 12in. high. Early models have little wooden legs, later versions a small plinth. Very good infinite-baffle loudspeaker. Pay £200--£300 for a pair, depending on Red or Gold drivers. Singles, £75-£100.
	LANCASTER Two versions, corner - 33in. (h) by 24in. (w) by 16 1/2in. (d) - and rectangular 33in. (h) by 21 1/2in. (w) by 121/2in. (d) Takes both 12in. and 15in. units, 95% Golds. 12in. is a reflex enclosure, 15in. an infinite baffle. Good sound, but the poorest of the lot, and the most common! 15in. rectangular sounds very compressed, with one-note bass; prefers small rooms with a 12in. Prices for the 15in. Tannoys did go mad at one point; thankfully they have come down quite a bit in recent times. Pay £200-£300 with 12in., and up to £500 for 15in. (slightly more for Reds). Rare as single cabinets, usually paired up. Cabinets are worthless really - these prices are mostly for the units themselves.
	CANTERBURY 37in. (h) by 25in. (w) by 17in. (d) Larger dual-port reflex corner unit, lovely Fifties radiogram look! Silvers or Reds normally fitted. These are rare but beautiful loudspeakers. Superb sound - open, dynamic, glorious. Budget on £250 for a single, twice that for a pair (hard to pair up though).
	LANDSDOWN 32in. (h) by 36in. (w) by 17(d) Silver or Red drivers. Oddity; large, imposing thing that doesn't sit well in a room, and the unit is positioned too low. Very, very rare - leave them for the collectors. First model Tannoy designed trying to avoid the use of a corner, but this back-fired. Worth about as much as a Lancaster in my opinion.
	YORK Early version: 45 1/2in. (h) by 32in. (w) by 22 1/2in. (d) Red, Silver or Gold. Large dual-port reflex corner enclosure designed for 15in. drivers. Big brother to the Canterbury. Totaly superb. This is pretty much the ideal enclosure for 15inches. Hard to find, so you will pay £800 up for a pair. YORK Late version Rectangular, single-port reflex with Golds. Looks like a bigger Lancaster, has a great sound. In demand, so £500 to £800 is the going rate.
	G.R.F. 46in. (h) by 40in. (w) by 23 1/2in. (d) Quasi-horn for corners, which will handle Silvers, Reds or Golds. Simply awesome. I once owned a pair but had to sell them to buy a house! I should have rented instead. Effortless bass, just glorious. Not as rare as you would think, either. £1200 to £2000.0 will buy a pair. G.R.F. Rectangular 42 1/2in. (h) by 23 1/2in. (w) by 19 1/2 (d) Liable to be Gold drivers. Compromised version of the above, but still excellent. Rare, but commands same price as above.
	G.R.F. Autograph 58 1/2in. (h) by 43in. (w) by 26 1/2 (d) Silvers, Reds or Golds. Goes beyond the G.R.F. by having a larger overall bass horn and a horn in front of the main unit as well. More efficient, more of everything. The only set I ever heard was in Japan, with matching ultra-rare GRF amplifiers. I was very jealous! 'Rare' is not quite the right word for either amps or 'speakers! Simply priceless, Tannoy did not make many of these brutes.

ONE CAREFUL OWNER

Some spares are still available from Tannoy, and considering the immense cost of the units new, they are quite reasonable. Bass cones blow before the HF pressure units do, and getting an original cone for a Silver or Red is now impossible. Later Golds and all HPDs suffer from surround rot, so tread with great care here; you can be certain the cone will need to be replaced. The later magnet covers on Golds are plastic and easily broken too. Beware missing magnet covers, as it can make it difficult for the uninitiated to tell one driver from another and doesn't do their value any favours.

Tannoy have survived the past 67 years and an American take-over, a management buy-out and the relocation of the entire factory from West Norwood, London to Glasgow. The reputation the company has world-wide is astounding, especially in the Far East where Tannoy is 'the' cult 'speaker
system. Throughout the late Seventies and on into the present day, outfits exist who have done nothing but ship older Tannoys across to Japan. This had forced prices up, but thanks to the current strong pound, now is the time to buy yourself a pair of Tannoys and enjoy!