Tannoy’s Cardioid ribbon microphones

As well as the bi-directional microphones described in my previous post, Tannoy also produced several cardioid models. In the picture below, the mic on the left is the MD422. I don’t have a model number for the centre and right hand microphones, but they are the same basic microphone inside, with very different grills and bodies.

The internal design of these two microphones is very simple, with a huge heavy horseshoe magnet providing both the magnetic field and creating an internal cavity to help control the pattern. The ribbon pole pieces are simple rectangular steel plates screwed into position.

There is a layer of felt behind the ribbon. I also expected to see the cavity behind the ribbon stuffed with horse-hair or cotton wadding, but in this example it was completely empty. There is a small transformer in the base of the microphone – in this example the output impedance was 2000 ohms, but I’m sure that other output options would have been available.

Despite the size, the output level is rather low.

I have already written about the Tannoy MD422 cardioid ribbon microphone in an earlier blog post so will try not to repeat myself too much. However,  this is one of the few Tannoy mics for which I can find a firm date, based on a BBC report from 1953. 

The MD422 uses the same ribbon motor as the Type 2 bidirectional mic, and we can safely assume that they were contemporary models.

As well as these large cardioid microphones, Tannoy also produced this smaller directional model which looks rather like a dynamic mic:

The motor inside this mic is reminiscent of that from the STC 4104 lip microphone. It uses the same base and connector as the MD422 and MR425 models.

Update March 8th 2015
Tannoy were developing directional ribbon microphones from the mid 1930s onwards. I have never seen this model on the bench, but this sketch appears in Wireless world in September 1937:

Tannoy and the Houses of Parliament

Tannoy ribbon microphones were used in the British Houses of Parliament. According to Chris McClean’s article for the Institute of Professional Sound, twelve ‘brass barrel’ microphones were fitted by Tannoy in 1951, and the system was further upgraded in the 1970s, again by Tannoy, with a system than lasted until 1991. 

Here’s the problem: I have seen several of these brass-barrel Tannoy mics on sale that claim to be ex-Parliament. Too many, certainly more than twelve, and some at very inflated prices. Either Parliament kept a huge number of spares (which is possible, I guess), or this model was not exclusive, and was sold elsewhere. I have heard anecdotally of these being salvaged from church PA systems, and also the Canadian government.

Additionally, I have seen, and bought, Type 3 bidirectional Tannoy mics that claimed to be ex-HOP., although when I asked for documentation as proof of the claim, the seller was unwilling or unable to do so. Were these fitted in the 1970’s refurbishment? Again, it is possible, but I have yet to see any proof of this claim. If you know better than please get in touch and show me!

The lesson here, as always, is Caveat Emptor, particularly when buying used microphones.

Update March 8th 2015
Thanks to one of our readers for sending in a link to this announcement in Tape Recording magazine (1962, issue 5). This adds to the Houses of Parliament microphone debate.

The article announces two new ‘Slendalyne’ ribbon microphones from Tannoy – a cardioid and a bidirectional version. Yet the cardioid version looks very much like the brass-barrel mic that was supposedly installed into the Houses of Parliament 11 years earlier! This sentence is particularly intriguing: ‘Although they have manufactured microphones for internal use before, this company has never made their instruments available to the public before‘. The statement is not quite true as their earlier models were widely available. But this implies that these specific models had previously been supplied to select customers, and became available widely from 1962 onwards.

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Thanks to Tom McCluskie, Jamie Neale of Real World Studios, and Marco van der Hoeven of Vintage Mic World, and everyone else for sharing information and photographs of their microphones.

This is my attempt to round up and discuss the various ribbon microphones that were made by Tannoy. I have split this survey across two posts, with part 1 describing Tannoy’s figure-8 microphones and part 2 focusing on their attempts at cardioid ribbons. Finding firm dates and model numbers is a little tricky as they are rarely marked on the microphones themselves, and so there is a certain amount of educated guesswork involved. If you know more, please get in touch!

Update 8th March 2015
Several kind and knowledgable readers have sent in links and articles with dates and model numbers. I have added these where possible. Thanks to all!

Figure-8 ribbon microphones

Over the years Tannoy produced three main models of bidirectional ribbon microphone, with some variations around those types. I have called these types 1, 2 and 3 in order of production.

Type 1
The BBC technical team reviewed this mic in 1947 and applied their usual exacting standards, rejecting the mic for broadcast use. But as usual the benchmark mic for comparison was the BBC Marconi AX model, which cost many times more, and in fact these mics can sound warm and rich, with an overtly vintage tone.

These mics are heavy with a cast body and large cylindrical magnet. I have come across mics with different output impedances, usually 50 ohms, 600 ohms or high impedance.

In response to the BBC comments, extensive changes were made to the motor design, although the body remained the same. The magnet structure is completely changed, with what looks to be a single cast magnet. I have never actually seen one of these on the bench, but Seth at the 2 Track Mind blog has written a nice post about his microphone here.

Type 2 – MR425
The Type 1 mic was succeeded by the type 2 or “Pitchfork” model, which is much smaller and has a completely new motor design. This model seems to date from the early 1950s and was available in different colours with different mounting options.

Update – this model has been identified as the MR425, and it was briefly mentioned in Wireless World in May 1952:

Type 3 – Slendalyne

These mics are smaller again and use a lot of plastic in the body, which can be prone to cracking. The grills are stamped metal, and the connector is a simple DIN plug without a locking ring. They are a lot less common than the types 1 and 2, although perhaps not as rare as has been suggested by some sellers.

The magnets in these mics are made from a ceramic material which allows a smaller, lighter microphone than its predecessors.

Update: This microphone has been identified as the Tannoy Slendalyne model which appeared in Wireless world in June 1962:

In my next post I will describe Tannoy’s cardioid ribbon mics.
Stay tuned!