Sunday, 29 June 2014

The Tannoy 15'' Dipole Enclosure – The Evaluation of the Known I

Hello to everybody,

interested into my Tannoy enclosures. In the last three to four month I did cover several articles about different Line Magnetic sets, assembled from LM22A, LM555W and LM597. I started the successful line from my conviction, that this horn array completed with dipole enclosure for the low frequency support, is one of the best speakers I have ever listened to.  I will cover more articles in future about similar audio chains, but it depends as well on the occasion of access to them. Through the evaluation of Mikes and Hans sets, it got manifested that the electronic components carry a remarkable part at the final aural result, in a way of execution, the owners didn't believe before. As already extensively reported, such a horn array, driven by a Shindo tube amplification chain, together with dedicated transformers, generators and other components, can work in a stage of harmonic holographic audio transparency, which I do not know a second time. It can, – it is not a inevitable result with such components or a result of other possibles recipes, it needs the educated ear of the holder to make it real.

In the past three years the described carefull setting up of both chains had a tremendous influence to the decisions about the design features of my enclosures. This decisions have been made about the acoustic principle of the enclosure type (dipole), the radiated wave front (front loading) and the general audible preferences (materials used). As already widely covered in my former articles about the enclosures, without the experience of the LM-set up, I never would have been able to realize the cabinets with such a incredible success. The physical performance of such huge medium frequency horns like the LM22A, covering a tremendous part of the frequency range (300 to 6000 hz) in combination with a dipole for the low frequency support, have given me a true new perspective what a loudspeaker is able to perform at its best. So I accepted some major changes during realization of my 15'' Tannoy enclosures and got rewarded with the by far best response I have ever listened to with Tannoy speakers.

But it has to be said as well that under permanent real impression of the LMs, with such advanced perfection of a almost holographic sound stage, together with all other favored properties, like harmonic micro detail, fastness and general naturalness, the Line Magnetic horns have created in a sustained way my precisely defined sense for the performance of such a audio transducer. Every time back home the listening to my Tannoys was a quite difficult experience with lots of aftermath work. It came several times to a point where it was hard for me still to believe into the unique properties of a 15'' paper cone speaker, covering the important frequency range of 1000 hz, like my Tannoy Monitor Red. I did hardly question the listenable results and the staging of my personal chain and its ability to follow on the described route in direction to a similar result close to the LMs. At the beginning I made the mistake to require the absolute same physical performance from my speakers and their driving chain. In the early stage of comparison I was not able to admit my set a own physical performance, with own peculiarities and unique individual qualities. I wanted it to perform similar to the bespoke LM set up. Of course I do know that this is in fact absolutely impossible, but my ear forced me to follow on… Comparing a 2'' aluminum diaphragm with a 15'' paper cone at the execution of middle frequency response is like comparing a truck with a sports car. This comparison would get better, if the mass of the cone will be reduced, may be to a third like with a Altec 755 full range speaker. Still this mass of the cone is several times higher, comparing it with the 2' aluminum diaphragm. Both cone masses create their individual conditions, which need to be featured and compensated by the driving electronics. Both cones create their own typical fluent rich tonality in particular with the important medium frequency response. Since the small mass of the aluminum diaphragm needs less driving energy and control, but it can tend to sound to thin or very technical, since the large heavy cones need some sort of the opposite compensation. One reason why the typical full bodied sound of the direct heated Western Electric 300b tube matches perfectly the demands of the Line Magnetic 22A metal horn. A perfect team mate.

For me it was as well a chance for perfect evaluation of my own components, their particular abilities and their competence to operate in a foremost natural inconspicuously way. Since I never could work out the level of experience like the ingenious mastermind of a Ken Shindo, who was able to conduct every audio component to a perfect match of his personally favored attitudes. I have to proof and readjust every amplification stage for its individual input of peculiarities. All my components got verified over decades and matched together to work in a good evaluated balanced mode. With my new speakers everything needed to be checked again, their new profound abilities made a advanced sort of coupling to a higher degree of definition necessary. During that time it came to a point where somebody offered my a LM22A/555W set as part of a attractive deal. It was a really hard test mode for me at that time, but I decided to stay on with my Tannoys, even if I did know that the final result can not be the same. I still believe into the unique properties of my enclosure design as a rare alternative option for the few Tannoy users, which want to get a speaker of highest expectation and refined expression. A speaker which can leave classic original Tannoy concepts far beyond, if naturalness, musical involvement and perfect refinement are the most sought qualities instead of superficial hifi attitudes.

My phono stage works on its own with extremely liquid naturalness, lots of harmonic detail and very refined overall tonality with quite good outer dynamics are the major qualities. I do use this design (5691 SRPP to 5691 OP, tube rectified and regulated PSU), since 10 years. It works in every respect and discipline better than anything I could compare it with, and this was a whole lot of commercially made tube phono stages. Big names, tremendous amounts of money, clever designs have been in comparison, I decided always sound wise, – but I did it with different sets and rooms with different speakers! Sometimes if one of the surrounding parameters is in minimal change, it might be necessary to check such decisions again. This phono amplifier had always some sort of a more self evident attitude than other options, – rounder with deeper insight into the musical fluid – with one word more natural sounding than others. I did built this type in the late 1990ties as a typical test approach after lots of discarded designs. It is very ugly realized from a US-military speech amp for the enclosure, the PSU transformers and the sockets, the amplification design is built up on a Kondo M7, but I did incorporate my beloved 5691 RCA red base tubes, a high mu equivalent to 6SL7 designs with unbelievable better sound properties, as a result of their sturdy mechanical construction. Till today I do not know a better sounding tube in the first stage of amplification of phono equalizers, the prices for them always have been very high, but with the web they have skyrocketed to the top of their range.

After this phono amp I did try again several other concepts, with inductive elements for equalization, different tubes in completely different arranged concepts, I always came back to that provisionally built sample shown in the image with the idea in mind: one day I will do a perfect made phono stage. Till today it did not happen.
For my actual evaluation the RIAA filter of my phono amp needed to be checked at a professional work bench, I never did that before, but I had the feeling that my low frequency filter gave me a bit to much punch. The filter was realized completely with paper-in-oil-caps and everybody with some experience in RIAA designs knows exactly what I want to say. High tolerances versus unique sound properties are in question with oil caps of such small values, in former years the exactness of the RIAA was not my foremost trial, I spend much more energy to get it singing in general, to difference out, if it is more tenor than baritone was not my major aim. But now it needed to be evaluated a bit more precisely. My friend Klaus has well equipped test bench with uncountable W&G components for every reason, so it came out that I had a good mismatch in my RIAA filter by typical 10% variants of caps. After selecting pio caps for better matched values, I got my filter into a less than 1% tolerance, which is very good comparing it to the variations pressed into the vintage records. The first active amplifying stage in a chain has a tremendous impact to the final result, every little detail which gets here included in perfect shape will bpassed through the coming stages with audible success. So I still cannot accept anything else than oil caps for the RIAA filter, even if its getting really difficult to match.

My line stage pushes the general performance towards a highly transparent holographic audio image. In combination with a unknown spectrum of musical harmonies and rich open dynamics it shows all the very typical attributes of Directly Heated Triodes. The holographic attributes of my line stage make it a perfect companion for compensation assignments in the important medium frequencies, when a huge paper cone speakers will be the transducing element. Directly Heated Triodes with thoriated tungsten filaments are in small signal amplification stages a unbelievable formng element. By far more important than incorporated as power tubes. It can not be said enough, in earlier stages their same aural benefits are much more effective shown. My line stage uses the Aa Weitverkehrsröhre, one of the most holographic sounding tubes money can buy. But…, if there will be not their "archilles heel", the high internal impedance (Ri), which makes the use of this tube a bit tricky. As a result its output impedance is quite high and it will not be a universal match for any tube amplifier at planet earth, transformer coupling is impossible, shortest connections are a must to get them work best.

Finally I do use the well known Leak TL12 Point One power amplifiers, since these a simply one of the best tube amplifiers made ever. They are early push pull designs, with all positive and negative attributes such a (Williamson derivate) principle offers. Push pull designs emphasize at the frequency extremes, but as well are characterized to have by far a better control about speakers, with 15'' paper cones this can be a very sophisticated property smaller speakers don't need. More common push pull  examples from other brands are mainly characterized with thin tonality and limited middle frequency response. Leak did a time typical oversizing of their transformer designs, together with a relying on oil caps in all sections make this mono amp a major design in history and they are as well highly sought after. These early Leak models (1949) cover the rare and important skill to keep the musical content in a comprehensible flow, a attitude which only a handful of brands have been able to perform, – independent of the virtues of push pull or other design strategies. Their extremely complex output transformer design (Haddon) with 8 independent inlayed coils at the secondary, typical (2, 4, 8, 16, 32 ohms) for all early Williamson designs, may be as well responsible for their elaborated and refined performance, which any other later Leak model could not hold. A complex extra benefit which has been given up first in the early 1950ties as a result of already cost cutting issues tamed to growing productions figures of a beginning audio market.

I do know my chain very well, after readjustment of my RIAA the whole set works with a remarkable similarity to both described Line Magnetic sets. It works with minimal lower resolution in the important frequency range between 500 to 1500 hz. Of course the resolution of a 15'' paper cone can not show the same attitudes like a big horn development driven by a small diaphragm of minimal mass. But the overall insight into the music, the dynamic abilities, as well the eminent importance of micro dynamic detail of higher frequencies is extremely similar throughout the front loading and the dipole principle. Listening to them just leads to forget about other sets like Line Magnetic, they can induct their listener in a way only a few speakers are able to. A benefit of the 15'' Tannoy Monitor Red Dual Concentric speaker is its perfectly match of high and low frequency timing, as a result of physical perfectly arranged coupled units. Here the long horn development of the LM22A creates a profound difficulty, but it can be perfectly reached and even better without digital support.

Read on soon about my future tries of integration of completely different amplification concepts like a 300b amp, which will change completely the sound structure again,