Article taken from Haute Fidélité, January 2002
TECHNIQUE
ENCEINTES OCELLIA KEDROS 2 SILVER Figure
libre 
Acoustique et Lutherie has been offering for about three years a completely original approach, applying to speakers techniques similar to the ones of musical instruments. The idea is easy to understand, but if it’s rarely implemented, it’s because it’s extremely demanding. A speaker made according to this principle can’t be elaborated at a table corner or even with a computer. It requires a long adjustment, in which the musical culture of the creator plays a dominating role. As a matter of fact, in order to create speakers like the Kedros, you need to be able to lead a long empirical process that consists in trying solutions and judge the result listening to it, and therefore get to an optimal solution, which is not easy to define on a paper.This is a little game amateurs who spend their weekends perfecting big fixed up systems enjoy doing, but it’s more difficult to insert in the rational and economical context of a firm that needs to always make profit of the money it devotes to create and test a pile of prototypes. Here are in a few words the principles according to which lies the conception of the Ocellia in general, and the Kedros in particular. The parasitic vibrations of the cabinet are one of the main problems every speaker maker has to face. A big majority of them fights the problem focusing on the vibrations: The speakers are made with heavy and stiff sides and they are stuffed with deadenning materials. The inconvenients are they tense the sides, they move the sound modulations higher, in the areas of the spectrum they finally bother more, the accumulation of deadenning materials ends deadenning the music itself, and the increased weight of the whole thing increases the quantity of energy the speaker is able to stock and restitute illadvisedly. The main originality of the Ocellia speakers lies in the way of managing these vibrations: instead of increasing the weight of the speaker, it is lightened so that it stocks a minimum of delayed energy. The little remaining energy won’t be muffled at all price but used so that the cabinet sounds in a harmonious way. Here is what leads us to the firm name that makes the Ocellia: Acoustique et Lutherie. The way they make the Ocellia links them to the stringed instruments, in which a box reinforces and enriches the sound produced by rubbed or plucked strings. The difference between the Kedros and the other speakers in trade is not only a concept: it can be seen and felt. First, the speaker is extremely light. In fact, almost all the weight is in the loud speaker which is, for its part, very heavy. We have the feeling the rest doesn’t weight anything. As a matter of fact, the sides of the speaker made with spruce pannels ( the same wood which is used to make music instruments ) are extremely thin ( 4 mm ). On the contrary, the peripherical structure and also the superior side of the speaker ( in beech ) are stiff but without an excess of weigh as the whole thing remains very light. There are also numerous strengthening pieces that can remind the role of the soundpost in the stringed instruments. Finally, the Kedros don’t have any “ floor” and are generously ventilated with three spouts situated at the basis of the speaker: two of them on the sides and one on the back with an adjustable flap to adapt the sound equilibrium of the speakers to the room, to the rest of the listening system and to the taste of the listener. The size of these openings lets think that the cabinet works more as a folded up open baffle than as a closed speaker or even bass reflex. Finally, but this is more classical, the speaker is not a perfect parallelpiped to avoid the making of stationary sound waves: the front face is lightly inclined and the lateral walls go spreading backward. The top is horizontal, but as there is no floor, there is finally no parallel wall. The quality of the cabinet work is finally exceptional: the wood is magnificient, the assembling perfectly adjusted, the sanding minutious, and the varnish perfect ( it is a varnish that can be compared with the ones instrument makers use ). This so particular cabinet will definitely have a very original behaviour toward the music produced by the loud speaker: it will vibrate more, for certain. We can experience it when we put the hand on top of it. But it doesn’t vibrate as long ( thanks to its lightness ), and the vibrations, better distributed on the frequency response, makes an equilibrate unity with the direct sounds emitted by the loud speakers. The last characteristic, that illustrates very well the exceptional nature of the Kedros is that the  cabinet doesn’t integrate any damping. You have read it right: there is no damping at all. This is possible because the words, the glues, the assemblings, the strenghtenings, the shape, the varnish, and of course the high speaker, everything has been conceived, tried and made so that the music sounds beautiful. So, as a result, there is no need of damping. And you can hear it, because the damping doesn’t only muffle injurious resonnances. It merely muffles music. An Ocellia speaker is thus an entirely different philosophy: the speakers participate to the music whereas with all the other makers, it is only a passive object with which one only tries to limitate the defects, considered as unavoidable. The high speaker chosen by Acoustique & Lutherie for the Kedros is not the first one chosen either. It is the 30 cm coaxial by Phy-HP. It’s probably the most expensive high speaker of the market. This is not a quality by itself but it can give you an idea of the level of ambition of the Kedros. It is a totally unique product, that unites a 30 wide band with a piezoelectric tweeter placed in a coaxial position. This is so original that one could think its maker tried to find originality at any price. In fact, everything is linked together in a very original way: Phy-HP has always made the choice of a wide band and the first model, a 21 cm has been conceived to work by itself. On a philosophical point of view, the choice of a wide band is quite clear with the spirit that took part in the conception of the Kedros. Making a wide band is extremely difficult, but when it works, what a marvellous music ! Shifting to a 30 cm allows to nicely increase the level in the low pitched, but it’s more difficult to increase in the high pitched with a membrane of that size. Therefore the necessity to add a tweeter. Unfortunately, the union of a tweeter with a wide band is one of the most horrible brain teasers of the Hi-fi history. As a matter of fact, the wide bands generally have a very high impedance in the high pitched ( the one of the Phy raises up to 30 Ohms), so that the connecting up of an ordinary tweeter with an impedance of about 8 Ohms, even if it’s strongly filtered, ends bypassing the wide band and destroying all its qualities, as if it was filtered itself. The advantage of the piezoelectric tweeter is that its impedance is of about 100 Ohms at the basis. So the union is possible. Like every Phy high speakers, the coaxial 30 cm is a very traditional product, in its best meaning. It could have been made this way half a century ago because it doesn’t contain any technological innovation at all: a basket in bronze, a non treated paper membrane with a little folded up suspension, an overpowerful magnet in Alnico, a very narrow air gap, a silver wired voice coil, isolated with silk ( this last point being a new one that appeared on the recent models ). Each element taken separately doesn’t present any originality nor any major innovation, but this loud speaker has concentrated all the know-how accumulated in the field of wide band by all the makers in the world for fifty years and more, and finally it has absolutely no competitor. The 30 cm is set in the speaker without any filter, as a definition, the filter of the tweeter being integrated in the loud speaker itself. By the way, this is a rather surprising vision to see the cables coming directly from the terminals to the loud speaker. The wiring is made with Phy-HP cable, a strong section copper monowire, silver plated with a cotton covered isolation. The terminals, with 4 pins to allow the bi-wiring is plated silver. It only accepts banana pins. The finish can be adapted to the demand as far as the varnish colouring is concerned. As it is an instrument varnish, the Kedros can logically take all the colours the instruments can have: from the natural wood colour ( which is nicely golden ) to the reds and dark browns we can see in all the orchestras. The global sizes, without being very discreet, still remain acceptable to be put in a music lover’s living room who would be ready, by definition, to consacrate to the music an important place in his life, in the literal and figurative meaning.
The listening This listening had a particular meaning because owning for three years a pair of Phy HP 30 cm coaxial loud speakers, I have put them in boxes made on radically opposed principles, to the ones that have managed the conception of the Kedros. As a matter of fact, these boxes are made with a plywood sandwich ( plumbed tar ) an extremely heavy plywood, and they are filled with all sorts of damping. At first, the arrival of a speaker that also goes against this assembly had everything to surprise us. In fact, I’ve had to recognize with humility there is an audible difference ( and it’s a euphemism ) between my personnal do it myself and these speakers made according to the rule book by true professionals. And the pleasure I have felt from this listening has largely compensated for this little self-esteem wound. The listeners used to more ordinary products are generally disconcerted, at the first listening, by speakers like the Kedros. They say things like “ There is no low pitched “ or “ There is no high pitched “ . Above all, they mustn’t give up after this first feeling. In fact, it only reflects the difference in philosophy and ambition that separates the Kedros from the rest of the production. Let’s take the problem from another point of view. After a listening with the first pair of cables I could catch, the Hi-fi chief editor suggests another cable that, according to him, should give better results. I’ve always been very skeptical on the influence of cables on a listening system, but then, I was astonished : There was nothing to do with the other ! As if the system had been completely changed. So there is at least an evidence: The Kedros are “ transparent “. The smallest change in the elements upstream can be heared. The inevitable consequence is that: They are extremely sensitive to the quality of the associated electronics. As consequently they are no demanding at all as far as power is concerned ( high efficiency and high impedance: a piece of cake for the amplifiers ! ), the triods will,of course, be perfect, but the tubes in general and the little transistor amplifiers, judiciously chosen, can also be suitable. By the way, this transparence should make think those who keep speaking about the high and the low pitched! Isn’t the Kedros transparence the direct consequence of the fact they don’t add any high or low pitched ? In fact, there is some low pitched, even a lot of it if the record is filled with it. You only need to feel the huge fullness of the sound scene when the music is recorded in a church or in a big concert hall. And the high pitched is really present, but it’s so well integrated it cannot be “heard”. When we look for it , we can’t isolate it, and this is so uncommon in Hi fi we can hardly get used to it. Some listeners will even feel frustrated : This is true that listening to a clearly voiced high pitched can be considered as a pleasure of Hi fi. But does the music take advantage of it ? Those who are used to it at the concert know it is not the case, and they will recognize in the sound of the Kedros one of the most perfect imitations of the concert they can find in the shape of a finished product available in trade. The two fields in which these speakers out of the common pleased me the most are the carnal truth of the timbers and the realism of the sound scene. The timbers have an extraordinary consistance, with an astonishing “material” side: We can really hear the wood, the hair, the metal, and not mere notes. Throughout that, the Kedros come near the best big bell systems, much more cumbersome, and you will not find them as they are in trade. With both their fullness and the realism of the sound scene, the Kedros create a gulf with a possible competitor. The musical scene spreads out with an astounding realism at the back of the speakers. When we close the eyes, the effect is striking, and when we open them again, we have the feeling we can see the wall of the room “fall” like a curtain on the musicians who were standing there just a few seconds ago. The quality of this sound space is deeply linked to the discreet high pitched. When the high pitched is too present, it remains “glued” to the tweeter and the tweeters are the ones that determine the position of sound sources, to the detriment of all depth. Olivier Corto | |
