Being hidden away magnetic circuits are seldom considered. However the energy that they give is essential to the quality of reproduction.
Focal is always associated with investing in powerful arrays. And with the new Utopia line, the company wanted to apply its latest innovations.
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"Focus Ring™" - a patent for the magnetic circuit of the tweeter.
An intense magnetic field is of the utmost importance for good tweeter performance and the TGU conceived for large Utopia into 95 was a key point in the development of the Utopia line. Selecting a magnet that combines high power with small dimensions narrows the choice of magnet material to Neodymium.
However the small dimensions required - and the need for a light coil with a narrow air gap leads to intense heating of the magnet. A problem then occurs due to a characteristic of Neodymium: its low "Curie Point".
The magnetisation saturation decreases as the temperature rises and will cancel at a certain temperature, called the "Curie Point" (Tc). For a ferrite, Tc is equal to 450 ¡C and, for a Neodymium Nd2Fe14B magnet Tc is equal to 319 ¡C. Which means, should the magnet reach its Tc, the magnetic structure will loose its magnetism bringing irreversible damage to its output and an audible loss of dynamics and definition.
Since the design of the TGU in 95, the evolution of the home cinema arena has imposed new constraints with regards to power handling. In high fidelity musical performances very little energy is demanded at high frequencies.
However, with the special sound effects of home cinema new rules in terms of power handling are created, with the subsequent effect on magnet temperatures. Handling these new demands was a key rational in the design process of the new tweeter Beryllium Utopia (TBe), which adopted a key new concept called "Focus Ring™" - Focal patent pending.
The material used in the magnet is Samarium-Cobalt Sm2Co17, which is more expensive and slightly less powerful than Neodymium.
However it offers a major advantage in that it pushes the "Curie Point" (Tc) back to 825 ¡C, avoiding any chance of temperature related magnetic losses. However to obtain a magnetic field of 2 Tesla, as in the TGU, doping of the magnetic circuit is required by using a Neodymium ring to surround the Samarium magnet, thereby concentrating the magnetic flux and reaching the target field.
In addition, with the ring being mounted away from the coil it is not affected by temperature increases and gives the tweeter exceptional stability.
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