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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 Nd
2
Fe
14
B magnet Tc is equal to 319 °C.
Which means, should the magnet reach its Tc, the magnetic stru cture 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-JMlab patent
pending. The material used in the magnet is Samarium-Cobalt Sm
2
Co
17
, 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
“Power Flower
™
” - a patent for a high precision mid-range
The new mid-range 165mm driver has also directly benefited from Focal-JMlab’s experience of
developing Cone “W” technology since 1995. A new membrane has been developed for use with a
new a 40mm coil and the optimisation of its rigidity has allowed a “single skin” cone to be formed,
which is perfectly controlled over a one octave range from 1 500-3 000Hz - essential to the setting
of the OPC filter. The phase plug is no longer effective and is replaced by a large aluminium focus
plug. Any risk of coloration is eliminated and directivity is optimal. The link with the tweeter can
be made seemless and the impusle response of the combined tweeter/mid-range is ideal.
This mechanical optimization of the drivers eliminates the source of various sonic problems and
in addition offers the guarantee of great manufacturing consistency. The magnetic circuit must
be of high precision with very low losses. But the utilisation of large pole parts generates a problem
of flatness. The bonding beetween pole piece and magnet is not consistent and generate magnetic
losses. The “multiferrites”, technology, first initiated by Focal-JMlab more than twenty years ago for
the company’s top woofer , also brings an unexpected solution to the mid range of the Beryllium
Utopia line. The new - patent pending - “Power Flower
™
”, uses seven powerful, but small diameter
ferrites laid out concentrically around the core. Bonding beetween pole piece and ferrites is very
accurate and cancel any variations due to small deviation in the flat surface. Moreover the polar
parts are machined in the shape of flower, whose petals match the shape of the ferrites, and to stop
magnetic escapes between the bottom and top of the field. Finally, this arrangement satisfies a
double requirement: high power output and perfect control of the magnetic discharge. Magnetic
loses in production are thus very small and in combination with the tight tolerances of the Cone
“W” manufacturing, the “Power Flower
™
”* design has given exceptional accuracy to the 165mm
mid range unit. The very small tolerances ensure a perfect reproduction of any performances,
particularly in the highly sensitive mid-range, guaranteeing the strict tonal balance of the speaker.
Being hidden away magnetic circuits are seldom considered. However the energy
that they give is essential to the quality of reproduction. Focal-JMlab is always asso-
ciated with investing in powerful arrays. And with the new Utopia line, the com-
pany wanted to apply its latest innovations.
* The concept of “Power Flower
™
” also offers two additional advantages of excellent coiling for the coil
and offers two another advantages, an excellent cooling of the reel and a full back de compression.
The new mid-range “Power Flower
™
”. A great manufacturing consistency
provides an exceptionnal accuracy to this 165mm, guaranteeing the strict
tonal balance of the speaker.
The shape optimisation and the use of multiferrites reduce consistently the
magnetic field losses.
"Curie Point" of different magnets. Only Samarium-Cobalt and Alnico offer
a large safety area when temperature increases.
"Focus Ring
™
" : Neodynium ring concentrates the magnetic flux to 2T.
The central magnet uses Samarium-Cobalt to offer high stability with
temperature.
5
Focus Ring
™
and Power Flower
™
User manual Utopia Be line
notice utopia be 5 19/04/04, 15:32:42