For
more than 15 years the composite cone sandwich technology
is a Focal-JMlab exclusivity. The W process, fi
rst initiated in 1995 with the Grande Utopia, provides
now a true optimisation of the frequency response.
Properties
of a drive unit membrane
Three parameters are of prime importance: mass,
internal damping and stiffness.
• Stiffness allows the cone to behave as a
piston over a wide range of frequencies, especially
important at bass frequencies for low distortion.
• Low mass delivers maximum acceleration on
transients for the best reproduction of fine detail.
• Internal Damping damps out any ringing or
vibrations in the cone structure that would otherwise
color the sound.
Materials
• Paper a light material, though not very
rigid, but with reasonable internal damping. Sound
often suffers from a “cardboard” coloration.
• Polypropylene/Plastics a material relatively
heavy, but with good internal damping properties.
Not especially stiff and the sound tends to lack
detail and precision.
• A simple woven aramid fibres cone (not a
sandwich type construction) uses a resin to seal
the cone and bring about the rigidity required,
but this tends to lead to a dull plastiky coloration.
The sandwich structure Focal-JMlab
During the mid 1980s, a new type of cone was developed
and patented by Focal-JMlab which combined low mass,
stiffness and high internal damping; the “Poly-K
sandwich”. Using woven aramid fibres tissue
skins and a core of hollow microspheres of glass
mixed with a resin, this structure exhibited extremely
high rigidity and low mass.
The damping could be controlled by the properties
of the core.
Since this original construction, the process has
been refined and developed to produce a new generation
of aramid fibres sandwich. The major advance in
the construction of this cone is the use of a special
structural foam in place of the resin + microballs.
This foam is used primarily in the Aerospace industry;
no other foam offers the same high ratio of stiffness/mass.
The name W is derived from Verre-Verre (Verre =
Glass). The W cone uses two very fine tissues of
woven glass that are lighter and thinner than aramid
fibres.
In addition, the molecular bond between the foam
and the glass tissue is far superior to that of
the aramid fibres. This results in a cone structure
which is mechanically more stable and with superior
stiffness. This construction allows us to further
optimize the transmission speed of the sound wave
in the cone. This new construction process allows
the amount of internal damping in the structure
to be very accurately controlled by varying the
thickness of the foam: the thicker the foam, the
higher the damping factor.
The relationship between the thickness of the glass
tissues and the foam core allows us to finely optimize
the cone structure depending on the particular application
and the frequency area to reproduce.
In 2003, a new W cone generation was born. Thanks
to glass veils of stronger density and foams available
in various thicknesses, the new manufacturing process
offers numerous solutions to sculpt the loudspeakers
characteristics at will.
The W cone produces an extremely transparent and
neutral sound free from coloration and distortions
normally associated with loudspeakers.
Its only limitation, the price; more than ten times
the price of a quality paper cone.
