Fostex NF-1, Technical White Paper

Page: 9 / 16

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enhancing the bonding strength of all materials, and
subsequently, substantially improving resistance to
humidity. These materials, being equivalent to the
coating applied on the famed Stradivarius violins,
help give the feeling of being present in a natural
sound field and reproduce the true sound of musical
instruments in higher fidelity.
Previously used olefin-based PP materials caused
strength to fluctuate greatly depending on the
temperature. This means that changes in room
temperature and rise in the voice coil temperature,
when driven, will result in considerable changes in
sound quality. They are fated to be a source of
changes in sound quality due to seasonal
temperature changes.
The woofer found in NF-1 is the incomparably
successful compilation of our 50-year long research
and development efforts for elementary
technologies in wood pulp-based
diaphragms.
Physical properties of this new Biodyna are given
below:
3) HP diaphragm adapter
4) UDR tangential edge
When speakers are driven, the roll of edges
(surrounds) plays a major part as the suspending
member. They, as part of diaphragm systems, are
also greatly responsible for the reproduced sound
quality.
This fact makes it essential to be most careful
when designing edges, where more points of
difficulty than in diaphragms are involved, when
deciding on configuration and materials.
What we chose for this project are special
urethane foam materials having greater internal
loss and elongation performance, as well as
excellent durability. They are a breakthrough of a
newly developed structure called a UDR
tangential edge, on which up-roll and down-roll
are bonded at their tangential surfaces. They are
configured, through FEM modal analyses, to
function optimally as edges. Targets set at that
time include:
Reduction in anti-resonance at mid-
frequencies:
No previous rolled edges were without anti-
resonance. The voice coils we adopted are
structured
tangentially to
voice coil
movement.
Freedom from
axis-symmetry
anti-resonance
caused by
movement of the
outer periphery of
cones and inner
periphery of rolls
in the mutually
reversed direction
produces flat
response and
reduces harmonic
distortions to an
absolutely
minimal level.
Drive points of HP diaphragms can seriously impact
characteristics. However, analyses using computers
and subsequent technical experiments have
discovered that the high end will be extended and
directivity improved if driven near the center. For
the woofer being discussed now, we chose a point at
about 25 mm as the optimum performance point.
As a consequence, the network
coil for the woofer became
superfluous without loss of
smooth transition to the
tweeter.
When determining the blending detail not to miss a
single piece of the subtlest signal components in
reproduced sound, a greater amount of attention to
propagation velocity than to that of diaphragms was
paid.
Density:
Young's modulus:
Propagation velocity:
Internal loss:
Modulus of flexural rigidity (
√
E/
ρ
3
):
Propagation velocity X Modulus of
flexural rigidity:
Supported by high level strength and large internal
loss, which were attained for the first time, and by
the use of a strong magnetic circuit and rigid die-
cast aluminum frame, superior sound quality with
high transiency and linearity, which had not been
available from any speakers, became a reality.
0.64 (g/cm
3
)
11.02 (GPa)
4380 m/sec.
0.068
6.5
26.98 X 10
3