Fostex NF-1, Technical White Paper

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5) Factors required of HP sound reflectors
Consistently varying third-order curved surfaces are
ideal to cause and maintain regularly diffused
reflection. For such curved surfaces to be realized,
nothing can be better than the HP structure.
Minimization of self-resonance inherent to
reflectors is also a requisite, for which a
configuration in which strength can be assured is an
important factor. The HP structure is also very well
suited in this sense.
Materials are to exhibit great strength and large
internal loss. To meet these requirements,
composite materials of carbon fibers and PBO,
compatible with those of diaphragms, are used.
6)New bass-reflex system
FEATURES OF NETWORKS AND CONNECTIONS
FEATURES OF NETWORKS AND CONNECTIONS
1) Network
The simpler the crossover networks for woofers and
tweeters, the better. An ultimate incarnation of this
formula, i.e., non-use of any network element, is a
reality with the woofer. The tweeter is connected
through a capacitor for a 6 dB/octave attenuation.
This achievement is possible simply because of
smooth roll-off of the woofer at the high end, which
no technologies other than the HP technology can
achieve.
The use of a high quality film capacitor and a 1.5
mm diameter solid wire is another factor for this
superb transition.
2) Bi-wiring
Successful achievement of our targets set for
NF-1 listed below requires use of a bi-wiring
system.
To attain dynamism and massiveness in base
response, bass-reflex enclosures are adopted.
With NF-1, acoustic conversion of extremely low
loss is achieved by the active utilization of
reverberant sound caused by the interior HP sound
reflector and exited through the bass-reflex ports.
For this, ports are located at two places between the
woofer and tweeter to allow for smooth and natural
blending of the sound exiting through said ports
with the sound coming directly from the drivers.
Figure 18 shows woofer response characteristics in
comparison with a glass wool case. It is obvious
from the figure that the sound pressure level is 2 dB
higher, assisted by utilization of sound created
behind the diaphragm.
Furthermore, bass reproduction capability at around
f
0
is 3 dB higher when an HP sound reflector is
used.
This has listeners perceive the sound to be very
rich, as if they are listening to a larger sized
speaker. As a matter of fact, the response curve
represents ideal characteristics.
Figur17shows a case where an HP reflector is located on 3
of the interior faces of the
enclosure. The use of the HP system permits time-
dependent attenuation to occur
gradually and consistently after a 10 m second period over
the entire sound spectrum.
Figure17
Figure18
20 50 100 200 500 1k 2k 5k 10k 20k
90
100
80
70
60
Hz
(dB)
Frequency responses with HP sound reflectors and glass wool
(woofer unit only)
With HP sound reflectors With glass wool