Fostex FE168sigma compact bass-reflex

　　"16cm(6.5 inch) fullrange bass-reflex system has performance
as good as 20cm closed system." I thougt so vaguely listening to
the MFB20.

　As wide range fullrange units we remember Technics EAS16F20,
Fostex 168sigma,etc. Maestro Nagaoka had designed a huge bass-
reflex system "BS168", its specification is as follows.

　　Inner cavity 46 litter
　　Duct 99 cm^2 x 10 cm
　　fd 59Hz

　　
　　　　　　　　　　　　　　　frequency response(3m)

　　This is the frequency characteristics of BS168 measured by Nagaoka Tetsuo.

Please remember these words.

　Motional feed back or current positive feedback have these effects.

　　That is,

　　　Qc of cone will decrease and Qc of duct will increase.


　　Plain explanation
　　

1)When all are walls Qd will be maximum.
2)When a part of walls is cone Qd will decrease.
3)When cone is controlled by MFB, Qd will approuch to Qmax.

　　When MFB is applied, Qd will rise and small box may be enough.

　
　Well-designed 10cm full range system can reproduce all the notes
of rythm section. So it is very good for enjoyng music by brain.

　　On the other hand 20cm system adds richness to the sound,
it is good for enjoyng music by heart. And it must be.

　　If MFB is applied "fo resonance" will be eliminated and this
tributes to reproducing pure harmonization of orchestra.

　　Then how 16cm system is to be?.....Both !.

　　The reason why I don't began to craft for a long time is the price
of FE168sigma. It costs 10000yen for one unit. It's the same price as
JBL 16cm coaxial 2 way. So I hesitate to commit.

　　But it is a strong motive to want to listen to sound of pulp cone unit
with mighty magnetic circuit ( I've listened enough?).

　Now I could get these units at last ! I didn't purchase them ,
they came from a person who will give helping hand to this project,
for this project was too slow.

　Gorgeous casted frame and light pulp cone are characteristic.

　If I give some dimensions about the baffle, it is a finis. Because
this is typical bass-reflex design.

　　This is AST adaptor for HMA9500II. But it gets small noise.




　　Effect by this adaptor is great. The old familiar music source is full of echo.
Of course it is not because echo was added, but because resonnance was
substracted.

　It is so analytic as if the shape of echo is seen.

　Dimension was given by chance. After that, smaller part is calculated.
Why the first dimension was given? It is almost unacountable. But if it
is beautiful, it is best in most cases.

One fine day in the garden








　　Cut by 45 degrees.This method is simple and easy.

　　Design and construction






　　Inner cavity=294x202x206=12.2L

　　Ouch, it's a mistake!






　This scene is similar to violin craft.

　
Constructed !

　　Impedance(Bare unit)

　　fo=72Hz

　In a closed box

　　fc=105Hz


　　Duct diameter 3cm length 47mm(two ducts)

　　fｄ=68Hz

　　frequency response

　　Caluculated value




　　1.9cm 90Hz
　　3.3cm 77Hz
　　4.7cm 69Hz
　　6.1cm 63Hz

Evaluation

　　This is the first time to listen to 16cm system. 10cm,20cm FE series
has a heavy duty sound, but this has a gentle sound.

　　Transparency is much better than that of ones with press frame.

　　Ｉt has a fine high tone, but high end is not enough. So we can't use
this system as a profossional sound monitor. It's for consumer use and
for high quality source.

　　In conclusion, is it both sophisticated and sensual?

　　The answer is yes.

After 1 month

　　When volume level is high, bass-reflex works well. But the sound is not
so clear.

　　AST amplifiers don't work well, non-AST amplifiers give good result.
It's a mystery.


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