Pioneer's edgeless fullrange

Introduction

Why I build closed enclosures properly is because I didn't know how to
calculate parameters of bass reflex system.

2 Differences between air cannon and bass reflex



Open a small hole to a paper box, it is an air cannon. When you tap
one side of box, mass of air flies out of the hole. The shape of the air
is like a donut. You'll find it on slow video. On the other hand bass reflex
system has a duct with length. Therefore the air in the duct is pushed
and later pulled by the air suspension in the box. These mass and
suspension colaborates into duct resonnance
.
And if ever duct is too short, bass reflex will be an air cannon.

3 Long duct vs. short duct

The method to calculate fd of Helmholtz resonatoris as follows.



For example when we build on enclosure which fd is 100Hz,



We can make one with such a long duct,



or with such a short duct. Which is better?

4 Enclosure with a short duct

I'll build enclosures with small duct because I have ones with long duct
already.






( In the case of FE103 diameter is 93mm, and pioneer 8cm diameter is 72mm)

5 8cm edgeless unit

This time 8cm edgeless unit is employed which is use in pioneer's S-ST7.



This unit is inner attachment type, so precise round hole is needed. For this
purpose trimmer is very good. When I cut wood smokes, for the trimmer
produces much heat.

Port was cut with drill. To perform that was rather difficult. Pine wood was
employed to build. It looks beautiful.

6 Impedance (bare unit)



　　fo=220Hz
　

Duct length 4.5cm

Impedance


It looks queer. The sound is out of balance.

Duct length 6cm

Impedance


Frequency response


Fd is rather high, but the sound is good.

Duct length 7.5cm

Impedance


Bass guitar sound is away. Notes are only trace. To hear these notes effort
is compelled. I think there are many products like this which is tuned out
of music notes. If we bought these products, tone controls or other devices works
in vain.

After all duct length became 6cm. This time no paint was emploed.

(August 20, 2000)

Appendix（Acoustic tuning method)

I invented new method to tune duct. Holding a speaker with one hand taps cone
lightly by a finger.Taping sound is taken by microphones into computer and
observed its spectrum.


Rch



Peak is read as 150.7Hz

Lch



Peak is read as 150Hz



foc is read as 226Hz

Bass reflex has a merit to boost bass reproduction by staggered way.
Especially when we reproduce electric bass guitar sound, setting fo as 220Hz
and fd as 150Hz is very effective as well as when reproducing double bass.

Drived with AST amplifier

Ordinay low output impedance amplifier is not enough for this speaker
system. YAMAHA's AST amplifier with current positive feedback will
work well.




above: Kaneta's method flat amplifier
below: YAMAHA YST-M15

index