Audiophile magazine gave blueprints of three different enclosures called Onken. Two of them was designed by Koizumi the founder of Onken.
The first one was written in 1977 by Jean Hiraga. It describes what we can call the original Onken enclosure which uses an Altec 416-8a (see
here).
In this article it is true that Hiraga states that the Onken enclosure is not a bass reflex but a dampened low pass filter.
The second one was also written by Hiraga in 1982 and describes what is called "la petite Onken". This enclosure use an Altec 414. In this article, Hiraga dont speak anymore of dampened low pass filter. There are some formulas given by Koisumi but which differ from those of Small. Some are missing because Koizumi wants to keep them secrets and it is impossible to understand how this enclosure was modeled.
The last one was written in 1982 by Jacques Mahul, who founded the Focal entreprise. This article describes what is called the «mini-oaken» (
link). This enclosure uses the 10C01 Focal loudspeaker.
In this article Jacques Mahul has study the «petite Onken» and found that it can be considered as a vented-box following Snyder alignement with Vb/Vas.Qts^2 = 6.34. The mini-onken was designed the same way.
One must be remembered that the original Onken enclosure was designed by Koizumi in 1965. It was before the work of Thielle and Small on vented-enclosures which take place in the early 1970. It was therefore not surprising that the modeling differs.
The claim "the chosen solution here accepts a much smaller speaker volume" comes from another enclosure designed by Jean-Hiraga this time which uses an Altec 604E.
The text :
"The chosen solution here accepts a load of much smaller speaker volume (around 190 liters, instead of the usual 350 liters required for a 15 in. woofer) without experiencing a sharp decrease in sensitivity over the low frequencies, none of the usual sound colorations when a large woofer is associated with a load of small volume. This goal has been reached successfully thanks to the merging of several means : no back-chamber/throat (decompression) but a tuned load (BR) thanks to a laminar vent situated under the speaker itself, to adequate filters and, finally, proper internal padding on wooden walls made of an optimized sandwich of plies.*"
is the translation of the french text which advertises this enclosure :
"La solution choisie ici adopte des charges de volume beaucoup plus réduit, proche de 190 litres seulement, sans que ces systèmes souffrent pour autant ni d’une baisse importante de sensibilité dans le registre de grave, ni de colorations diverses se produisant lorsqu’un haut-parleur de gros diamètre est associé* une charge de petit volume. Cet objectif a pu être atteint grace à la synergie de
divers moyens : charge décompressé, mais accordée, grâce à un évent laminaire périphérique inférieur, à des filtres et traitements mécanico-acoustiques internes et à des parois de structure sandwich optimisées. Ces solutions combinées permettent d'atteindre l'objectif recherché, le haut rendement avec toutes ses qualités et sans ses inconvénients."
This is more like commercial arguments than technical ones. This does not really describe how this enclosure is designed. It seems that this enclosure use resistive-vent.
