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In the Forum: Audio Discussions
In the Thread: Magico Mini or Jonathan Valin maxi?

Post Subject: Re: hardfoam conesPosted by KeaAudio on: 7/4/2010

Hi there el Ol

you are on the right track. (I know your post is quite old now, but I just found it today when I googled my own site).
I am the one who invented the Polyepicell cones of Kea Audio.
I bought the patent papers that Mr Podzus made over 60 years ago from the patent office in Munich and studied it (yes it is in German, I am afraid).
In the patent Mr Podzus explains the principles behind his invention to start with. This is: a very light foam structure that has open cells and is very hard at the same time. In his days plastics were limited so he used urea resin (contains formaldehyde). The main idea is that the cells in the foam are rather small and are not completely sealed, therefore the soundwaves can travel inside the material and get dampened on the way to the rim. The amount of connection between the wholes determines the dampening factor, which should be rather high. In order to achieve the stiffness and hardness (high shore hardness, or low young's modulus) he used aluminium (or other metal) powder. The problem with manufacturing was the getting those cells/holes right. He found a way to produce it which is rather tedious at best: first he produced very small wax spheres which were mixed into the resin. Then the whole thing was spread on a sheet of special paper, then formed to a cone and then baked in a vacuum oven, which extracts the wax at high temperatures and leaves holes behind. The surface is rather rough due to the semi open cells so he glued some aluminium foil on top of it. This again is rather difficult and that is why it looks so crappy. (I still have some of those drivers at home, which I measured thoroughly).
Nowadays this can be manufactured much simpler (but it is still not simple actually) with a 2 component hard foam, which is baked as well but not in a vacuum. The formulation of the components allows the material to foam up when mixed and hardens in the baking form. It is essential hereby to have the exactly correct mixture and the correct amount of metal powder added. It took me many years to get to a stage where these cones perform as intended.

But after many trials and errors and long laboring and measuring I achieved an outstanding cone, that is very light and at the same time very stiff, with a well defined dampening factor (very important to avoid ringing). The dampening factor determines the upper cutoff frequency by the way, which I usually set to about 3-4kHz, with a 18dB decay. This makes a crossover circuit for the midrange unnecessary.
If you have the chance to be either in NZ or Germany, you could arrange an appointment to listen. Every customer sofar has been completely overwhelmed by the clarity of the treble, the crispness and punchiness of the bass (which goes very very low by the way!)

Let me know if you have any further questions.

kind regards
Kea Audio
J.Lang

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