The production of thin molded parts of Al²O³ hard ceramics (Alumina) for use as a sound-producing loudspeaker cone.
The starting point for the cone production is a thin aluminum foil, which is completely oxidized in a proprietary process and converted into alpha-corundum by a special burning process. For this purpose, the aluminum foil is thermoformed into the desired shape and placed in an anodising bath after special heat treatment. This procedure makes the light silvery pure aluminum convert completely into brittle, largely amorphous aluminum oxide of dark gray color. In a three-stage combustion process with temperatures of up to 1,450 ° C, the Al²O³ molecules are rearranged in an alpha-corundum lattice. This process causes a 7% volume increase and successive pore channel formation in the nanometer range. The end product is a snow-white and extremely hard cone which can be cut into shape with a CO² laser. From this point on, mechanical processing is no longer possible.
In order to understand the advantage of this complex production, the general requirements for a loudspeaker cone can be briefly summarized as follows. It should be 1. light, 2. stiff and 3. with high internal damping. Since these requirements are mutually contradictory, conventional cone materials are strongly compromised and can be regarded as unsatisfactory in one or even two of the above-mentioned requirements.
Our special material makes it possible to realize all requirements without compromise. The suitable selection and processing of the aluminum foil allows very thin (< 50µ) and thus the production of very light molding parts. Due to the extreme hardness of the material (Mohs' hardness 9), we get inherently very stable cones which in their mass/stiffness ratio are only surpassed by cones made of beryllium (highly toxic - and not used by Accuton) and CVD diamond (tweeters and mid-range drivers are available in high accuton® quality).
The comparatively high internal damping of our ceramic cone is guaranteed by the special production process. As the oxidation progresses towards the center of the material from both sides, an interface is formed in the middle of the membrane. This ultimately consists of two mutually interlinked partial membranes, which damp each other. The pore formation mentioned above also leads to the development of further interfaces transversely in relation.
This foam-like microstructure has a significantly better internal damping than, for example, a sintered ceramic part. Not to mention the countless counterfeits, which are declared as ceramic speakers and have merely a more or less ceramic coated surface and essentially retain the properties of the base material.
Compared to conventional materials, our loudspeakers with our ceramic membrane have a better impulse response and significantly reduced distortion ratios (THD - total harmonic distortion and IMD intermodulation distortion) as well as an increased bandwidth of linearly transmitted frequencies. As we produce tweeters, midrage and bass speakers with similar ceramic membranes, all the required drivers of a loudspeaker-box can be equipped with the same membrane material, which also ensures the homogeneity and neutrality of the sound.
This has been recognized by major manufacturers in the high-end sector and in the studio industry, therefore our accuton® ceramic drivers are now available in many loudspeakers with reference status.