Dear @terry9 : Thank you. Unfortunatelly the fixed ones hasvery low pf capacitance and are NOS so we can't get it in future and along that in reality for different reasons needs a special circuit board to use it. It's not a true viable " excellent " option for a phonolinepreamp and non-imaginableforcrossover speakers.
In the other side I read somethings about that kind of capacitors:
" One disadvantage of using air as a dielectric in a capacitor is that it has a relatively low dielectric constant compared to other materials. This means that a larger distance between the plates is needed to achieve the same capacitance as a capacitor with a higher dielectric constant material. Additionally, air is not suitable for use in capacitors that require a high level of stability or precision."
that could means bigger dimensions that other caps.
" In summary, an air capacitor would not be a viable energy storage option because the flowing air would not retain a dielectric constant necessary for the capacitor to work properly. "
"
An air capac is a capacitor that uses air as a dielectric, and this capacitor can be designed in fixed or variable capacitance form. The fixed capacitance type is not often used because there are different types of fixed capacitors with much better characteristics than it, so the variable capacitance form is more frequently used due to its simple construction.
Air capacitors are usually made of two sets of semicircular metal plates, which are separated by an air dielectric material. Of these metal plates, one set is permanent and the other is attached to a shaft that allows the operator to rotate the assembly to change the capacitance when needed. When the overlap between the two metal plates is large, the capacitance is higher. Thus, the highest capacitance condition is reached when the overlap between the two sets of metal plates is maximum, while the lowest capacitance condition is reached once there is no overlap. For better capacitance control, finer adjustment, and higher accuracy, a reduction gear mechanism is used.
In addition, the capacitance value of air capacitors is very small, ranging from 100pF-1nF, while the operating voltage range is from 10 to 1000V. The breakdown voltage of the dielectric is small, so the electrical breakdown inside the capacitor can change, resulting in poor operation of the air capacitor. "
So, for me at the endyour adviselooks as useless in practic audio way.
Btw, the self by-passing Multicaps means higher developed inductance that's not good and maybe from therecomes its kind of coloration that's away from the neutral Wima/Vishay or Kemet ones. Only my opinion through first hand experiences.
Thank's again, I learned.
R.