![]() ![]() This for sure not a very scientific approach, but it works and the measured values correspond quite well to the resonance of the finished panel. What I did in the beginning was to lay down the one side of the panel that holds the mylar on a workbench and to measure the bending of the film by applying a constant weight (200g) in the very center of the film. If you still would like to measure the tension, there are some different methods, most of them are not suitable for the hobbyist. This also allows to match panels, if desired. By this they are able to decide weather the panels resonance is within the accepted tolerances. They apply this method prior to coating, assembly etc. ![]() Then they look for the maximum voltage at the microphone by running through the lower frequencies of the audio spectrum to find the resonance of the pre-finished panel. To be clear at this point the panel is not connected, it is the B139 that is working. Again above the panel sits a microphone that measures the sound pressure coming through the panel. ![]() What they still do today, is to position the panel under test horizontal above a bass speaker ( in that case they use KEF B139). So if you intend to refurbish Quad panels or build new ones with the same dimensions this should put you very close to Quads specifications.Ĭoming to your question, Quad uses an indirect method to achieve, respectively to monitor the desired resonance. This is only valid if the tensioned area is in the vicinity of some 40 by 80 cm. If you apply these values you will be very close to the original way Quad is tensioning their panels. So, each weight is about 1,5kg for the mid/high and 2kg for the bass. I have seen the original jig, which is now in Germany, and if I recollect correctly they have 30 weights. The original Quad stretching jig uses steel weights which total to 45kg for the mid/high-panel and some 60 kg for the bass-panels. What counts is the resonance frequency, that surely depends on several factors such as material and material thickness, mass, dimensions and the foil tension after the foil is glued to its frame and the weights are released. The tension itself is not a value of interest. Your question is certainly interesting to everyone who refurbishes or builds electrostatic panels. ![]()
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