Exhibition questions

[Inigo]

When I've assembled my only exhibition soundbox, I'm afraid I'm not using the right gasket size (bore). With the tubing pieces I have, if I install two gaskets of the small bore, they seem to be too narrow, and the diaphragm rests floating with the backplate completely settled down. Too thin gaskets. With two gaskets of The greater bore tubing I have seen to be too thick, for I can hardly keep the second gasket in place. It protrudes from the ring and gets popping out all the time. Then I've managed to install one of each size and they seem to fit, but when installing the backplate, it squeezes the gaskets a bit.
On the other hand, the original gaskets seemed to be of the thick type, and they must have been pretty squeezed inside the soundbox when new. The ossified shape they have is clearly squeezed. Must it be this way? With other soundboxes (no 4) I obtain the best results when the gasket is but slightly pressed, just as needed for airtightness and no more. But the rests of the old gaskets in the exhibition tell another pressure story...
What's the right size? Who sells it properly? I've bought gasket tubing from eBay unknown dealers, and they sell you what they want: a pretty thick tubing with thick walls, not very soft. Do you know a tubing source for the exhibition?

[JerryVan]

The gaskets are supposed to be a bit squeezed in place. Yes, it can be tricky to keep that second gasket in place till the back plate is installed. I use the ⅛" diameter hose, if I'm not mistaken.

I usually make the first gasket a bit too long, which forces the ends together tightly for a nice seam and also serves to swell or stiffen the hose a bit by its being slightly compressed.

[Inigo]

Thanks, Jerry. I'm using the same size as you. It's thick, but very soft, so it seems to be the one to use. So two gaskets of this size will have to be squeezed inside. It's true that when you are installing the backplate, it's a bit difficult, and seems that the are too thick gaskets. But the second gasket eventually pops into the curved border of the back plate, that leaves kind of a groove between itself and the front ring, so the pressure is not as high. I've noticed when pressing the back plate into place, that a bit of twisting it favours this popping into place of the back gasket, leading it to that outer groove.
This must be the original specification of the exhibition: somewhat squeezed soft rubber gaskets, and carefully adjusted hard springs at the needlebar fulcrum. So the soundbox is tuned to this lower compliance at the diaphragm border (squeezed) and also low compliance at the fulcrum. This design is valid provided these two compliances and relative masses are tuned within them. It's not strange, since you can notice another factor: the high mass this small heavy backplate. This provides the needed inertia to convey the vibration energy into the diaphragm. It's known that after assembling, these soundboxes can be tuned tinkering with the spring screws, until an optimal sound is achieved, and this sound must be clear and crisp.
Will try this original adjustment as soon as I receive the new rubber isolator I'm waiting for...
Thanks again!