What is your membrane diafragm?
Any idea why the Amazing Kapton/alu Carver used sound so good?
The diaphragm is 6-micron (0.00025" thick) Mylar C, with 10.5" x 46.5" radiating area and weighing just under a gram (absent the coating). The Licron Crystal conductive coating adds about 1.5 -2.0 microns and a bit more weight-- still lightening fast.
My friend Ed rebuilds those Carver ribbons at a reasonable price. Unfortunately, Ed says the original 1 mil Kapton material is no longer available but he found a company willing to make up a batch of 2-mil Kapton with bonded aluminum conductors. Ed made up a little hand powered rotary thingy that corrugates the film, like the originals. It's a bit heavier ribbon than the originals but it sounds really good--- extends to about 15kHz, I think.