you cant run too hot or you'll cause the surface of the cloth to become shiny, which is basically just on the edge of melting the upper threads of (presumably ) the polyester in the grill cloth. Since the Weldwood was a contact cement, as I recall I used the lowest heat setting to set the adhesive. Use a silk or rayon setting.
Watch carefully that you dont burnish the surface. Do not use any water or steam, just a dry iron. The hotter you adjust it the better the grab will be, but watch for burnishing.Just take out the iron and play around to find your lowest setting where no burnishing occurs. I seem to recall using an old tee-shirt between my iron and the grillcloth to prevent any chance of burnishing. This technique also allows you to use a higher temp iron w/o issue.
And take some scraps and practice your technique, especially on corners; until you understand exactly how to finish a corner. Trust me it'll be the best 20 to 30 minutes you ever spend, since you dont want to have to pull off a speaker grill cloth and start over because you screwed up the corners....
After I got my technique down PAT I applied Zilch's cloth to four sets of L100T's flawlessly.