Cleaning Large Advent speaker grill cloth

Having owned Advent's in the 70's with their off white grills, heres a great way to clean them without removing from the grill frames. The brown color in the grills is more than likely from cigarette smoke. Buy a can of Resolve high traffic carpet cleaning foam. Spray the grill until the foam settles than use a soft bristle brush and gently brush in a circular motion
than wipe away the dirt. Repeat if necessary. They will look like new. If you need new Advent badges for the grills you can buy them on eBay. 

I'm a bit late to this party, but I've got some experience with renovating the Large (well - any of the early Kloss designed) Advents. A word of 'note', maybe even 'caution': do try and salvage the original cloth. It is an integral part of the design, if you are going for "what Mr. Kloss intended". Due to the nature of that tweeter - and I'll assume you've got the original 'dual dome' on the masonite board, mounted at a 45 deg angle - he used two layers of cloth,  holes offset slightly, attenuate some frequencies.  There is a later tweeter that is a bit smoother in response, but still uses the dual layer grill (IIRC). This is wildy contradictory of what modern grill's are supposed to do! :) Listen to them, with the cloth off - if you like it, that's great - but I did want to chime in on the attenuation 'thing'. You can 'replicate' the cloth and the attenuation by using one layer of generic black speaker cloth, and the outer layer of tan 'vintage cloth' like what is used on guitar cabs. Hold it up to the light and play around with it's orientation. Have fun! b.

+1 czarivey

might be the best way to go, unless you are trying to somehow preserve exact originality.

you can find plenty of grill clothes clean and brand nu at partsexpress.com

Just a thought here but I honestly don't know the outcome?
What if you took the speaker cloth on the frame to a drycleaners and asked them for a professional oppinion?

When I get to such a speaker, I remove the cloth from the frame, via staples or the glue they are held by and wash it in warm water and dish soap. Lots of dish soap. Then go on to more aggressive cleaning solutions, if necessary.

Reglue is by a warm iron, and the thickest pant hemming glue rolls one can find at the local fabric shop. This is exactly what the original manufacturers use.

Start in the middle of each length and work toward the corners. That's how you stretch a painter's canvas for stapling and the same way you stretch and mount a grille cloth. Move evenly out from the center, on both sides of the given center of each side. Always doing each side evenly with respect to one another (all four simultaneously).

Watch web videos for paint canvas stretching, to see how it is done.