The nice thing with "Tygan" speaker cloth is it cleans up easily. I have been cleaning the front of the radio. With the speaker removed I brush on foam cleaner, brush it in well then use a vacuum cleaner to suck off the remaining foam. I do this bit by bit so as to not allow what's under the cloth to get too wet.
Here you can see the difference between the top two strips which I have cleaned and the rest.
It helps get rid of that dirty circle which always shows where the speaker aperture is and where the dirt and dust has collected.
Dont try this with conventional cloths though, only with the woven nylon "Tygan" type cloth and certainly not with silk cloth, foam cleaner dissolves the silk.
Mike