Ear plugs reduce any noise, it is unbeleiveable to hear someone say ear plugs can reduce the engine noise on other large aircraft like the 747 or 777 but cannot reduce noise created in the passenger cabin on an A380.
The noise level in the 747 crew bunk area must be far noiser than any noise in a passenger cabin on any large aircarft.
I often use ear plugs on short and long flights (as a pax) to cut out the din some of the other pax seated near me make especially with young children.
My ear plugs work very well and reduce all noise levels to a very agreeable level including cabin and engine noise. I cannot hear the flight attendands speaking to me with ear plugs in place.
Perhaps they should try out some different types of ear plugs.