To my understanding there are two main families of Yamaha hammer actions and every action is a variation on one of them:
- GH - their main action from long ago that has gone through some internal modifications and improvements through the years
- GHS - their entry-level action, it’s light in total weight (doesn’t mean it feels light when played though)
I’m not sure about the exact difference between the two families though. I guess they have slightly different geometry and components which contributes to the GH feeling tighter and more controlled whereas the GHS is slightly looser and clacking.
Some actions have the X in their name which denotes the presence of an escapement simulation.
Some actions have 3 in their name to denote the presence of 3 sensors to allow for repetition without fully releasing the key but there are actions that have three sensors without 3 in the name.
NW denotes having wooden sides which, as discussed, is only a decorative thing.
Some of their actions have something like initial friction, mostly their recent actions but not sure where it comes from and whether there’s something in the name.
In one of their materials Yamaha says the GH3 swings back faster to facilitate faster repetitions.
So, it’s a mess 😀
I think the BHS is just a non-graduated version of GHS with the lightest zone from GHS used throughout the entire keyboard.
NW-GH is some variant of the NWX without the X, i.e. without escapement 😀 I also think from my memory that the NW-GH in the CP88 doesn’t have that initial friction of the NWX in the P515 but might be wrong.
I think I may have to test them both since it’s ultimately down to how they feel with the corresponding sound engine and the key to sound connection. Because we’ve seen how one and same action can feel very different in different pianos.
