When I play B4 I get a huge resonance on F#6 which is the first undamped note. ( There is a tiny resonance on G6 when C5 is played but not at all annoying, and no other annoying excitation of undamped strings above G6. ) It makes B4 stick out as if it was improperly voiced, but if I dampen F#6 when playing B4, B4 sounds the same as the surrounding notes. Any ideas to reduce the energy transfer?

Do not know that piano but check backscales in low mediums and basses, where the lenght allow to have such notes sounding.
Sometime very active. In need of more tight ribbon.

Thanks Isaac. I have checked and they are quiet.

It's a feature! 'Enjoy!

Thanks a lot! I was hoping for a "how to install your own extra damper on a new grand" tutorial.

Soundboard resonance? If so could it's frequency be changed with weights or riblets? What do M&H say?

I am confused. If I very gently dampen F#6, using a felt mute laid horizonally on the three strings, the sound of B4 matches the sound of the surrounding notes. If I undampen F6, or E6 and play A#4 or A4, I get the same sound as B4. It seems to me that M&H could have added another damper to the rail. There is room.