I've noticed that in some pianos that I play, the transition from the agraffes to the capo bar is quite rough. I'm not sure exactly what the term is called, but since It seems like kind of "break" ( like the bass-tenor break), I thought that I'd refer to this by the above term. if there is a proper technical term for this, please do correct me.

The main question I'm expressing is: has anyone had the experience that a treble transition from agraffes to capo bar is rough, and has a change in tonal colour (from more smooth and rich to more lively, and brighter) that annoys them or otherwise affects their playing? I'm interested to know.

As per my post on the current 'duplex' topic, yes there is often an obvious tone change at that area usually around note 54/55 where the capo bar starts but only when played loud. Normally it's only the first two or three notes where the zing is most obvious and generally only when played really hard. Play the first note of your duplex section hard and hear the bright lively zing, then put a small piece of cloth on your finger and mute off the three strings of that note in the area between the front duplex and the capo bar. Play the note hard and it will sound almost dead in comparison. Some customers accept the zing for what it is, some find it so irritating that the tech has to mute the offending strings at the front duplex, or mute say two of the three strings to create a smooth transition from one section to the next. Sometimes judicious toning is all that is needed. The treatment varies depending on the customer and the make/model of the piano.

On some pianos, although the strings in the mid section have no capo bar/front duplex, the tiny length of string between the stringing felt and the agraffe may have a perceptible zing when played hard, you can use the above test to see if your C7 does it.

My one (C7) doesn't do it, but other, newer ones do it. Duplex is possibly part or the equation, but I am more curious about the influence of the capo bar, not the duplex. But then again, one affects the other, so I guess...

The metal bridge before the capo is scaled. The capo takes the place of the agraffes. On the Yamaha, when played hard, this area produces more haromonics and has more tonal effect than the rear duplex and that is what you are hearing. ie it's just an inverted, more effective, version of the rear duplex.