Hello first thing that comes to mind is that moisture thickened the backrail cloth, at the same time key dip lowers and the hammer raise. 4-5 mm seem a lot but who knows. RXD said the most important thing you may verify. Also visually the way the shanks are at rest can be more or less evaluated.

The worst situation would be a warpage or the keybed with moisture. I have seen that and not under terrible conditions and not on a medium priced grand. The quality or the keybed was in cause and itoor courser bcoffet. s very difficult to correct.. (once moisture was back for accepteable conditions with DC and undercover, situation was a little better but the whole keyframe had to be adapted, with scraping the keybed as well then compete keyboard regulation ) that grand is not far from a large river.
Moisture is high all year long in the 55 60% range usually and more in spring and in a good house well isolated.

Best wishes.

Factory data may help of course but there is so much to look at.

Are you absolutely sure that this isn't a measurement mistake?

One way to roughly double check, is to measure the difference in height between the bass and treble strings, and compare that to the difference in height of the bass hammers and the treble ones. From your description, I would expect the bass hammer line and the treble hammer line to be pretty much the same, is that the case?

There's just a bit of an alarm bell going off here that the picture isn't quite accurate. Describe exactly what you've measured, and where. Which notes, where on the hammers, where on the strings etc. Is the hammer travel distance uniform throughout the bass, and also throughout the treble?

The bass strings are higher on the horizontal plane compared to the treble strings. But, yes, the bass hammers are more or less in line with the treble strings.

Yes, the travel distance is uniform among the bass strings at 45 mm, and also among the tenor and treble at 40 mm.

I measured the distance from the underside of the string directly above the hammer, to the strike point of the hammer directly below. Is that correct?

Yes. And, if you do all other steps (key height, dip, let-off, drop, etc.), you can adjust after-touch last via the method I described before (using a correctly sized front rail punching, 300g weight, and adjusting the capstans). If everything is done correctly, this will give you proper hammer blow distance.

Thanks.

So if my measurements are correct, my question remains to be answered.

Would a pro technician set blow distance differently for the bass compared to the rest, or is this an unacceptable practice for you pros?

Again, may I emphasize that I have no complaints with the piano and it is still blowing me away and I have a difficult time leaving for work. And I have no intention of changing anything again because I so love the way it feels. Especially that the repetition is so improved after the springs were adjusted.

I agree and that is exactly why I'm asking this question.

Again, I didn't say this. What I said was that the action seemed heavier and the *aftertouch* was messed up.

At the first shop I worked at, we routinely set preliminary blow to 44mm in the treble and 47mm in the bass, so yes.

Finally!

May I know the reason for this?

Am so interested in the answer but I may not be able to check the forum for a while. I'm on internet access in my office which has electricity but will be driving home shortly where we do not have power due to the typhoon.

I can see no reason or benefit for the bass to have a different blow distance. You will not find this in any specs for any manufacturer - In fact it would go against the specs for every piano in production.

That being said, you will find professional techs who have all sorts of strange ideas about regulating pianos. The PTG makes some effort to promote standards, but there is no real reinforcement of such.

I've never given it much thought, and never bothered to ask, but I suppose the answer is due to the fact that we increased let-off to 3mm for the bass hammers, which is a safety factor for the bass strings. Increasing let-off distance also increases after-touch, which can be compensated for by increasing blow distance, which decreases after-touch.

Got it! Thanks!

If they did that it was to have more powerful and heavier basses, so the pianos can be sell easier but the let off difference is not a good justification, to me.

Letoff is measured and regulated without the piano actually playing ; when you play the letoff distance varies. Hammer travel is sometime reduced to help the touch when the tech don't know/cannot regulate properly and the action is heavy, or misconceived..

But if the hammers are intended for that and bored shorter in basses then the travel can be larger in basses.

Some Erard grands of the 1900 era had more hammer travel distance in basses , a large 55 and even 60 mm with the rest 50 mm, to have more power.

Rest position is better similar all along the piano in my opinion indeed after-touch can be larger in the basses somehow. When playing it will be similar to higher due to more shank flex. more often I will have more key dip in the basses than having a longer travel distance there.

Dble

Not 40 mm travel but if the pianist is happy with the touch why bother.

The problems may arise after having played enough an action out of regulation With jack buried in cushion this happen, but if not the piano is only not ideally regulated ; if the specs are 45 mm for 10 mm dip it turns out to be 40 and 9 mm also (+-)

Question answered before it was asked. Feel beats regulation by numbers!