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Gratings.
I am new to this forum and I wonder if someone might help.
I have this young chang baby grand 5` 2" model g157 year 1988. The soundboard its got crown but I have no way to measure the downbearing at pitch since the strings were all rusty and snapped on me. I checked with the string attached and noticed that the first few strings of the bass bridge ,from right to left, had 0 downbearing and increased gradually till the last string.
That is peculiar to me.
This piano needs to be ready in 2 weeks for a recital and I dont know how to calculate the downbearing measures for the entire piano.

I would really appreciate any help from the experts who share the same passion and dedication for perfection.

This piano uses a cantilevered bass bridge. It is very common for pianos with this type of construction to have no measurable string bearing at the low bass and very little across the rest of the bass bridge.

With this design -- and regardless of brand or piano length -- if you try to load on more string bearing the bass bridge assembly will simply rotate under the added downforce and most of it will disappear over a fairly short period of time.

ddf

If I understand well, part of the idea is to provide a supple bridge, anyway, more supple than without cantilever.

Is the design efficient? Probably in some cases, as it is used by very good brands with some success.

Originally the idea is to allow enough panel back length for the bass strings, as too short they would be "too efficient" , as if too much downbearing was present, which is not good nor necessary with basses.

A good well curved bass bridge seem to be good in any instance, anyway. (the design of the plate must also have some curve in basses then)

We do not need to compress the soundboard, In the basses, so if a cantilever is springy enough to provide some good energy transfer, it may do the job.

Measuring string bearing does not say much about downbearing, in the end.

I see that as a good sign, and a way to evaluate bridge tilt or geometry.

A good distance bearing before mounting strings is good enough, in my opinion (computed)

what would be an ideal bridge to hitch pin deflection for all the section of the piano (without strings)?

from 1 mm to 2.5-mm on the higher point of the board, going down to 1.5 or 1 mm in high treble..'small piano)
1.5 mm in high treble make a bigger angle than 2.5 mm in mediums, due to the short string lenght.

or compute angles; if you obtain 0.5° to 1.5° in mediums once the strings are tense you have a good angle (front). (the digital protractors are good to measure that)

Thanks a lot everybody

Olek thanks for the measures, do they apply for 5`2" baby grand?
Are that numbers with the piano at pitch or without strings?
If they are at pitch what are the measures without strings and how I predict how low the soundboard is going to sink to apply that numbers?

Hope make sense

Sounds like someone has a bit of work to do on a "so-so" piano. How unfulfilling a recital would be on a 5'2" Hopefully nothing more serious than Scarlatti or Mozart.

those are "measures" without strings. on larger pianos up to 4 mm at the highest spot.

But this depend also of the type of soundboard, its condition, , how much is possible.

a too much constrained panel may sound less good if it was not intended to.

not enough force make the tone less thick, on pianos asking for more down-bearing than usual, as Boesendorfer.

the highest point in the board is near the plate break, in the soprano region, or may be a little lower (?) if the soundboard is cylindrical.

For a recital, you may wish to rent a decent recital piano, if possible. Time is too short to finish to a decent quality level job, also taking in account that this seem to be your first restringing job.

The last thing a piano needs is a supple or springy (to use your words) bridge. This lack of rigidity means that the bridge will transfer less energy to the soundboard. Search for some of Del's posts on this topic--he has written far more knowledgeably about it than can I.

that is all a matter of proportions . the needs are differnt in basses and treble

For a piano of this type and size this is probably as good an answer as you're going to get without knowing a whole lot more about the piano.

There is no absolute answer for this question. The soundboard still has crown but is this because there is still some compression in the soundboard panel? Or because the ribs were crowned? In this case it may not matter all that much but it would be nice to know.

Why has the issue even come up? Is it because there was no crown at all before tension was dropped and the strings were removed? Were the mounting devices -- whatever they might be -- changed for some reason? In other words, why has changing the height of the string frame become a question? Why is the string frame not simply put back in the same location and at the same height as it was before all this work started?

In a short piano I'd say there was more danger in overloading the soundboard than there is in loading it too lightly.

ddf

Olek, for the recital this is a second piano of a steinway D.
I dont know if they are going to play together or not but that what they want.

there is still crown in it and I want to make sure that strings deflection is right in case the soundboard dropped for any reason.

Ill put some more info:

piano from 1988 soundboard still with crown

-soundboard 8mm thick in the middle 9 in the treble and tappered to 7 more or less.

-douplex scale front and back

-1 meter front to back 1 meter 45 cm across

-it has 10 ribs 2.2 x 2.2 cm

-total string tension 2361 Lb

-average string tension 157 Lb

-average break point 41%

about that

According to writers at the time the idea was to accommodate the longest possible speaking length in the low bass section at the expense of everything else. There was no understanding at all of the need for a backscale length that was long enough to all at least some, albeit minimal, bridge mobility. They did understand that putting the bridge nearly on top of the inner rim probably wasn't a good idea so somebody invented the cantilever with (again according to writers of the time) the goal of attaching the bridge assembly to the soundboard panel further out in a “more flexible” portion of the soundboard.

Despite the fact that bridge cantilevers were never a good idea they have been used for at least one and a half centuries; it is not just the good ideas that survive through the years. Bridge cantilevers are very inefficient energy transfer mechanisms. They are particularly inefficient at transferring low frequency energy which is unfortunate since that is what they are supposed to do.

And can anybody explain just why bass bridges are curved the way most of them are? Instead of having just a few strings with a short backscale these pianos end up with a whole lot of strings with very short backscales. It is no wonder that so many short pianos have such poor sounding low bass sections. Including many from some very prestigious piano manufacturers. Unless the bridge (and the surrounding soundboard area is able to physically move at low frequencies the piano cannot create any sound energy at those low frequencies. So what we hear is all much higher partial stuff. Typically made louder through the use of massive and dense hammers.

Someday a light may dawn and some of these piano makers may figure out that loud, obnoxious sounding bass sections is not as good as a slightly less loud but pleasant sounding bass section with real pitch clarity and decent timbrel dynamics.

ddf

for instance that one have no problem on basses :



That bridge have little chances to tilt, as can be understood.
despite a small gluing surface it will accept the tension of the wire.

The taller model have a small cantilever on the last basses, just for length progression choice probably.

purely TF65/2 set of rules I guess (if that mean something).


What I read is that on small models, the bridge mass may be kept low and the bridge may be flexible, to avoid raising the resonant frequencies of the panel at that location, that would put emphasis on the large inharmonicity of small bass strings.

The poor energy transfer is not possible to avoid, so the idea seem to be to aim for a transparent bass tone, not as powerful as possible but with a good luminous tone.


best regards

It's hard to tell from the photograph but it doesn't look like that bass bridge has a cantilever. If it does it is very short. The bridge is also placed well out--away from the soundboard liner--into the board and the bass string backscale lengths are relatively long.

This is hardly an example of the typical bass bridge cantilever.

ddf

Yes, I was not expecting you to see a cantilever there, on the taller model 120 there is a small one on the first bass notes.

The size proposed for a light cantilever bridge is with a 3 cm apron, not much if compared with the large ones that where sometime used...

Regards.

Is this statement generally correct? I'm not sure how to take "It is very common." Maybe this refers to 5 ft 2 in pianos with very large cantilever overhangs.

As has been written in this forum before, there are > 6 ft. grand pianos, including modern Grotrian of this approximate length with this bass bridge design.

My old piano has clear, measurable string down bearing on the cantilever bass bridge, as determined by rocking a card with notches cut out for the bridge pins.

Thus I wonder.

Best regards-

When measuring crown and bearing you must also measure the relative humidity. With higher humidity the bearing and crown increase. So comparing crown and bearing measurements must be adjusted for the humidity differences.

Most cantilever bridges have much less bearing at the bottom note than they do at the top of the bridge.

My experience does not indicate that cantilevers are always worse than non-cantilever bridges. I have converted a couple of cantilever bass bridge designs to non-cantilever designs-and I do not care to repeat the experiment.