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Del:
Thank you for commenting on my questions concerning your comments on the 5'8 Kimball grands and how they compared to my 6'7, which is apparently from about 1979 or 1980. You had mentioned in the previous thread https://www.pianoworld.com/forum/ubb...%20made%20to%20look%20g.html#Post1954997 how the backscale length on the 5'8's was too short and that you had made recommendations to Kimball on how that problem could be addressed. I simply wondered if the 6'7 suffered from this same design flaw that they had on the 5'8?
Here are the pictures of the plate, backscale, and bass bridge on mine. Are they close enough and clear enough to show the detail you wish to see?

I actually don't know for certain whether the strings are still the originals, but when I get a moment over the weekend, I pull out my micrometer and measure the diameter of the first and last wrapped bass strings to add those details. I did replace a missing bass string when I got the piano so I happen to have the exact measurements on that one---
It was Key#25, A3, the second last before the break, and it was the shorter of the two strings for that particular note. It's the third string in from the tape measure in the pictures.
Total Length 53.5 inches
Speaking length: 44 inches
Hitch pin to bridge pin: 6.125 inches
Diameter .040 inches. with winding .072 inches.

Thank you for your comments, Del.

It’s close enough to see that your piano does suffer the chronic “Kimball ultra-short backscale condition.”

Look at the ridge that goes along the edge of the frame (plate) casting about ⅓ to ½ of the way between the hitch pins and the bridge pins. On the note your tape measure is resting on the working backscale length actually appears to be approximately 2 ½”.

That’s not too bad—it’s not great, but it’s not too bad—at the high end of the bass section but it’s quite restrictive at the low end.

Were this my piano I’d be grinding off that lip along the edge of the casting and then I’d be loosening those strings, pulling the hitches—or shearing them off and redrilling depending on just how the originals were installed—and installing vertical hitches. This alone would extend the backscale lengths by ½ to ⅓. Assuming they are still working well you could save some money by reusing the original strings.

ddf

Take two thin washers, probably brass, the size of a hitch pin punching. The inside diameter should be almost snug to the hitch pin. Cut one washer in half, bevel the straight edge on the top, and solder it to the whole one. You may need to adjust the thicknesses of the washers. The whole washer can be very thin. The half washer should be thicker. You also may need to ream or file the hole for a good fit. Replace the punching with this, with the half washer to the back side to hold the loop up above the whole washer. This will replicate the geometry of a vertical hitch pin.

You could probably have a machine shop make a whole slew of washers like that for less than your time is worth, and put them on any piano you want. In any case, it is probably easier and cheaper than changing hitch pins. It is reversible, too, in case you do not like it.

This can work and I've done it on occasion but the hitches can also bend. I've had that happen as well. Having done both I prefer vertical hitches. Still, as you say, washers are easier, cheaper and faster. If it works. Still have to grind off that lip.

ddf

Thanks, Del. And BD.
I see what you are saying. I went out to the web to find some pictures of the backscale lengths for some other pianos, and I found this one. Wow, that is quite a distance, yes.




So, that ridge on mine is certainly in the path of the string--and touching the string, obviously---and is unnecessary. I wonder why they even put it there in the first place. How odd.
I'm thinking of trying to file 2 grooves for the strings for a couple notes (which may be the only option I have for the time being considering the piano is sitting in my living room and not in my workshop) and comparing the difference. I imagine grinding off the entire ridge is not going to be an easy job, necessarily, or very neat for that matter, but I'll certainly put it on my job list.

I cannot say I understand what the significance of a vertical hitch pin is, though. So you are saying that a vertical versus angled hitch pin also affects the sound? That is amazing; how did that ever occur to someone that that would be an issue?

Thanks to both of you, again, for your comments and suggestions.

The ridge on your piano is there to set the bearing in the bass. It is used throughout many pianos. Without the ridge the bearing would be set by the height of the hitch pins. Its easy enough to raise the hitch pin height by using different thicknesses of punchings. If you have to lower the height, you can only lower the plate which also lowers the end of the treble bridge. A ridge lets you grind off height any where along the bridge without changing other bearing settings.
Vertical hitch pins allow you to set bearing anywhere on the pin (within reason). The plate has to be set to allow a range of movement.

Vertical hitch pins can improve the bass response by allowing the string termination to pivot on the pin instead of being bound against the top of the plate. That's the theory anyhow.

Why would you bother messing with a backscale that already has a cloth weaved in there to mute it? Do you honestly think you will hear a difference? Take a guess at how many tuners out there actually bother to tune in a duplex scale? You will be surprised at the answer.

If you raise the strings above the ridge with shims you will likely see a more noticable depreciation in tone from the reduced downbearing than an increase in some appreciatable mythical harmonics you have no idea what they will be. Besides, the manufacturer put those hitch pins in with no consideration one would bypass the ridge. Nothing an extra weave of cloth won't take care of but is this all worth while? People buy a Baldwin for a Baldwin sound and they buy a Steinway for its sound and so on...seems like a big waste of time and effort to me unless someone wants to illustrate constructively what is to be gained?

I don’t know why Kimball did this. Several other manufacturers have done it as well. A recent Blüthner concert grand comes to mind. There are others. It seems to have been a more common design “feature” among European pianos than U.S. pianos.

Interestingly this does not seem to limit the “power” in the bass section but it certainly does affect the “quality” of the sound.




The vertical hitch pins—take a look at Baldwin grands built from the 1970s on—simply provide a way to free up the entire backscale. There is no bearing bar so the backscale length is measured from the back bridge pin to the center of the hitch pin.

Were I doing this job in the home I’d certainly consider BDB’s suggestion of simply placing one or more washers over the existing hitch pins. Whether or not you can use this method depends on two interrelated factors;
— The height of the bearing bar.
— The amount string bearing required.
Usually the frame (plate) height is set for correct string bearing at the bearing bar. When the bearing bar is removed string bearing is set by the height of the strings on the hitch pins. With vertical hitch pins you simply move the strings up to the appropriate position for the amount of string bearing you want. This may be too high for the original—softer—pins with washers being used to set string bearing. The metal used is of necessity soft so they can be bent after installation. If the strings have to ride too high on these pins they simply bend under the tension of the strings.

ddf

These are two different issues. Stringing braid has nothing to do with the clamping effect of a very short backscale. Nor does this have anything to do with "tuning" a so-called "duplex" scale. (Or, more accurately, an "aliquot" scale.)

Yes, I honestly think there is a positive difference in the tone quality of the bass section when making the design modification I have described. I think this because I have demonstrated and proven it many times in my own rebuilding work, my design work and during my seminars on strings and stringing scales.




That is why I described removing the ridge (or bearing bar). Done properly string bearing ends up right where it should be. The theory behind this modification has been covered several times on both Piano Forum and on this list. As noted above, it is also discussed in my seminars.

What is gained is more energy in the fundamental and lower partials of the bass notes. This gives the notes better articulation and better pitch clarity. The improvements are real; there is nothing mythical about them.

ddf

Del, I was simply wondering about a couple things on this procedure. First, what is actually happening, physics wise, that would allow a lengthened backstring that is dampened out with a weave (and partially with that back bridge pin)to increase the fundamental and lower partials on the speaking length? Since the speaking length is not modified can I assume there is a more efficient transfer of energy to the soundboard for some reason? Also, is the cloth weave removed after this modification?

I usually keep an extremely open mind when things are modified in a way that there is an addition of something to a manufacturers design. The skepticism comes in when someone undoes something (removes the ridge) which the manufacturer went out of their way in design,time, and expense to do.

I have had one of these Kimballs in my shop some years ago.

I agree, not the most desirable design. The Kimball in the photo's can be rebuilt with it's current design. Properly executed, it can be a very rich sounding piano.

Emmery I'm not Del, but I will try to answer your question.

If the back-scale is too short it restricts the movement of the bridge. Bass strings are already heavy gauge plus they are doubled up by the helix. A longer back-scale allows the string to have more flexibility which allows the bridge to move more freely.
Vertical hitch pins not only give longer back-scales, but also allow the hitch pin loop to move freely adding more flexibility.

Whether the back-scale is tuned or not has no bearing on the system.

The stringing braid has nothing to do with the mobility of the bridge. For the purposes of this discussion we can ignore it. It may or may not be used after the modification is made; it is a whole other issue.

Picture the system in cross-section. The strings pass over the bridge (through the bridge pins), back to the bearing bar (in this case the cast riser on the hitch pin panel), then down to the hitch pins. The backscale is measured from the trailing bridge pin to the bearing bar.

Now, picture what happens when the speaking string is struck by the hammer. The hammer strike sets up an oscillation wave motion in the string. This wave motion travels back along the string until it reaches the bridge. In response to the vibrating energy in the strings the bridge physically moves. How far it moves depends on a number of factors among which are the stiffness of the soundboard panel and ribs, the mass of the assembly (including the some part of the soundboard, the ribs in the general vicinity and the bridge[s]) and the clamping effect of the backscale.

To under this last, go back and study that cross-section view of the system. Imagine what would happen if we moved the bearing bar right up next to the bridge. Keep in mind that we don’t have just one string passing over the bridge and crossing over the bearing bar; we have many of them. Also keep in mind that these wires are under fairly high tension and they are made of fairly stiff wire. It shouldn’t be too hard to visualize how the combination of very short and very stiff highly-tensioned wires will effectively clamp the bridge in place; it will prevent the bridge from moving in response to the vibrating energy in the speaking length of the string. It doesn’t matter what is going on in the speaking portion of the string the stiffness of this very short backscale is preventing the bridge’s motion. I call this the clamping effect of the backscale. Leaf springs in automobile suspension systems are long for a reason.

To get a better picture of this take a piece of the thickest music wire you have in your shop and clamp it in a vice with only, say, a half-inch protruding. Flick the end of the wire and see what happens. Depending on the diameter of the wire it won’t be much. Now adjust the wire so there is a full inch protruding and flick it again. You’ll see more motion and it will be at a lower frequency. Now give it two inches; you’ll get more motion and it will be at a still lower frequency. Now give it four inches….

Now picture what happens when the bearing bar is moved further away from the bridge. Make the backscale, say two inches long. The clamping effect of the backscale is reduced and the bridge can move further in response to the vibrating energy in the strings. In other words, the bridge (and the soundboard assembly to which it is attached) has greater freedom of motion.

You also have to understand that it takes very little soundboard motion to create relatively loud sounds at high frequencies. It requires much more soundboard motion to create meaningful sound power at very low frequencies. And the fundamental frequencies of the lowest notes of the piano are, indeed, very low. In audio reproduction circles this is sub-woofer territory. If you’ve ever examined a sub-woofer you’ll have noticed that speaker baffle (cone) is held in place with a very compliant surround—it has to be very free to move in response to very low frequency energy inputs.

The modification I’ve described approximately doubles the effective backscale length in this piano. This gives the bridge and the soundboard assembly to which it is attached greater freedom of motion; the backscale is not clamping the bridge down as tightly and restricting its motion at the very low fundamental frequencies present in the vibrating strings.

None of this alters the energy spectrum in the vibrating speaking portion of the string; it affects only the clamping effect of the short backscale against the bridge. There is already some energy at the fundamental and lower partials present in the vibrating string; this change merely allows the bridge (and soundboard) to move more freely in response to that energy. All other factors being equal a bass section with a short backscale—high clamping effect—will produce little or no sound energy at the fundamental pitch of the vibrating string while a bass section with a long backscale—low clamping effect—will produce at least some sound energy at the fundamental and lowest harmonics.

ddf

Del, does the modification affect the overall efficiency of energy transfer from the string to the soundboard and/or sustain? In other words are there any good or bad side effects?

None that I am aware of. The energy in the vibrating strings at the fundamental and lowest partials is wasted if the bridge/soundboard assembly is not able to move. I’ve never made this modification to this model Kimball grand but I have made it to numerous other pianos with a similar problem. Granted that other changes and modifications are being made at the same time but overall sustain is, if anything, improved.

As well, when I set up side-by-side comparisons on my string test device the side with the longer backscale produces sound energy at the fundamental and the lowest two harmonics—the other does not—along with longer sustain.

ddf

I have a Steinway Centennial in my shop right now.

Anyone familiar with these pianos knows they have monstrous back scales. Everywhere.

Someone had previously rebuilt this piano with a new sound board and pin block, very pretty gloss finish on the plate.

From all outward appearances, a job well done.

The piano was totally anemic.

We have the board out and after taking all the measurements, whomever rebuilt this piano knew nothing about the art.

So, here we are with all the great back scale we could ever want and the piano was lifeless.

My point is, with out the art, you don't have much. With the art, the Kimball with it's short back scale can be very good.

BTW, the Centennial is #38351.

And my point is that the Kimball with a longer backscale in the bass section can be much better.

Steve's piano does not need complete rebuilding. This modification can be done while retaining the original strings. Certainly, there will be some time and effort involved but the result is a cleaner, more articulate-sounding bass. If this is important to the pianist then this is one way to get it without completely rebuilding the instrument or replacing it.

ddf

I thought that the main problem was originally that the bridge finish really near the belly. then possibly having a longer back-scale would free a little the soundboard but I would need to hear the result.

When I see bridges that near the belly, they are generally cantilevered.

Raising the wire on usual plate pins, I would be afraid of the pin bending, particularly in the basses where the tension is high.

Art is certainly necessary, but art uses mathematics and physics laws, not only some "feeling" (while "art" may get better in time after experiences, very certainly.

I like the non glued round part of the soundboard, on the Foerster grand, gives a very open while powerful basses.

The restriction to soundboard freeness is certainly what is killing the tone quality of many pianos.

Thanks Del,

I am not trying to challenge your comments. I apologize if it comes across as that.

I think there is something important to add. Perhaps I need to rephrase my comments.

Calling all Scalers:

I've been redesigning scales in my rebuilds for decades but I am still at a loss to determine the bottom line truth concerning back scale. I've gone around and around with Ari Isaac about the issue and see his points and value his advice but I just can't make it equate in what I have left of a mind.

As they say of older folks, one of the benefits is that we are down to a managable number of brain cells. I plead guilty.

I'm in the process of designing a pair of pianos for my own use. While I do not thing it makes a lot of sense to build over the top instruments for the public market, if a guy who knows how to build pianos, has what he needs to make them and is willing to do the work wants to make his own "dream" piano, then more power to him.

I am such a man and have no illusions of marketing. Just want to make sure I've covered every base and embraced every concept before getting started.

Would anyone be "in the know" concerning how to determine a good length for a back scale. I have every option open to me from inches to feet and no set opinions...yet.

Just looking for anyone willing to offer an opinion.

DR