Got a call this morning from a small holiness church concerning broken treble strings on a Kawai baby grand. He thought it was around a 1998 0r 99 model, I haven't seen it. Apparently this has been a chronic problem and currently has 7 or 8 broken. I gathered from the conversation that the player is quite heavy handed. I've seen this before. I don't at all feel qualified to do any touch up filing on the plate especially when it is over such a large area. Another tuner has been maintaining the piano, so I can't say if the replacement string guage is correct. My question: If i find that the replacement string guages are correct, would smaller strings help? say down a half a guage of a full guage? Like 14 1/2 to 14, or 13 1/2 ? The dealer who sold the piano blames it all on the pianist, but they had no problem with their old Baldwin acrosonic that she beat the snot out of. This is a small country church about two hours or so from the dealer.
Steve

You might consider checking with a Kawai service rep before you do anything.

Some years ago I had a similar situation with string breakage involving a gospel-style situation and a Yamaha vertical. I talked with a rep from Yamaha, and it turned out this had happened with a number of pianos of this model/period. The problem involved bass strings, and the company was offering a standard choice to customers: a cash settlement or a set of lower-tension bass strings. Yamaha's handling of the situation was exemplary.

It seems like a Kawai rep might offer some helpful bit of advice to you, at least regarding your idea about altering string gauges. I'd want some "official" approval of an idea like that before I tried it, in case someone questions it later.

Jeff

Despite the Acrosonic, the dealer is correct. Most likely the Acrosonic just couldn't deliver the power enough to do it.

I've dealt with a number of churches with full-tilt Rock-like Gospel music with this issue, and many brands of pianos in them, all with the same kinds of problems.

The first thing to do is file and reshape the hammers back to a proper shape. They are probably very bad right now due to all the pounding. This will most likely reduce the incidence of broken strings significantly. Due to the continued pounding, they must be refiled periodically, and the hammers will need replacement after a couple filings.

If it remains a problem, you can limit how hard she can pound the strings by reducing the key dip a couple mm, raising the hammer line several mm, then correcting the other regulation pojnts as needed to compensate.

I am familiar with what Mr Smith mentions, but those were bass strings, not treble. Most of these heavy-hands situations involve broken bass strings. In fact I have changed out bass strings for a low tension set on a number of grands. It's not just uprights that suffer, and I really wouldn't call it a fault of the maker. However, in those pianos we still had to file hammers and sometimes queer the regulation as mentioned above. The low-tension strings helped somewhat, but on their own do not eliminate the problem.

Also, I don't know how often this piano receives hard playing or for what duration, but I've seen a number of heavily used, hard-played grands that needed an entire restringing within 10 years due to string fatigue- which not only makes the strings break easily, but also the tone gets bad and kind of 'clangy'.

One problem you may have if you are out in the sticks so to speak, is finding a technician with the adequate knowledge and technique to deal with these issues. It's likely you may encounter a lot of avoidance unless you can locate the right tech for the job.

Another thing that can help a lot is to make sure the pianist has a lot of monitor volume in her face. Make it so if she plays too hard she gets an earful of herself and maybe she will back off some on the pounding.

Changing the gauge changes the tension to the same amount, so the string's ability to resist breakage remains the same.

I'll second the suggestion to amplify the piano and make sure to point a speaker right in the player's direction.... up on a stand next to their ear is a good choice! Many times it becomes a losing battle trying to be heard over electronic instruments and drums.

Then again there are just some players that are able to pop strings - the Kawai may just be more efficient at transferring the impact from fingers to strings than the Acrosonic was! Check the hammer shaping as suggested and let them know that even with changes, a lot of damage has been done, leading to possible future breakage... (time to re-string the whole section?)

Here's the formula for tension I have:

T = 0.0023 * (fLd)^2

Where f is the frequency in Hertz,
L is the vibrating length (agraffe to bridge) of the string, in inches, and
d is the diameter of the string, also in inches.

So tension should be proportional to the square of the gauge, no?

--Cy--

Ditto to all of the above, especially the monitor. My guess is that there is none presently and this could make a substantial difference in how hard the pianist pounds, maybe (some people just play that way). In spite of its lower inharmonicity, the Kawai has fairly high tension in the treble. Changing the string gauge would definitely lower the tension but also upset the scaling. It is a trade off (just as it is with wound strings), so before doing this, please do check with the manufacturer.

Also, altering regulation to get less power is an uneasy compromise. The pianist might just pound harder and not like the "feel". Strings break because of metal fatigue, period. Filing hammers may help a little but will not undo any metal fatigue already present. Starting with new strings (perhaps at an altered gauge) and new hammers will give the piano a fresh start but the new hammers will have to be maintained (frequent filing) to slow down the inevitable progression back to the breaking strings syndrome.

Also on the subject of wound strings breaking: I've seen in a few cases where many wound strings were breaking that the reason is because of poor alignment. One of the strings was being struck more forcefully than the other. This caused the pianist to pound harder and break the strings which simply got over used in comparison to the ones which were barely struck at all.

I suggest new strings in that section in addition install a new set of hammers. The old hammers will be too hard, and in my experience, filing them helps, but the strings soon start breaking again -so filing is a temporary solution. The breakage is due to metal fatigue. Clean up the bearing points before installing the new strings.

As Cy's formula clearly shows, the tension goes down by using a smaller gauge. However, the thinner gauge wire is less able to withstand a given tension, so the break point % remains almost the same when you decrease or increase the gauge. Therefore, from a string breakage point of view (BP%), you gain nothing by changing to a different gauge. Only changing the speaking length will help, which is not so easy.

Of course bass strings are different because you can control the wrap size as well as the core size.

Thank you, Jerry

Thanks for all the helpful replies. I'll see the piano Tuesday. Wedding Saturday hence touchup Friday. Like I said, another tuner has been maintaing the piano, so I may find something funny, but probably not. I'll replace the strings with the correct size for now, that's the safest. Won't have time to shape hammers and regulate for now. Complete hammer replacement and re stringing at least above the top break with an in-your-face monitor is probably the way to go . I'm sure the dampers tend to interupt the fatigue process. Anyways, I'll contact Kawai, but I gotta get them through the rehersal and wedding first. I'll be back.
Steve

That makes sense; thanks, Jerry!

--Cy--

Steven Bolstridge,

If you would like to measure speaking length and wire size, I'll plot the tension, Inharmonicity and BP for you.

I'll post the results here for evryone to see.

THanks Larry. I'll try to post Tuesday night. My curiosity wheels are really turning, as they should. I have been tuning a square grand every year for the past fifteen years. It was rebuilt somewhere in Atlanta and is able to be maintined at A-440. All the string guages are much smaller than the originals so the piano sounds on the twangy side even for a square. I assume they used a smaller guage to maintain a slight down bearing on the horseshoe section of the bridge, which seems to be the weakest area on most of them. So what I am gathering is that, yes, the tention will be less with smaller strings, but for the purpose of this discussion, smaller mass makes for a weaker string and therefore would fatigue as quickly as the correct string while degrading the sound quality. And a larger string would require more tension. I come across pianos with replaced strings that are too large a guage put on by some tooner, and the inharmonicity is overwhelming. I'm not about to question the scaling of a Kawai. I just want to get it right while upgrading my knowlege base.
Steve

Looking at Cy's quoted formula, to change the tension of a string, the only real variable here is the diameter!(You certainly don't want to change the frequency or length) Can you change the diameter of the string? YES!
Using the correct size string, remove 1/2" of the winding from the bottom of the string, which will effectively reduce the diameter(mass) of the string. You can now use less tension to get the same frequency.
note: On some pianos, you will need to match the winding lengths of bichords, but before you do,try it. I have had it to work.
Wayne Gregory-Angier,NC

To follow up on my original post, the piano is a Kawai GM2, 4'10", 2001 with a mostly beige plactic action. Capo bar throughout, two treble breaks and a tenor one. Former broken strings are: G4, A5, C6, D6, F6 (doubles). Strings I replaced today were: G5, G5-G#5, A#5, G6, G7, G#7. I thought by the original call that there were more and just in one section. After confirming the guages of the broken ones, I went with the original as stenciled on the bridge, no reason to change anything. If the problem persists (as I suspect it will) and they okey the work, I'll re string the two treble sections or more, re-surface and voice the hammers, and regulate. This is a very small church with a set of drums, two guitars, bass, keyboard, mandolin, and several tambourines.... I gave a mini lecture on decibel temperance and the art of listening to one another.
Steve

There are at least two variables I worry about when using stenciled gauges (are there more to worry about?):

1) Whether adjacent strings of the same gauge are to the right of the mark, or to the left (i.e. do they start with C8 and go down, or at the bottom end of the bridge and go up?);

2) Whether the gauges are metric or not.

I'm glad you confirmed what was there.

--Cy--

Steven,

I'll get back here tonight and post some info on scales I have done. One right now, the original is horrid, from 1900. Not that you are working with a scale that old, but it does demonstrate the some details discussed here.

Fortunately, there are many scaling programs that make adjusting the variables simple.

Back in 1985, it was a spreadsheet in Lotus 123 and plotting the points by hand on a paper graph....I remember how much work it was.

I also have a book of plain wire statistics. You don't need a computer to plot plain wire sizes. If you want to have info right at hand, you can add this book to your "Pierce Piano Atlis". I'll get the author and publisher and post it here.

The real perspective in scaling comes from applying the designs to the piano. In other words, stringing the scale and listening to it.

Sorry for the delay in getting back here.
Shop is beyond busy....

The Book is:

"PIANO REBUILDER'S HANDBOOK OF TREBLE STRING TENSIONS (AND OTHER CHARACTERISTICS)
By James H. Donelson, (R.T.T.) RTT is on the book's cover.
My copy is copyright 1977

Of course this book can easily be used in the field to determine if there is a tension problem causing failure.

Any chance we can get the speaking lengths in question along with the wire size?

You can tell by whether the top (or bottom) mark is at the top (or bottom) note. If the top note is marked, all lower notes are the same size, until the next mark..

Please excuse a layman’s interjection, but there is something I don’t quite understand.
Assuming that resistance to breakage is directly proportional to the cross sectional area of a string, then reducing string diameter should have a much greater impact on reduction of mass, and hence required tension, than it will on reduced strength. For example, a string 1/2 the diameter will have 1/4 the cross section, but only 1/8 the mass. Shouldn’t that make smaller strings proportionally more resistant to breakage? This is the same high school math that tells us why a mouse has proportionally smaller bones and greater strength than an elephant.

I am sure there is something obvious I am missing here.

The tension for a given pitch is also proportional to the mass. It cancels out.

Frank Hubbard discussed this, and said that there may be some slight advantage to thicker strings due to metallurgical factors akin to case hardening, but those would be smaller in pianos with thicker wire overall.

Larry, The church was filled with home school moms who graciously allowed me to tune while they were in another area. I didn't measure the speaking length, but I will next week when I retune again. Thanks for taking the time. I'm gonna order the book.
Steven

Had a similar experience with a Yamaha CF in a church with guitar, drums, organ (electric) and heavy handed player.
The answer was to continue to replace broken strings while lecturing to the music coordinator that this heavy handed player was abusing the piano.
De-regulating made him play harder. Good regulation with softer hammers reduced the incidence of broken strings somewhat. Miking the piano also helped but the player needed to hear the volume from the speakers. When this player left for another church the problem disappeared.
Piano's are not made to withstand this sort of abuse.
One alternative that I considered was Pure Sound stainless steel wire but it never came to that - thankfully.

Stainless wire has a lower breaking strength than piano wire.

Which was the source of my question. I realize that mass and tension are proportional - but string cross section is not. Mass should vary by the cube of the diameter, but cross section only by the square. This makes me think a low mass, low tension string would would be relatively less likely to break.

The mass is proportional to the area of the string times the length, not just the area of the string. If you vary the diameter, you are not varying the third dimension.

FWIW

SPL = speaking length and is in Millimeters
INH = Inharmonicity

Note 65
gague ... SPL .. lbs ten.. %break .. INH
35 ........ 175 ... 164 .... 53.1 .... 2.28
36 ........ 175 ... 174 .... 53.1 .... 2.41
37 ........ 175 ... 184 .... 53.1 .... 2.55
38 ........ 175 ... 194 .... 53.1 .... 2.69

You can see that the %breaking point remains the same.

Inharmonicity is going up. As the wire becomes larger in diameter, for a given length, it becomes more "bar like".

Tension is, of course, going up.

Here next we vary the speaking length. The wire gague remains the same.

gague ... SPL ..lbs ten ..%break .. INH
35 ....... 175 ... 164 ... 53.1 ..... 2.28
35 ....... 180 ... 174 ... 56.2 ..... 2.04
35 ....... 185 ... 184 ... 59.3 ..... 1.83

Now breaking point is going up.
Tension is going up

Also, inharmonicity is going down.

For a given wire size, as you increase the speaking length, the wire becomes less "bar like" and the inharmonicity goes down.

Great discussion on scales.
I think scutch made one very important point. Deregulating only makes the pianist play harder. Sure the strings aren't getting hit as hard but think of the knuckles.
Breaking strings really has a lot to do with hammer shape. More than just the way the strings are deformed, the compression or spring like action of the hammer is improved by shaping the hammer. Think the small end of an egg. Actually the hammer should end up looking like an egg. If you look at a new hammer, it is pressed with the greatest width at the center of the moulding. You cut this down till center of the widest point is 1/4" of so lower than the center of the moulding. That's where the egg look comes from. This causes you to taper the hammer more gradually or steeper into a tip with the radius the size of your thumb(average). A lot of felt is removed.
The reason this is more effective than needling is you have softened the spring of the hammer without reducing it's resilency. Needling improves bounce at first but will not rebound vigorously if over done. By shaping to reduce to support of the shoulders, the compression of the hammer through it's entire spring range is more even and smooth, imparting a far better wave pattern to the string. Tonal quality and volume is improved for the same blow and the pianist backs off.
Hammer shape is essential to the rebound. Slow rebound mutes the strings. Smaller rounder tip and less shoulder makes better rebound. Take an egg and draw a line halfway from top to bottom. See how most of the mass sits below center?