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Hi,
A client has a Bösendörfer grand with some central notes that sound metalic; I haven't still senn the piano but he explains me that a technician told him that the reason is some problem with the agrafs. Some of you had experience with it?
Thanks a lot
Mila

The larger Bosendorfers use an agraffe that has a round steel insert that has an edge exposed by the string holes which forms one of the two termination points for the vibrating strings. All the smaller Bose grands I have seen use the standard brass agraffe. These Bose's don't have the "wiry", "metallic" sound that comes with the larger Bose's when you play them forcefully.

Evidence shows me that the "wiry" sound is an artifact of longitudinal mode (L-mode) excitation and reflection. Solid brass agraffes damp more of the L-mode. If I am to rebuild a Bose with the insert agraffes I will replace them with solid brass ones-(unless the client likes that sound). Then you can play the piano as dynamically as your musical sensibilities require.

I agree for the noisy behavior, never thought of longitudinal modes, I though only that the metal is harder or similar hardness than the steel wire, so the wire move on the rod while it vibrate.

Similar problems arise with too hard capo

I have heard that after some time the wire is deformed too much by the harder rod or capo.

The steel rods I have seen are finally used by the steel wire, then , tuning is difficult. I have seen such steel rods under the capo of some old pianos, with similar imprints and noises

Ed, you seem to have some ideas on the vibrating modes, can you tell me how the "quadratic effect" is perceived, and is it noticeable only above a certain force ?

(the tone generated by the back and forth motion of the bridge)

I have a baby grand that has a capo bar even in the bass section. Some notes sound metallic when hit forcefully. A little similar to loose copper, but twisting more does not help. Could that be the same cause?

All imprints can make noises, in agrafes as in capo. The capo need to be rounded for that reason and also because the strings may break if stuck too much in a capo mark.

But the noise can have another cause, could be that the strings are too different in lenght for instance ... (?)

Bosendorfer stopped using the steel reinforced agraffes a number of years ago, at least 10, but there are alot out there with this feature. You can see the pin if you look at the side of the agraffe.

For what it's worth, in my experience almost all tone problems are solved by seating the strings on the bridge and careful voicing, including really careful fitting of the hammer to the strings. That's not to say it might be something else, but I've worked on a lot of Bose's and you'd be amazed at the wide variety of tonal complaints that are solved that way.

Capo bars are a common source but the OP referred to the central part of the piano.

Olek: I am not familiar with the term "Quadratic Effect" being used to describe what modal generation occurs from what I call "Rocking" motion of the bridge. Who and where has the term been used?

I have done extensive work defining what forward string termination conditions work best and I agree that hard capo's or round rod string termination surfaces create noise and string longevity issues.

In the late 1970's I defined and described what the most robust capo bar configuration is: V-bar shaped to a V not a U,
V-bar grey iron not to be case-hardened.

I took some flak from some technicians-but the first piano that I reshaped the capo bar to bring it to a definite V profile over 30 years ago is still in vigorous use and has never buzzed nor broke a string. I still service the piano. I have V-shaped capos on well over 500 grand pianos and none of them has ever had a problem since with noise or wide-spread string breakage.

I haven't heard much protest from my fellow techs in recent years and I know some who have adopted the technique and are satisfied with it. Now if we could get the manufacturers to pay more attention!

Thank you Ed, I am trying today to understand the hardening or not hardening if the iron.
I suggest that the string is well when it creates it place in the iron, but on a very small deep.

Irn specialist told me that the iron used for plates is homogenous, so, unless some hardening have beenn done at the factory, shaping the capo would not lend to a more fragile metal, while I heard that theory more than once (an external layer being harder than the inside)

I am unsure of what you mean with V shape, in my view most capo have that V shape, simply the top of the V is a small 2-3 mm max rounded surface - SOme pianos have a larger one and inverted U shape, but they are not the most common ones.

I am investigating on eventual hardening, knowing it can be detrimental to tone, I just wonder if a light hardening is possible, I was said that heating old semi phosphorous iron can lend to deformation s I certainly will not try that on a real plate.

If you mean shaping the capo in V with a sharp edge, can you tell me how deep the strings make imprints then ?

ABout quadratic effect, I first have seen the term in the Pianotec software, Philippe Guillaume , the designer and developper, explained me it was a pure frequency related to the speaking lenght, and created by the rocking motion of the bridge. making a 4th partial pitch above a certain level of power. A non linear effect

I may admit I hardly perceive it in real pianos, but I perceive a tone change occuring around the action saturation level, that allow to shape a different tone, I always wondered if this was related.

http://www.forum-pianoteq.com/viewtopic.php?id=2269

Thanks Olek;
Case Hardening has been done by some manufacturers (Steinway among them but not always in their history) to the V-bar surface after it has been shaped. Usually the hardening is only at the very surface but sometimes it goes all the way into the V-bar rib.

You can tell the hardness by the sound the file makes when it cuts the V-bar. Some V-bars are so hard the file is ruined trying to remove the round profile and the sound is like two files rubbing together. (Funny aside; Stravinsky described the tone of the harpsichord as two skeletons making love on a tin roof) (second aside; he probably only heard the Pleyels with the iron plate construction).

I shape the V-bar profile to a definite V and the string contact width is held to 0.5mm or even knife edge if the elevations are wrong between capo and agraffe sections. The string self-machines a groove about 1/3 the string diameter and work-hardens the surface enough with tuning to resist any further incursion. The string will NOT cut into the V-bar like piano wire on cheese!

I will look into Guillaume's work, I wonder if the quadratic effect is what Harold Conklin refers to as "Phantom Partials" in the Journal of the Acoustical Society of America.

Good news if the (old I suppose) iron plates can accept such treatment. Do you have any pics of jobs done that way some time ago ?

Do you know how the hardening was made ? I was on the idea to use heat and a powder as the one used for the steel tools to make a hardened blade, for instance, but metallurgy is complicated !

I have been said that up to some era the iron was semi phosphorous because the material was sourced locally.

Today the consistency of the product is way better, and the quality of the grey iron is certainly way more controlled.
This is the actual iron :


(I heard that the "Bessmer process" is used to create the FGL used for the plates (for tone reasons, was said)




http://80.248.221.152/fontesdart.org/ftp/www/index.php?option=com_content&view=article&id=494:cadres-de-piano-la-fonte-et-la-puissance&catid=52:des-ailes&Itemid=54

http://en.wikipedia.org/wiki/Hematite

Short answer to your question is; YES.

Short answer to "Uprights" question that is yes

Hi,
somebody knows what diameter had the Bosendorfer's 275 agraffs from 1995 ?

Thanks

Standard M 6,5 x 75 in my opinion if that is the question. I have some of those reinforced agrafes there, probably.