Piano World Home Page Forums Our Most Popular Forums Piano Forum Downwieght, upweight, friction, inertia

Although I've in the past read some articles and PW posts about these related topics, I'm still not clear about exactly what each one is and how each relates to the perceived touch on a piano. For example, why is the often mentioned downweight not so critical in how a piano's touch feels?

Are there any good but not too complex articles or videos that deal with this? Of course, feel free to post your own comments about these topics but I know I've really posted multiple questions here so a good reference might be easier.

Hi Pianoloverus- complete amateur here as you know. I always thought my C3 had a medium touch. Light enough for me to do decently fast runs up and down the pianos. Somewhat heavier than my GB1, light touch. Apparently some GB1s typically come with a light touch. When I asked my piano tech to measure the action on my C3 he said the down weight was 52 grams, which supposedly is right in the middle. I’ve always been impressed by the evenness of the action. After he regulated it this past June, I became even more impressed. I noticed when I played the Schimmel C169 last week, the touch seemed a bit heavier but I could quickly adapt if I bought it. When I played the CF4 it had a medium down weight but was buttery smooth so it felt like there was minimal friction. The Bösendorfer 214VC that they let me try was even more silky smooth. The Estonia I bought had a very smooth, even action that was noticeably lighter than the Yamahas or the Schimmel. I feel a bit guilty going back to a lighter smooth action because I’ll be spoiled, but at this point in my life I don’t have to quickly adapt to other pianos for recitals or for playing friends‘ pianos. I know it’s not very helpful, just wanted to give you the amateur view.

Greetings,
These weights, in grams, are the diagnostic data that we use to determine ratios in actions. Ratios of leverage and ratios of weight. Down weight, (DW) is the number of grams needed to cause a key to depress to the point of contact with either the jack tender or the drop pad. A slight bump on the action to overcome static friction is usually used to set the weight. DW in the middle of a grand ranges from a light 44 to a heavy 60. Normal is 48-52.

Up weight is the amount of weight that an action will lift when it is placed on the front of the key.

A key can be weighted to overcome too much SW (SW for "strike weight", which includes hammers and shanks) and leave an action with a very heavy key, normal DW and a low UW, due to all the lead. This action will feel light when played slowly but play like a truck when a pianist. tries to play fast for loud, as the inertia of the heavy key will begin to offer more resistance to acceleration. This is why DW is not the be all and end all of action characteristics. A lighter key will have more DW and UW and will respond more evenly to increased dynamics.

The weight of the hammer is critical, and should be selected for maximum tone. Bigger is not always better. We vary the ratios in the action to accommodate the optimum hammer weight for that piano, but there are limits on how heavy a key can actually be. Normally, a key with a front weight heavier than 30 grams in the middle of the piano will exhibit the inertial problem. A big concert grand action might have a 40 gram key at the bottom of the bass, a smaller piano would more likely be in the 35 gr. range as a max.

The action is limited by the height of the sharps, (1/2") and the need to keep them from "burying" under the surface of the naturals. This requires about .070", so there is only .430" travel available, at most. Original Steinways used a key dip of near .390", but more recent models are using heavier hammers and the ratio was altered many years ago to take care of the wieght by increasing the key dip. Some modern pianos will show near .420" dip as the longer ratio is used to overcome excessive weight without resorting to an overly heavy key.
That is a light sketch, Ed McMorrow can offer more specific parameters, as he has deeper experience in action weight and geometry than most. .
regards,

Hello plover,

I hope you get many helpful responses. I'll chime in. The specs are the best attempt to quantify what feels good to most people. Plenty of people have preferences that are outliers.

The goal is to eliminate excess friction so that fewer weights are added/needed for balance.

The goal of the placement of those weights is to reduce inertia, because high inertia specifically contributes to fatigue.

The goal of down weight and up weight is to be within ranges, but the more important measurement for good "feel" is typically the spread between the down weight and up weight.

If a suitable spread cannot be achieved, then changes to the action geometry are in order. This could require different parts, moving the action stack, moving an action rail, moving the capstan. The one critical pivot that is often wrong but cannot be moved is the key balance rail, but when make a new keyset (Roseland plug ), then we can address that problem, too. When that is the case, the client can specify the parts they want to use, and all of the measurements can be taken backwards to place the balance rail in the right spot.

So rather than trying to nail the down weight and up weight separately, if a compromise must be made, then a more optimal approach is to control the spread. This is why the down weight isn't as critical to the feel for most pianists. If the down weight is high, but the up weight is also high with a reasonable spread, then it is an easy adjustment for the pianist.

Reducing friction is an ongoing process over time, and it throws off the other measurements as it comes back into the system. Additionally, friction doesn't come back evenly across the piano. Over here, it could be key bushings, over here, it could be action centers, and at the same time, the brass capstan is slowly tarnishing and adding to the overall friction...lots of things for a technician to chase down, measure, and treat. A piano sitting and not being played will still be affected by friction changes that require service to remedy.

Piano Loverus,
Thanks for your questions. I will only focus on one so as to be as brief as possible and that is the question of why downweight and upweight measurements tell you nothing about touch quality.

The way we measure touch by seeing how many grams of weight will start a key moving and how many grams a depressed key will return are best describes as "static" measurements. The key is moving much slower than when we play music.

The effects of inertia are more readily felt when one attempts to accelerate the hammer more rapidly. This is because the action has leverage on the hammer. The hammer moves about five times as far as the key and all action parts move in a portion of a circle. Inertia rises with increased acceleration and physicist describe this type as rotational inertia.

Since the piano hammer moves more distance than all the other action components the mass of the hammer determines the majority of the resistance to a change in velocity an action exhibits.

The industry has a habit of attempting to reduce a heavy feeling action by adding front weight, (key leads), to the keys to "help" the pianist start the action moving. Once the pianist starts moving the keys faster than the force of gravity wants to move the leads down, the keys actually begins to resist your efforts significantly.

The upshot is you can have an action that measures "light" for static downweight but feels heavy when played fast and/or forcefully.

I have shown by example many hundreds of times that one can have an action with static downweights of 65-70 grams, that feels light to a pianist. It is all about the hammer weight.

Hofmann wrote about the force differential between soft and loud playing that a pianist should feel. He wanted actions to play softly with enough resistance to support the hand and arm. This resistance reduce the muscle effort needed to hold the arm/hands above the keys while playing softly. He said too much muscle tension is introduced when a pianist has to hold their hands up with too much force. In other words, the playing is not relaxed enough and this causes damage to the muscles/nerves. (I am paraphrasing Hofmann here. The writing I have is very terse).

And when the keys are moved forcefully the action should disappear into your body. (These are my own words).

The wonderful thing about low inertia high leverage actions is they are very stable in regulation, can easily tolerate changing friction, wear very slowly, and don't get crazy bright with use.

Very interesting! Someone like Tobias Matthay would disagree with Hofmann on "hovering" at the undepressed level of the keys, then applying just enough force for pianissimo playing, as being good technique. But when I start spouting Matthay, people either don't understand what the heck I'm talking about, or they completely disagree with it and give me a bobcat fight over it. So, I'll shut up.

Sounds like the industry wants to make piano actions too firm, techs work hard to to make them medium, pianists disagree about what medium feels like, and it all boils down to heavy hammers.

Of course, you could just take all that massive felt off the hammers, and just use the thinnest wood for hammers, and have minimal mass, and the hammers would leave the strings extremely fast. But the piano would not sound very good.

Theories about mass and inertia are not the only thing that matter in piano design, and any theory that does not take into account for those other things is useless.

Bearing in mind the disagreements as to what is light or medium or heavy, I would guess that in addition to all the physical attributes and constraints of the pianos, you have those of the pianists, their fingers, hands, arms, etc. A whole host of individual factors.

Colin Miles, I find there is far less disagreement about what feels good in touch resistance.

But there is great disagreement about how to determine this.

Technicians who measure my actions will conclude they are monstrously heavy. Pianists who play them find them light. Who you gonna trust?

BDB, well you have done a very poor job of explaining what work you have done on hammer weight. And you sure haven't shown up at my shop to experience it for yourself.

BDB wants us to think him an expert on touchweight, but he has never shown that he does the "heavy lifting" of this work.

I have never claimed to be an expert on touchweight.

Those who do claim to be expert seem to want to make people jump through hoops rather than answer simple questions.

I had an amazing experience with the feel of an excellent playing action.
When I was beginning to become aware of the complexities involved in action geometry and touchweight. I went to many technicians shops and stores, and I would play on their pianos. I would find a few here and there that I thought were fantastic at the time. But then, I went to Darrel Fandrichs shop in Stanwood Wa at a PTG Chapter meeting being held there. And I sat down to play on one of his pianos. The action was so silky smooth that you just kinda melted into it. And your fingers and hand would not feel any fatigue whatsoever. Immediately the other fantastic ones were no longer so fantastic. Darrell and John Rhodes Invented a system called "Weightbench" that weighs the key weights , evaluates the action ratio for optimum inertia. In fact, up until their research, how to measure inertia in an action, wasn't too well understood. I highly recommend reading their published articles in the PTG Journals.
-chris

I have never seen BDB claim to be an expert in this area. I think you are off base on this assertion.

PW's own Roy 123 has published some superb material regarding inertia and touch. It is some of the best information available I have read on the subject.

Hi Ed - Would you have titles, links or ISBN numbers to Roy 123’s published info? It might well be too technical for me but I’ve always have been fascinated with the piano as the intricate, delicate, complicated machine that it is. Thank you so very much.

j&j, I think you could PM ROY123 here on PW. It would take me some time to find the material.

j&j,

This is the link he put up on the forum some time back.

Inertia in a Grand Piano Action

Thank you Sam! Time to dig out the “readers” 😁.

These topics make worthed visiting the forum, thank you to the contributors McMorrow, Foote, Chernobieff.
There is an unrelated item to this topic, but it does affect the pianist's perception of the touch-weight, I am referring to the characteristics of the tone, the best way to illustrate this effect is by experiment with a digital piano. The touch-changes on a digital piano are purely done by changing the (touch curve) making the piano deliver different tonal quality and volume to a certain amount of pressure. These changes in tone and volume affect the perception of (some players) creating a lighter or heavier feel, this effect occurs with acoustic pianos as well.