What makes an acoustic piano touch 'heavy'?

Question

Acoustic pianos (grands and uprights) exist in a huge range of key weights, going from very light to very heavy. I was wondering what exactly in the piano makes the difference? Is this the same for a grand as for an upright?

Is it, in general, possible to change this and make a light touch heavier or vice versa?

Answer 1

In broad terms, there are three elements that determine the feel of a piano.¹

1. The amount of energy required to get the key moving;
2. The amount of energy required to keep the key moving;
3. The sound of the piano.

Overall "types" of feel

Some piano actions (keys) feel stiff when you begin to press them, but then loosen up. Pianos like that remind me of crème brûlée: hard top, but soft underneath. Leaving aside dysfunction (like rubbing against other keys), an action where the balance of actual weight is more toward the hammer end than the key end can give this effect. It's take a little more to get the hammer moving, but then it has enough inertia to keep moving with relatively less energy from the pianist.

Some pianos require a more constant weight on the keys from the pianist. In this case, the balance between the key end of the hammer end of the action is likely more equal.

Adjusting the feel

In both cases, the absolute weight of the action is somewhat less important than the balance. One way that balance is maintained or adjusted is by the placement or removal of weights at the key end of the piano. The image below shows the weights placed in a Baldwin grand.

In the case of the particular instrument shown above, the action was also made lighter in absolute terms by reshaping the individual hammers to be lighter.

Psychoacoustic effect

Beyond weight and balance, the actual sound of the piano influences its feel. Brighter pianos will tend to feel lighter, while darker pianos will tend to feel heavier, even the if the actual weight/balance is identical.²

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Notes

¹ _{I discuss "feel" here, rather than "key weight", to avoid the literal weight of the key and other elements of the piano action, and instead focus on the perception of weight.}

² _{My primary source is a conversation with piano maker Darrell Fandrich, which I have confirmed in my own experience with pianos.}

Answer 2

There are many moving parts in a piano action and depending on so many factors, they all influence the "weight" of the key. Key depth, single or double escapement action, the wippen, the repetition mechanism, how tight all these parts are such as the keybushings, friction, and there are even external factors which can affect it such as temperature and humidity. Also, some pianos such as the Steinway are prone to vertigris.

Ultimately, if ANY piano feels stiff to you, you are most likely playing improperly. First, it is the weight of the arm that depresses a key. If you try to play from the long flexor muscles, you will experience fatigue, cramps or sloppy technique. There are other muscles such as the pronator, supinator, and even the bicep plays a role. There are no muscles in the fingers so finger exercises and "building strength" is a myth. Technique is all in your head.

Remember being a teenager and going through a growth spurt and you tripped over the floor or fell walking ups stairs? That is because your brain needed time to figure out the new measurements of the body. Once your brain figured it out, you were able to walk again. Once the brain figures out the length of the fingers, the weight of the arm and other ancillary movements, they keys are effortless to depress. A single bad habit can stall technical growth.

What hampers pianists mostly is not necessarily not using the proper muscles but using the improper ones. Abducting, twisting the wrist, playing with a still or quiet hand, not playing in/out, not playing on the edge of the keys, not playing with circular or shaping motions, pressing into the keybed, not playing to the point of sound, playing from the fingers, etcetera.

If you would like to play something heavy, find an old Tracker Organ in a church and play that. Old trackers have mechanical actions where when you press a key you are actually moving a four foot piece of wood. Every pianist and organist should play one because it immediately exposes your every technical flaw. If you find the keys hard to press or you can't play evenly or you fatigue quickly . . . your teacher failed you. Playing a Tracker