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Many factories set blow distance some shallow knowing full well it is going to settle (increase) over time. There may also be some who specify a shorter blow distance for some mechanical or action ratio reason.

An example might be a piano with particularly heavy hammers that has been balanced with a relatively (numerically) low overall action ratio. By setting a slightly short blow distance they could still use a reasonable key stroke (i.e., not too deep) while still providing an adequate amount of key aftertouch.




Generally small variations in hammer stroke—by themselves—do not have a great effect on the acoustical power produced by a piano. Assuming, of course, that the rest of the action parameters are regulated accordingly. If you really are hearing a significant variation in acoustical power—as opposed to a perceived difference—I’d be looking somewhere else to find out why.

Subtlety is achieved by making sure all of the various regulating parameters are precisely and correctly adjusted to balance with the chosen hammer blow distance.

There is nothing magical about this; it’s really just a matter of several different lever ratios working in synergy with each other. Unless you are prepared to modify the overall action ratio—Not advised unless something is screwed up in your action and you really, really know what you are doing!—then the appropriate hammer blow distance ends up being a compromise between the physical location of the hammer relative to the bottom of the pinblock and the rest rail (or cushions) at the back of the wippens and the desired amount of key travel and aftertouch.

In most pianos there is enough room to move the hammers a little closer to, or further away from the strings than is specified by the manufacturer. It is OK to experiment with this as long as you remember to compensate for the changes in hammer blow distance with suitable adjustments in key travel and aftertouch.

I suspect that if you fully re-regulate the action after changing the hammer blow distance you won’t find all that much difference in overall acoustical power. You will notice a change in how the action feels and this is often translated into a perception change in how the piano sounds.




Yes, the string height, as measured from the keybed, can vary considerably from section-to-section as well as within a section. This is a function of how “flat” the casting patterns and molds are, how the string frame twists and warps as it cools and how it is machined and drilled. In theory modern string frames should be somewhat “flatter” than their predecessors because the machinery doing the cutting and drilling is now often NC (numerical) or CNC (computer/numerical) controlled. Many string frames are now cast with a little extra iron in critical areas and the milling/drilling machine simply hog their way through cutting off the excess and leaving the V-bars and agrafe drilling seats relatively flat. But, obviously, this is not always the case.

In terms of a piano’s performance a string frame would have to be wildly out of square before there would be any noticeable degradation of tone.

ddf

I'm surprised by Mark being the only one to mention key dip in relation to blow distance. Whenever I think through action mechanics, I try to keep in mind that the first act of mechanical movement is the arc of the fingers pushing on the key tops. I bring this up because of the relationship of the key dip to both the blow distance and the players hand.

Key travel and key dip are the same thing. I prefer the term key travel as being more descriptive of what is actually happening; i.e., there is a direct relationship between hammer travel and key travel. Key aftertouch is a part of the overall key travel. (But you knew that....)

ddf

Are these statements equivalent in practice?

Interesting question. Let's see if I understand it correctly, I would say yes except that there are usually more constraints on hammer travel than there are on key travel. That is, the maximum height of the hammer at rest is limited by the bottom of the pinblock and its minimum height is limited by the wippen and/or the shank rest rail. (Yes, that is adjustable but only within its own limits.)

So, if one wanted a particularly shallow (i.e., short) key stroke it may not be possible to shorten up the hammer travel enough and there may not be adequate aftertouch. Or, if one wanted a particularly deep (or long) keystroke it may not be possible to increase the hammer travel enough to accommodate.

On the other hand, it is usually possible to set the hammer travel anywhere within the physical limitations of the piano and still come up with a key travel setting that will work; i.e., one that will drive the hammer through its desired stroke and still have adequate travel left over for an appropriate aftertouch.

ddf

There is something relative to hammer blow distance and that is the position of the knuckle and jack at rest, as well as at letoff moment.

SO the hammer blow allows for some variations but the range is not so large. (grand piano)

If the force actiing on the knuckle is pushing on its side too much the knuckle will deform even the wooden core can bend in time , and the knuckle on old pianos is often warped if not unglued, when the hammers have been filed a lot or if the "overblow" is very large (which is not uncommon on some brands)

WHile refining, indeed the stroke can be modified to change the touch or the tone (while it is sometime faster to change directly the key level)

The jack to knuckle relation is changing the dynamics of the shank on one side, and the suppleness of the keys on the other side.
We can use a range from a somewhat "hydrolic" keyboard, to a very springy one, just with variations in jack/knucle and aftertouch..