Piano World Home Page Forums Our Most Popular Forums Piano Tuner-Technicians Forum Theory of hammer blow distance...

Seem to be quite a few opinions on the issue. And obviously the impact of the distance between the hammer at rest and the lower face of the strings has a major impact on both the tone and the feel of the piano.

Are there any agreed on rules of thumb for the "ideal" or "preferred" distance for the modern grand? Is 4.5 to 4.7mm or, say, 1 3/4- 1 7/8 a good starting point? Does the bass deserve a little more distance than the treble? Or should everything be kept the same? Does more always translate into louder?

My humble opinion and experience is that it doesn't matter much.
Upright soft pedals move hammers closer to strings with little or no loss in power.
Keydip and let off are much more sensitive.
When looking to rob from elements of the regulation triangle, blow distance is always the first to go because the tone and response doesn't change much for even a decrease of 10mm IMHO and experience.
There are so many more elements that contribute to power. The elasticity of the shank, for example.

I’m not sure there is any particular “theory” about hammer blow distance.

The starting point is usually set by the physical parameters of the piano. In what we call the “modern” piano the distance from the bottom of the pinblock to the string plane it typically around 38 to 40 mm. Sometimes a little less or more. It’s about 6 to 8 mm from the top of the dropscrew down to the hammershank center. Plus there needs to be a little clearance between the bottom of the pinblock and the top of dropscrew. And, usually, we don’t want the hammer to rub against the bottom of the pinblock when the action is removed from, or replaced in, the action cavity.

Add this all up—and assuming you don’t want the hammershank to over-center at hammer impact—and you come up with a hammer blow of somewhere around 45 mm. Some pianos have a hammer blow specification of 48 mm but this is usually because there is more distance between the bottom of the pinblock and the string plane.

ddf

An old Erard grand that I worked on must have had a blow distance of about 60-70 mm. So it has gotten considerably smaller since then.

Yes "theory" is a fancy word for "approaches to".

Anyhow, to put the discussion into some kind of context: I asked Hailun for specs on the 218. The "official" hammer blow distance for the 218 is "4.7mm" but "4.5mm" for a new piano (a little less than 1 3/4") but I quickly realized that these numbers were pretty theoretical.

For one thing, the strings of the middle section of the 218 (a3 to f#4) are NOT level, but actually slant down towards a3 from f#4! So a uniform hammer distance would have required the hammers in this range ALSO to slant down, which they did not. So the hammer drop in effect DECREASED towards the A3, by about 1-2mm (I haven't measured it exactly), by virtue of the fact that the hammers themselves were level. (That setting didn't make a lot of sense to me. One would think that the hammer drop should remain more or less constant in the trichords... Go figure.)

My new piano "out of the box" measured something like 4.4mm for the trichords and 4.6mm for the wound strings. After playing with the let-off, which to my taste, dramatically improved the feel of an already very nice instrument (I decreased it to the min I could get away with without bobbling), I noticed in passing that the hammer drop seemed a little shallow (small) for my taste (4.4mm in the trichord region; 4.6m in the bass).

I tried various different (increased) settings and found that 4.6 was a better sounding ballpark for me on the trichords, especially once I had decreased the let-off: I got a better tone and more dynamic range (without any doubt) in the trichords. The wound strings I set closer to 4.6-4.7mm.

So it seems to me anecdotally, that increasing the hammer distance has a huge impact on both tone and loudness. 4.7 was too loud and not enough control in the treb (trichords) 4.4 on the other hand was not enought "hit" or potential power, for want of a better word, when needed.

But you can't leave the let-off out of the equation.

The tight let-off seems to be important in the overall equation, since once the hammer blow distance is INCREASED (closer to "factory specs"), the let-off makes pp and quick repetition still easy to achieve. If I were merely to increase the blow distance, absent refining the let-off, it seems to me that pp and fast repetition might become much more difficult.

44mm (under 1 3/4") just seems a little too short a distance for hammer blow distance, at least in this case. Can I take that as a safe generalization about hammer blow distance, I wonder? Are there large grands out there that are routinely set at 4.4mm blow distance for the trichords? Are there professional pianists who insist on that kind of setting?

I ask because I'd be willing to experiment with the 4.4mm "limit" in the trichords if I thought it were something techs routinely did. Something tells me that it isn't.

"The starting point is usually set by the physical parameters of the piano." Del

That's the key phrase! In setting up an action for regulation, I look at everything even including how much of the drop screw I want showing above the hammer flange. As I think about it, the amount of blow is about the last thing I pay any attention to except as to how it affects let-off, drop and aftertouch.

I suspect that reliable repetition, even checking, and durability of the regulation are more important than hammer blow esoterica to most of us.

Did you read my threads on the regulation triangle?

You are leaving a lot out of the equation.

For me, aftertouch needs to be appropriate and uniform, for great feel and expression. This is the key to proper regulation, IMHO. Also, keeping aftertouch as an ideal in your mind, allows you to more easily grasp the theory of how all the other elements relate to each other. (Only one other poster in this forum claims aftertouch is unnecessary for proper mechanical execution, but we are talking about feel here. Most technicians I know agree and agonize over aftertouch.)

Jack knuckle alignment must be uniform or all other specs will need to be uneven to some degree to achieve uniform aftertouch.

Keydip will affect all other elements of the triangle.

So, when you are monkeying around with hammer blow, of course you are setting the whole mechanism out of whack and you will get inefficient energy transfer which results in huge variations in tone.

In my course, I am very succinct in how I describe the way the action works and how to decide what to adjust.

In simplistic terms, you must have appropriate aftertouch for any combination of Blow/Dip/Letoff. Changing any one of these will affect aftertouch and requires that you adjust one of the other two to preserve aftertouch, assuming it was good before.

Finally, any technician will tell you that proper regulation and proper relation of the triangle elements has a dramatic affect on tone. After I do a regulation, I am always impressed by how much the tone has improved as well as the uniformness of the response.

I hope you have a better understanding now of the larger picture; if you want to get into the action and start changing settings, you understand now that you are incorrect if you make assumptions about the ideal settings for this or that without understanding how all the elements work together. I say this from experience; I have relearnt much more than I know due to my own incorrect assumptions. This is a humbling skill; individual knowledgeable technicians have a long history of broken assumptions IMHO, I know I do.

As simple as your understanding of regulation was entering into this thread, that is my understanding relative to many other concepts I catch a glimpse of now and then. Like shank stiffness, balance hole friction, downbearing, downweight, upweight, action geometry, etc. Understanding how all these elements and more relate is necessary, the more precise one wishes to regulate.

Good luck with your project. Use and understand the elements I, and others are presenting and you will have much greater success.

Do not dismiss the comments of other experienced technicians. For example, when Del Fandrich refuses to pin down an exact theory on hammer blow, and describes vague limitations like the height of the pinblock and nothing directly related to tone, you should have a pretty good idea that it is not as critical as you think it is, unless of course you don't know who he is.

I hope you do not find any impoliteness in the tone of my email. Truly, I am very excited about the thought of someone with a beginning understanding of regulation, suddenly grasping the weight of certain ideas and experiencing the effect of specific and understood adjustments on an action for themselves. I wish I could be there.

All the best.

Absolutely 100% agree. Too little or too much and/or uneven aftertouch is annoying not only for techs, but also for pianists, even if they don't know it.

I am not sure how anyone can measure tenths of a mm in drop. In any case, these measurements are close to twice what the drop should be in a properly regulated piano.

I suggest you bring in a technician to go over the regulation details.

"Is 4.5 to 4.7mm or, say, 1 3/4- 1 7/8 a good starting point?"

"I noticed in passing that the hammer drop seemed a little shallow (small) for my taste (4.4mm in the trichord region; 4.6m in the bass)."

Are the units here cm or mm, which measurements refer to blow and which to drop?

For blow, it would be 4.5cm or 45mm. 4.5mm would be impossible, of course. Drop should be 1mm, maybe 2mm at most. I always set to 1mm. Anything more than 2mm is just... wrong.

Do you measure drop from the string or from the let off point? Reblitz suggests let off of 1.5mm plus drop of 1.5mm making a total drop height of 3mm (1/8") below the string.

From let off.

Now set aftertouch and you're done?

Then there are those wonderful pianos where the string height decreases in a shallow arc across the capo section.
Some will regulate a straight hammer line and decrease key dip to compensate while others will maintain constant key dip and lower the hammer line to maintain blow distance.

Did I say "drop"!! I meant "blow distance"!! And not "mm" but of course "cm" (centimeters)!!

Sorry for the confusion.

Sorry. Centimeters!! (Not mm.) And I'm not talking about drop; I meant hammer blow distance! Typing faster than I ought to!!

Everything Mike says about the triangle nature of adjusting the hammer line makes perfect sense.

My question was really more about whether the Rebliztian suggestion that blow distance--for the modern concert grand--should sit ideally between 1 3/4" and 1 7/8" is still considered pretty accurate, these days. You hear reports of new grands having blow distances from the factory of 4.4 CM or less, which seems awful small!

Also, I suspect just from common sense, certainly not from any professional experience, that one would aim towards a greater blow distance (towards the 1 7/8) as long as let-off and after touch are preserved. Seems to me that one gets in this way both power and subtlety--if everything else is OK.

Now my piano is in a small room; so here's what I think might be an exception: if I push the blow distance to 1 7/8", this grand gets quite loud. Fine--great--in a concert hall; but not in a small room. So I'm playing with something in the range of 1 3/4".

A real discovery for me was the fact (as I said above) that the string height actually varies from section to section, and even within sections!! Sure, the wound strings will vary in thickness: that's obvious. But I had no idea that I couldn't just set the trichord hammer line smooth from top to bottom (although that's the way it came from the factory.)

44mm is fine for blow, depending on your other regulation specs. In fact, that is more or less my default, but, I also set my key dip somewhat more shallow than some, I suspect.

Thanks... that's exactly the sort of info I'm looking for.

JG