Piano World Home Page Forums Our Most Popular Forums Piano Tuner-Technicians Forum Dissecting the Tone of Piano Hammers

The nonlinear spring allows color change with volume change. With a soft blow, the hammer is compressed a relatively small amount, and hence stays within the low spring-force region. The relative softness at this point produces a relatively dark tone. With hard blows, the hammer is compressed into the relatively high spring-force region, and so the hammer effectively becomes harder. The harder hammer produces a brighter tone, with relatively more power in the upper partials. In hammers with a constant spring constant, harder or softer blows produce a change in volume, but not in tone.

Yes, but this is the case only for simple helical wound springs. Look at a car suspension spring, it typically has an area where the coils are wound shallowly and a larger area where the coils are more widely spaced and hence stiffer. This means that when a load comes on the spring is quite compliant and a low load compresses it easily. As those close wound coils make contact with each other they effectively become a solid lump of metal not a spring, and further compression requires the stiffer coils to compress. So effectively we have a spring that acts as two different springs of different stiffness and the overall response is not linear. This again is a simple case and much more complex non-linear compression rates can be engineered in to the design.

I think it's fair to say that springs are linear unless they contain specific design features to make them nonlinear. To look at it another way, the spring constant is proportional to the stress/strain value for the (typically) metal used in the spring. Stress/strain defines the Young's modulus of the material. The Young's modulus is constant for any given metal as long as it is used within its elastic limits. Please let me know if I misstated anything.

In other words, when less force is applied, the hammer is compressed less. When more force is applied, the hammer is compresed more. Just like a linear spring.

With a hard blow, hammer felt rebounds slower from deformation than when it delivers a lesser blow. This makes the hammer seem harder to the string when it hits the string with more force than when it hits it with less. Hence the tone is brighter when played hard than when played soft. So the tone color changes with dynamics. Just what the composer ordered.

This is why continuously felted hammers swept the industry when Henri Pape introduced them.

I believe you're missing the point--a linear spring has a constant spring constant whereas a nonlinear spring has a varying spring constant. In the latter case, the incremental spring constant is a function of the amount of compression. As such, the strings being struck experience a different spring constant as the hammer blow is varied. I believe you claim to have a math background, in which case, my post should have been simply understood by you.
This image should make it crystal clear. If the image does not embed itself in this post, the link labeled "image" seems to work fine.
[img]https://imgur.com/rDCAuCX[/img]

I don't think analogies are the best way to teach hammer voicing techniques. Its better to learn directly, for example the sound a hard shoulder makes versus a soft shoulder, or too soft a shoulder. And then having the tools to make the correct altercation. etc.

Also, Todds method is not the same old paradigm. And this may have been missed. The main feature is the spraying, and the diluted softener solution. The hairspray technique is a clever way to spray in a clients home. Whereas, in the shop i use B-72 and my small spraygun. Spraying imparts an evenness that is unparalleled compared to using a hypo or needling.

What may or may not have come across in the video, was before Todd started with the spray techniques he spent quite a bit of time teaching how to listen to the hammer. This was important because then all of us could hear the changes. That was what made this so impressive.

-Chris

No, you're exactly right. A spring made of a perfectly elastic material (which spring steel is a very close approximation to) will be linear - unless it isn't because it isn't a simple helix with uniform pitch and uniform cross section and the same material composition throughout. Other materials are of course much worse approximations to the perfect spring than spring steel and so are likely to be less linear.

Chris, don't confuse scientific models with analogies. They are not the same thing.

Describing inertial properties, spring rates and periodicity elements uses standard engineering methods. The piano industry seems to need to elaborate with models that I find distracting. I think that tendency exposes the low literacy level of the profession.

A harder blow deforms the hammer and string more than a lesser blow. It may take time to rebound just from the fact that it is a greater distance to rebound from. More information is necessary.

The point that I "missed" was the one that you failed to make, just like you failed to understand how to embed images. Of course, the image itself has nothing to do with the question. It is just a couple of graphs someone has drawn. In order for it to be relevant, one would have to show that one or the other actually pertains to piano hammers. You would also have to show several things: That either of the graphs comes from piano hammers, that if one of them does come from piano hammers that it is accurate, that it is not linear instead of just a different constant, etc.

That is before getting to the pertinent part of the discussion: What voicing techniques make a difference in the graph, and what differences in the sound do you get from the graph. Or you could skip the graph entirely and go to what voicing techniques make what differences in the sound, which is pretty much what Chris and I are concentrating on.

BDB, A harder blow from a piano hammer to a string does not deform the string in any meaningful way. It displaces the string more from rest. And of course the string is still going at the same periodic rate, so its return from displacement takes the same time regardless of displacement.

The hammer felt works differently. The felt compression returns from the deformation of a hard blow slower than it does from a lesser blow.

The distance the hammer travels with the string is a distracting way to look at it, because during hammer string contact the hammer and string are coupled. This makes the hammer inertia relation to the string periodicity the most significant factor of hammer dwell time on the string.

The short pre-digested answer is "for tone color" .

Does that mean that if the hammers had a linear force curve, there would be no tone color?

(Remembering that it is by no means clear that hammers do not have a linear force curve. So far, nobody has bothered to demonstrate whether they do or do not.)

BDB take a bass or tenor hammer and press into it firmly with the round shaft of a small screwdriver. Watch how fast the felt rebounds from that deformation. Then repeat it with a slight force and compare. If you have ever placed your hand above a grand hammer and played the key gently to where the hammer just touches your skin, that is the force the felt takes on the softest blows. It ain't much.

if I press on a linear spring a little bit, it will rebound slowly. If I press on it a lot, it will rebound faster. I would not be able to tell the difference without more equipment than I am willing to invest, however. Same results with a hammer. Same results with a piano string. Without a lot of work, I would not be able to tell whether the change is constant or a variable. Either way, I am not certain what the difference would be as concerns a piano's sound.

BDB it seems you are confusing distance with period.

How does knowing about linear or non linear springs help me with voicing a piano hammer? How do i put that to use?
-chris

It is just jargon, for the sake of making people think that they actually know what they are talking about. In the end, it boils down to what I said: Everybody has a bag of tricks that they rely on to get the sound that they can get. You have yours, I have mine. Without listening to the pianos in person, it is really hard to evaluate them.

I appreciate your sharing this bag of tricks, but I am no longer doing much shop work any longer, so I have to limit techniques to those which are quick and clean, since I am in customers' homes. I do not want to fill their houses with solvent smells. I also like to do a little voicing on low-quality pianos, to show the customer what is possible, and to educate their ears so that maybe they will want something better sometime. You can do so much for them fairly quickly, and there are a lot more of them than there are high-quality pianos. You can really improve your reputation fast by performing miracles on cheap pianos, and it keeps you in practice for the better pianos.

I do believe that the results depend on how the hammer hits the string, as well as how the hammer releases from the string, but linear versus non-linear is not the factor.

Thanks BDB,
I suppose that makes it clear regarding intellectualizing for the sake of tickling their own ears.

A quick word about chemical smell. First the hairspray, to me it isn't unpleasant. At least I never complained when i was dating. When Todd was using it, i don't recall the smell being a concern. But if it were me, I would use the B-72 instead( which the primary smell is the alcohol). What I do is put a few drops of Lavender essential oil in the B-72, and it smells very nice( or should i say quite lovely). Todd said he uses rose water. In the fabric softener solution i also put a few drops of lavender. I don't say all of this to convince you because clearly you have your tricks you're happy with, but that i too was concerned about smell. But I don't think that's a worry in this case.

-chris

Lanolin is Yellow. Abel admits that natural felt hammers have considerably more lanolin in them then acid Washed hammers. They are also a darker colored hammer. Lanolin is the natural lubricant in wool. The fabric softener simulates the lanolin and even the natural felt hammers can be improved with this method. The alcohol is the carrier that thins the fabric softener and softnens the wool all the way down to the core.

I read everything. I'm not going to argue with any of you. The techs that learn how to use this method will appreciate it. As far as I'm concerned, all good things come from God anyhow. I won't take the credit for the things that He teaches me.

Todd