I'm very curious about the enormous tonal diversity of a piano. Most of it is originated by the hammer.
I would like to know more about the piano hammer structure, specifically on the bass notes:
- Area of the hammer responsible for sound intensity?
- what is the characterist of the felt that makes it punchy?
- what is the role of the hammer shoulder in the tone?
- what is the role of the hammer crown in the tone?
Comments and personal experience are welcome.

Could I add two points to that list?
- effect of underfelt/no undefelt
- the thickness of the wood moulding around which the felt is wrapped in the top treble. Specifically, on old german grands, all the original hammers I've seen had incredibly thin mouldings, around 3mm. The newer hammers which I've seen all look around 4-5mm.
Do they not like making delicate hammers, or do they exist?
James

I would not consider that most of the tone originates from the hammer. The scale design and soundboard assembly design also greatly contribute. The hammer cannot bring out tone that is not there to begin with.
In the bass I would say that sound intensity is related to hammer mass. It takes a massive hammer proportional to the mass of the bass string it is trying to move.
Not certain what you mean by punchy but the higher quality hammers have felt that is carefully treated from sheep to press. The felt is probably not washed with chemicals that damage felt fiber and the hammer sets are cold pressed. The hammer felt retains its resiaiance.
If the shoulder is too soft it will rob energy from the string. The crown will effect the entire tonal range.
I am certain that someone else can elaborate on this much more than me.
There is much to read about hammers and hammer string interaction. Don Hall from Sac State University has written about it in "The Five Lectures" http://www.speech.kth.se/music/5_lectures/contents.html
or Dr Russell at Kettering University http://www.kettering.edu/~drussell/hammers.html
There is also a discussion about the subject in the book that Del Fandrich resurected "Piano Tone Building" at the to of this forum.

- Area of the hammer responsible for sound intensity?

The part that hits the string.

- what is the characterist of the felt that makes it punchy?

Alcoholism?

- what is the role of the hammer shoulder in the tone?

Connecting the action to the part that hits the string.

- what is the role of the hammer crown in the tone?

It is the part that hits the strings.

If you want a serious answer, you need to study the wave equation as a differential equation. Basically, it says that the shape of the wave, which determines the harmonic content, depends entirely on the initial conditions. That is the shape of the string when it displaced and released. The hammer is entirely responsible for that, in its shape, hardness, elastic characteristics, and the point where it hits the string.

It is something you should learn by training, after a little understanding of the basics which are that the hammer only can help the sound in regard of a particular soundbord setup and condition.

A good way to learn is to change hammers on a grand piano .

There are seminars and trainings in France organized regularely. have a look at the AFRP web Site if you wish to attain.

To have some benefit of a hammer change training, one may have undestood the precise (I mean musical) regulation of the grand.

Al in all that could take a few years (5 to 10) if you are not training dayly (and more than that !

The hammer felt is a thick sheet of progressively harder felt which is plied on a wooden core, compressed, and secured with glue and an agrafe.

The way to treat them is differnet depending of the era, the kind of hammer, the continent, and the wanted tonal output.
ANd more than that is is mostly a cuultural question to begin with , as you need to have a good picture of what you are looking for before discovering waht is really possible on a given instrument.

All descriptions can't help much, we are tempted to siplify and to have rules, but even those rules may differ depending of the factory.

An experienced tuner and regulating technician can
easely understand voicing, some are more likely to do so than others.

Modern hammers are alwaus thicker in the treble, older one tend to warp in time, or sometime break unde rthe press pressure, hammer makers dont take the risk actually.

The wood within the hammer play a role in the attack tone as it load the shank and resonnate with it (hence insertion of lead always kill part of that aspect)in fact everything in a piano have some importantce , even the pianist !!!

BDB:

Thanks for that explaination! That makes a lot of sense.