Why don't the hammers..

fumbler · Post by **fumbler** » 17 Mar 2005, 20:04

Hi,

I don't know where all these questions come from. Why do the hammers strike the strings at the top of their speaking length? All practicalities to one side for a moment, why don't the hammers hit the strings in the middle, or close to the middle, of their span? Would the sound be better, or worse?

Thinking as I type, perhaps the bass would be uncontrollable...

Rgds.

Brian Lawson, RPT · Post by **Brian Lawson, RPT** » 17 Mar 2005, 20:21

Simply put, it would sound worse. You would notice that the hammers are positioned in a straight line (strike line) where they hit the stings. It is a point worked out be the designer to be the optimum point to get the best harmonics from the string. Proportionally where the top hammer hits the short string is relatively the same as where the subsquent lower hammers hit on progressively longer strings.

classic-keyboard · Post by **classic-keyboard** » 17 Mar 2005, 21:44

Sticking my foot in my mouth... when a string vibrates, it doesn't just vibrate at the fundemental, it also vibrates at higher frequencies (i.e. partials). At the fundemental there's a node at each end of the string. The first partial has a node in the centre of the string i.e. double the frequency but it also vibrates with 2 nodes, 3 nodes, 4 nodes etc. Some of these are more undesireable than others. The point the hammer hits the string can be a node

The hammer is set to hit the string at a point which as far as possible discourages undersirable partials and encourages desirable ones.

A440 · Post by **A440** » 02 Jul 2005, 02:25

1 sixth of the speaking length seems to be (more or less) the correct strike point, Like any machine it's all compromise and no machine is 100% efficient...

fumbler · Post by **fumbler** » 02 Jul 2005, 11:42

Hi,

Thanks for all the interesting responses. I'm not sure I really buy the partials answer. For the hammers to strike on the nodes of the partials would require exquisite accuracy which you just couldn't get in a piano action. And missing by a fraction would produce a worse sound.

I'm sticking to practical reasons. If the hammers hit in the centre the impact would be absorbed by the greater 'give' of the strings, and with the greater resonance the dampers would be shaken off the strings. But I'm open to more ideas.

Rgds.

PianoGuy · Post by **PianoGuy** » 02 Jul 2005, 11:48

fumbler wrote:Hi,

Thanks for all the interesting responses. I'm not sure I really buy the partials answer. For the hammers to strike on the nodes of the partials would require exquisite accuracy which you just couldn't get in a piano action. And missing by a fraction would produce a worse sound.

Buy the partials idea matey, cos your idea is plain wrong!! An interesting theory though. See my final comment.

Why couldn't one get this accuracy in a piano action then? I bet you're a bloody mechanical engineer.

fumbler · Post by **fumbler** » 02 Jul 2005, 12:05

[quote="PianoGuyI bet you're a bloody mechanical engineer.[/quote]

No, but I probably should have been. My reasoning (which I readily accept may be incorrect) is that the node for (say) the first partial is exactly on the half-way point of the string (I'm ignoring petty details). How inaccurate can it be before the partial is incorrect and sounds wrong? A few microns? Half a millimetre? I'd say somewhere between these two, and no wooden (or ABS) piano action will get this accuracy.

It's the same as the frets on a guitar. How inaccurately can these be machined before the note produced is wrong? Not far I would say.

The hammers will hit a partial of some sort, but not necessarily one of the important (i.e. heard) ones.

Rgds.

PianoGuy · Post by **PianoGuy** » 02 Jul 2005, 12:20

Granted, but the surface area of a hammer contacting with a string is sufficiently large to cover that point (and a bit either side!), the hammer being made of felt and constructed so that it's highly elastic, yet sufficiently resilient.

As the hammer becomes worn and grooved, more partials are suppressed until in the case of a severely grooved hammer, the hammer literally acts as both hammer and damper.

Best!

PG

Post by **Gill the Piano** » 02 Jul 2005, 19:25

O dear God, don't let 'em start on the ABS again...I don't think me nerves will take it...

Post by **Barrie Heaton** » 03 Jul 2005, 11:57

fumbler wrote: No, but I probably should have been. My reasoning (which I readily accept may be incorrect) is that the node for (say) the first partial is exactly on the half-way point of the string (I'm ignoring petty details). How inaccurate can it be before the partial is incorrect and sounds wrong? A few microns? Half a millimetre? I'd say somewhere between these two, and no wooden (or ABS) piano action will get this accuracy.

We are taking Harmonics and it is the 7th in particular that you would like to kill
to do this you need to hit it on the node killing it and emphasising the Anti nodes of the other harmonics, in the bass because if the size of the string you have quite a margin of error in the top treble you don't a target area of about 0.5mm this is very easily achieved with the hammer. However, the trick is not to kill the the second, third and forth harmonics That is why we
paper new hammers to modify the shape to get the sound we need.

A simple test is pluck a string and touch it is the centre you with hear the
second harmonic being emphasised

Action makers have been working to a tolerance of 100th of a Millimetre for
centuries

take a pair of callipers and measure the width of a good set of hammers and
you will be amassed how accurate they are

Barrie,