Repost:StrikeWt/Ratio

[stanwood]

>From posting sent to pianotech@byu.edu  1/11/95   2:30pm



Strike Weight and Strike Ratio


To measure leverage we use a touchweight parameter called
strike ratio.

*Strike ratio is the amount of weight needed to balance
 one gram of hammer weight at the front of the key.

Strike ratio gives an indication of how fast the hammer
moves in relation to the downward movement of the key.  It
is therefore a useful indicator of the dynamic quality of
the action.  In fact we have found that the dynamic
playing quality of the action may be predicted if the
strike ratio and the hammer weight are known.  More on
hammer weight later...

The strike ratio level of a piano action is determined by
measuring strike ratio in sample keys and calculating the
average.  For minimum significant accuracy we use a sample
of six  measurements on notes 16,17,40,41,64,65.  More
accuracy is attained by measuring all the c-c#s.  Maximum
accuracy is attained by measuring all 88 notes.

*****Strike ratio is determined by finding the strike
balance weight and dividing it by the strike weight.*****

Measuring strike balance weight:

1. Lift up the hammer and shank.
2. Place temporary weights on the back of the key such
   that the balance weight of he key and wippen becomes
   zero.
3. Lower the hammer and shank back down
4. Measure upweight and downweight.
5. Calculate strike balance weight as the average of
   upweight and downweight


*Strike weight is the amount of weight that hits the
 string Measuring strike weight:

1.Remove the shank from the rail
2.place a hard felt wedge on the pan of a digital scale
  and tare to zero.
3.Place the striking surface of the hammer face down on
  the felt wedge such   that the strike line of the hammer
  is resting on the knife edge of the     felt wedge
4.Tip up the flange so that it is oriented vertically,
5.Rest the bottom end of the flange on a roller bearing
  such that the axis   of the roller bearing is aligned
  vertically with the axis of the center pin, with the
  shank perfectly horizontal.
6.The resulting scale reading indicates the strike weight.

Again: Strike Ratio = Strike Balance Weight/Strike Weight

Acceptable strike ratio levels fall in a range from 5.0 to
7.0 If strike ratio level is below 5.0 the hammer will
move too slowly in relation to the key and excessive key
dip will be required to regulate the action.  If strike
ratio level is above 7.0 the hammer will move too quickly
in relation to the key and excessively shallow key dip
will be required.

We recommend 5.5 as a modern standard for strike ratio.
The best pianos surveyed were close to this level.  The
5.5 standard emulates the Hamburg Steinway which is the
only piano surveyed that was consistently at this level
with consistently the best action.
*********************************

I offer the following range guidelines for strike weight
and strike ratio. These ranges are the result of 4 years
of survey and analysis of piano actions.

The primary touchweight studies were carried out by myself
and the following technicians:

Russell Gordon RPT
Tony McKenna, Belmont Mass
Bill Ballard RPT
John Foy RPT

                 STRIKE WEIGHT RANGE GUIDELINES:

Note   1          22          44          66          88


       14.8-------13.7-------12.1--------9.8---------6.9
         F U L L       T O N A L    P R O J E C T I O N
       12.4-------11.5-------10.2--------8.3---------5.8
         M E D I U M   T O N A L    P R O J E C T I O N
       10.3--------9.5--------8.4--------6.7---------4.6
         L O W         T O N A L    P R O J E C T I O N
        8.0--------7.4--------6.5--------5.2---------3.5

                       STRIKE RATIO RANGE GUIDELINES

Full Leverage            5.0 - 5.7
Medium Leverage          5.7 - 6.3
Low Leverage             6.3 - 7.0

We have found that if a full ,medium, or low strike ratio
is matched with a full, medium or low, strike weight a
normal feeling action will result when balanced to a
normal upweight and downweight.  Problems are likely when
ranges are mismatched.  For instance: Full  projection
weight hammers matched with low leverage will yield a
piano with high inertia that plays like a truck, or: Low
projection weight hammers matched with full leverage will
make for an action that is excessively light with low
inertia. Refer to the table below:






                       TABLE

Dynamic touch as a function of Strike Weight and Leverage
for actions balanced to an average balance wt. of 38 grams


                      Leverage

S                LOW      MEDIUM      FULL
t
r     LOW        medium    light     xlight
i
k     MEDIUM     heavy     medium    light
e
      FULL      xheavy     heavy     medium
W
t




One final note: The hammer weight may be found by
subtracting the shank strike weight from the strike
weight.  The shank strike weight is the weight of the
shank taken at the strike line radius.

Shank strike Weight is generally around 1.8 - 2.0 grams

David C. Stanwood



Copyrights reserved by David C. Stanwood June 1995
The document may not be reproduced in any without permission of David C.s
Stanwood, exceptt for print outs of this document in this form for personal
use.