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TECHNICAL^SUPPIY DEPARTMENT
William Braid White, Technical Editor
spectivt-ly. This can be done in various ways.
The Widney Resiliometer measures both these
factors by a direct reading dial. Hardness is, of
course, the measure of resistance to penetra-
tion, and if the thickness of a piece of felt be
The Quantitative Elements Which Are Essential to a Proper Discussion of the Ham- carefully measured before and after it has been
subjected to a pressure of constant value, we
mer Problem in Its Relation to the Final Tonal Result in the Piano
can obtain a hardness percentage. Thus, if a
N discussing the operations of mechanisms, its maximum, almost any probable combina- piece of felt is measured as 0.05" and then under
of whatever kind, it is always important to tion of relative strengths of the other partials pressure the thickness falls to 0.25", it may be
state all facts in mathematical language, will produce a tone quality pleasing to some called 50 per cent hard; i.e. its hardness per-
where this is possible, or at least to make use ears; so that the actual mixture in any case centage is 50-
Resiliency
of quantitative rather than qualitative terms. In need not be discussed dogmatically. On the
Resiliency,
on
the
contrary, is the measure of
the course of some recent articles I have talked other hand, it is also clear that in any acceptable
about the piano hammer and its construction, tone quality the second and third partials must die ability of the resilient material to return to
but have been obliged so far to confine myself also be strong, in fact very strong. We may its original thickness after compression. It is
to generalities, at least to the extent that my therefore regard the quoted ratios as providing evident that if a piece of felt, which has been
recommendations have been qualitative. Is there us with a valuable and practical quantitative compressed under the constant weight, is found,
upon removal of the weight, to return to some
then any basis from which we can build up a basis for calculating other elements.
quantitative analysis of the elements which to-
It is now evident that if a given ratio be- ascertainable thickness less than its original
gether make up the hammer If we can find any tween contact time and vibration period be thickness, its resiliency is thereby measureable
such quantitative basis, we can then do some- adopted, we must next discover, if we can, some as a percentage.
Obviously the relation of hardness to resil-
thing to put the actual practice of hammer mak- means for defining this contact time and con-
ing upon a more scientific basis.
trolling its length. In the experiments men- iency, after these properties have been quan-
The hammer-makers will not object to such tioned this was done by photographing a piano- titatively measured, now becomes very im-
substitution of quantitative for qualitative an- forte string and hammer during the stroke and portant.
Under the system of hammer treatment to
alysis. On the contrary, they will undoubtedly causing the photographic plate simultaneously
be much better pleased to be able to feel that to take the trace of a vibrating tuning fork, so which I have alluded in previous articles, it is
a way may be opened up through which the that the actual time of the contact could be cal- evident that the hammer becomes in effect a
hard outer skin above a resilient cushion, so
pianoforte maker can place his specifications culated by comparing the number of traces of
upon a foundation of measurement. There is no the fork, of which the vibration speed is con- that the first-named property—hardness—be-
physical reason of insuperable potency forbid- stant and known. It is evident from the re- comes more important for the surface, just as
ding us to apply to the pianoforte hammer milts obtained that a pianoforte hammer strik- the property of resilience becomes more im-
quantitative tests at least as nearly accurate as ing, say, the string, may rebound from the wire portant for the inner cushion. It must there-
fore be evident also that if we accept both the
those we have already been able to apply to the in not more than either l/260th or l/520th of
one second, the frequency of the string at stand- tonal ideals which I have so often set forth and
pianoforte string.
Quantitative values for the pianoforte ham- ard pitch being 261.6 vps. It then becomes a which have recently again been obtaining ex-
mer may indeed be made in at least five differ- question of ascertaining what quantitative prop- pression through the articles in this department
erties of resilience and hardness will endow a on scale design, and the system of hammer
ent directions, as follows:
hammer, other things being equal, with the ireatment which I have also recommended for
Five Quantitative Elements
the purpose of putting the necessary finish to
power or rebounding in one of these times.
(1)—The resiliency of the hammer stem.
(2)—The hardness of the felt.
So far, this all confirms the argument prev- the tonal results thus planned for, the establish-
(3)—The resiliency of the felt.
iously made to the effect that the best internal ment of a definite relation between the resil-
(4)—The ratio of hardness to resiliency, i.e., condition of a hammer is the condition of re- iency and the hardness of the hammer becomes
(2) to (3).
latively soft cushion below relatively hard sur- practically possible.
Table of Ratios
(5)—The relations between the above proper- face. But there is much more than this to be
Using the scale of percentages previously
ties as quantitatively expressed, to the considered. For it is now a matter of realizing
parallel properties of the struck string.
that the contact time will depend in any case mentioned in connection with the Widney
It will be remembered trmt in a recent article upon (1) the hardness factor, (2) the resiliency machine, a tentative table or ratios may be out-
I quoted the results of experiments showing factor and (3) the ratio of these to each other. lined, as follows:
(Continued on /vu/r 36)
that the optimum vibration form executed by It will also be affected by the resiliency factor
a struck pianoforte string, as regards for- of the hammer stem and by the stiffness of the
mation of partial tones, occurs when the dura- strings.
tion of the contact made by the hammer upon
Methods of Measurement
the string is either equal to or one-half of the
Plainly then, the first thing to be done in an
free period of vibration of the string. If that investigation of this kind is to ascertain quan-
Associate, American Society of Mechanical
means anything at all, it means among other titative values for hardness and resiliencv re-
Engineers; Chairman, Wood Industries
Division, A. S. M. E.; Member, American
things that the hammer must rebound more
Physical Society; Member, National Piano
quickly as the strings grow shorter, since their
Technicians' Association.
vibration periods are inversely as their lengths,
EASY TO REPAIR
vvhich again means that the common practice of
Consulting Engineer to
DAMAGED FINISHES
making the treble hammers harder than the bass
OU can easily repair the damage
hammers is correct.
the Piano Industry
to varnished surfaces through fol-
But it is evident that this deduction as to an
lowing the instructions given in our
Tonally and Mechanically Correct Scales
book "How to Repair Damage to Var-
optimum ratio must lead us farther. The ex-
Tonal and Technical Surreys of Product
nished Surfaces." Dealers everywhere
periments quoted did" not attempt to show that
Tonal Betterment Work In Factoriec
are enthusiastic over the ease with
any given set of relations of value among the
which this is done—and the losses
Reference* to manufacturers of unquestioned
group made up of fundamental first, second and
which have been eliminated. A copy
position ia industry
will be sent to you free upon request.
third partials was to be preferred from the view-
point of value in tone quality. But we already
For particular!, address
know that a strong fundamental is a prerequisite
209 South State Street, CHICAGO
1OO8 W. 8th St.
Kansas City, Mo.
to good tone and that if the fundamental be at
Quantitative and Qualitative Terms in
Analyzing the Piano Hammer Problems
I
William Braid White
Y
The M.L.Campbell Co.
Punchings
Washers
Bridle Straps
5814-37th Ave.
George W. Braunsdorf, Inc.
Direct Manufacturers nf
TUNERS' TRADE SOLICITED
Piano Tuners
Also—Felts and
Cloths, Furnished
In Any Quantity
Woodside, L. I., N. Y.
35
and Technicians
are in demand. The trade needs tuners, regu-
lators and repairmen. Practical Shop School.
Send for Catalog M
Y. M. C. A. Piano Technicians School
1421 Arch St.
Philadelphia, Pa.