Music Trade Review

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37
The Music Trade Review
APRIL 23, 1927
The Technical and Supply Department—(Continued from page 36)
the tube is hooked up near the ceiling. The rate develop its vibratory movements and to start the
of travel is so slow that you can easily follow reflection which we have here witnessed.
it and even count the number of times it re-
Tension and Vibration
peats itself. For you will notice that one stroke
"If, too, I slacken tension still further, you
is sufficient to produce a large number of wave will see that the tube has a tendency to break
movements back and forth on the tube. If itself up into a still larger number of segments.
you examine the matter with some care you will On the other hand, if I now take up the slack
see that this is due to the original wave of mo- and begin to stretch the tube, precisely the op-
tion, when it reached the other end, having posite effect is noted. The number of the seg-
been once reflected back to where it came from. ments is at once reduced and you will see that
This fact of reflection is common to all cases a time comes when the tension is great enough
of stretched strings, and the stiffer and more to prevent the tube from breaking up into more
rigid the material of which the string is made than two segments. This relation of tension to
the more readily will any wave of motion im- segmentation is really very important.
parted to it be reflected from one end to the
"I need scarcely tell you that the segments
other.
into which the string breaks up correspond to
the well-known partial tone series of fundamen-
Reflection and Node
"I now make an effort to impart a second tal, octave, twelfth, second octave, etc. Nor need
stroke to the end I hold exactly at the moment 1 do more than remind you that tone quality
when the impulse from the first stroke has or color is entirely determined in the case of
reached the other end of the tube and is start- any string by the number, relative prominence
ing back. When I do this I at once cause the and intensity of these partials as they appear
wave of motion leaving my hand to meet the in any case.
Scaling
wave of motion reflected from the other end in
"All this, of cour.se, is decisively important in
the middle of the tube. Seeing that the two
waves have substantially equal power, neither scaling the strings of the piano. You are all
can obliterate the other, so that they are obliged aware that the pitch given out by a stretched
to divide up the territory between them. The musical string varies as its length, its tension
tube then divides in half each of the waves of and its weight. It is evident that if we desire
motion now traveling back and forth over one- to obtain a certain tone quality we must work
half of the total length and leaving between to learn the precise effect upon that quality
them a very sTiort but very plainly seen neutral likely to be exerted by changes in tension at
territory of minimum motion, which in fact ap- which strings are stretched, as well as changes
in dimension.
pears to be entirely at rest.
"And I now remind you that the previous
"You will also notice that the velocity of each
wave remains the same, but that owing to the simple experiment carried the lesson that in-
shorter distance each has now to travel the crease of tension discourages the ready break-
number of reflections in any given time is in ing up of a string into segments. Increase of
tension, therefore, .tends to give us stronger
each twice as great as it was before.
fundamental and fewer partial tones. For this
Segmental Vibration
"If now I proceed to strike more rapidly, you reason, in the bass sections of the piano, where
will see that soon I can cause the tube to break it is above all necessary to have strong root
up in three, four, five, six and more equal sounds, higher tension is advisable. On the
parts, each vibrating at a speed commensurable other hand, in the treble sections, where it is
inversely with its length and, of course, at the
same speed as its adjacent segments of the same
length. And you will notice at the same time
that the successive shocks imparted to the in-
ert, slackly held tube cause the segments into
which it breaks to vibrate in a manner which
exactly reproduces the form of the diagrams of
"string vibrations which you have seen in text-
books; that is to say, a series of ovals of which
the axes are lines representing the normal line
of rest of the tube.
"In order to evoke this phenomenon it is
necessary for me to impart many blows to the
tube, but if this were a steel string instead of
a slack rubbed tube one stroke would be suffi-
cient to set into motion exactly the same train
of segmental vibrations as you are now observ-
ing. And you will find that every form of musi-
cal string, short or long, steel, gut, brass, or
whatever it may be, behaves just like this. In
short, every musical string, when once set into
vibration, takes up a series of very complex
movements, which begin just as soon as the
whole length of the string has had time to
FAUST SCHOOL
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Tuners
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OTTO R. TREFZ, JR.
2110 Fairmount Ave.
Phila., Pa.
necessary that the tone quality should be bright
and sparkling, it is generally advisable to lower
the tension and thus permit the strings to sub-
divide themselves more readily.
"These statements are general in their nature.
I merely mention in passing that the choice of
striking point is also decisive in the control of
tone color. The upper strings are short, and for
them to vibrate easily in segments is difficult, if
not impossible, at any tension within which they
can act with musical efficiency (tension must
never be low enough to make the stiff steel wire
too flexible). Hence the striking point is
brought progressively nearer to one end of the
string, so that the propagation of partial tones
may be artificially stimulated.
"Now you can easily see that the point of
stress at which a piece of piano wire breaks
should always be determined with reference to
the tension at which it is to be used in practice.
Here emerges the question of elastic limit. If
we find by experiment that a tension of so
many pounds upon a string of given length and
other properties gives us a desired quality of
tone, than we should use for that string a wire
of which the elastic limit is about twice as high.
The limit of tensile resistance is always slightly
above this point of strain at which the string
ceases to be elastic and takes a permanent elon-
gation. To choose a wire merely because its
breaking point is at so many pounds is not sci-
entific. What is needed is to find the wire that
will produce the required effect at a given ten-
sion. It may be taken as axiomatic that this
wire, whatever it be, will always fall within the
rule as to clastic limit laid down above.
"The question of hardness of the steel comes
in here, too, incidentally,or it is bound up with
the question of elastic limit and breaking strain.
Wire may be drawn to any hardness or almost
any elastic limit, but the question is what tone
will any given type of wire give. And no other
question than this is of the slightest importance.
(Continued on page 38)
Tuners Carrying Case
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Outside measurements 15J4 inches long, 7
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When closed the aluminum
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New York Since 1848
4th Ave. at 13th St.