Music Trade Review
Issue: 1932 Vol. 91 N. 4 - Page 18
Music Trade Review -- © mbsi.org, arcade-museum.com -- digitized with support from namm.org
PIANO FACTORY and
PIANO SERVICING
DR. W M . BRAID WHITE
Technical Editor
,
Some Points on
The Analysis of
Tone Vibrations
DR. WM. BRAID WHITE
I
HAD actually started to write, and was
well on in, a discussion of quite another
kind for this month's contribution, when
a letter arrived from Mr. Roy Elliott, of
Hammond, Ind., who disclosed some questions
of such general interest that I felt I could do
nothing else so useful for THE REVIEW this
month as to answer them forthwith. So here
they are, with my answers:
1. How or by what method are the vibra-
tions of a tuning fork counted, so as to de-
termine an exact number per second?
Answer. There are several possible meth-
ods.
I may begin with one very simple
scheme. Suppose that a very light needle be
attached to one prong of a tuning fork. Now
let the fork be held so that this needle stands
with its point downwards, upon or just above
a table, so that when the fork vibrates the
needle must move transversely back and
forth over this surface. Now let a strip of
smoked paper be caused to move underneath
the path of the needle at a definitely known
and constantly maintained rate of travel. If
now the fork be started vibrating the needle
will trace out a wavy or undulating line on
the smoked paper. If the speed of travel of
the paper be known, then the number of the
wavy lines in any given length will indicate
by a simple calculation the speed of vibration
of the fork. For, if the strip of smoked paper
move at the rate of, say, four feet per second,
then in four feet of the paper's length there
will be recorded the vibrations during one sec-
ond of motion by the fork. If the number of
these waves or undulations so recorded be
+40, in four feet of paper, then the speed of
the fork will be 440 per second. And so on.
Another and more accurate method is to
make the fork part of a magnetic system by
placing one of its prongs between the poles
of a suitable magnet. If now the fork be
vibrated while a direct electric current is
flowing through it, the resulting changes in
the magnetic flux can be registered upon a
string-and-mirror galvanometer. If now the
mirror of the galvanometer be suitably illu-
minated, its motions can be recorded photo-
graphically upon a film moving at a known
and constant speed. The recorded undulations
may then be counted and the fork's speed
rated as before.
Another and better method has been util-
ized with great success and remarkable ac-
curacy by Dr. Dayton Miller, of Cleveland.
In this method use is made of the famous
tuning-fork clock of Koenig, as improved by
Doctor Miller. Here, a clock is furnished
with a pendulum which, in fact, is a tuning
fork vibrating 64 cycles per second and
very accurately rated. By suitable reduction
gearing this fork is caused to control the
clock in the ordinary way just as any pendu-
lum would. There is a special second hand
attached to the tuning fork in such a manner
that it makes one complete revolution around
the face of the clock every second, being con-
trolled by the fork, which runs at 64
complete vibrations or 128 oscillations per
second. The clock is now set running and
of
OF
BUCKSKIN.
T h e MOORE a n d FISHER Manufacturing Co.
Deep River, Conn.
THE
Estate
/HANUFACTORER
WHERE CAN YOU GET
PLAYER ACTION
REPAIRS and SUPPLIES
18
compared carefully with a standard clock.
The rate of the tuning fork is corrected by
sliding weights on it. If the clock is found
to be keeping perfect time then it is known
that the tuning fork pendulum is making
actually 128 oscillations per second, no more
and no less.
Suppose now it be desired to rate a fork
to 440 vibration cycles accurately. Since the
tuning fork pendulum is making 64 cycles
or 128 oscillations normally, we make a cal-
culation and find that the number 7 is the
one that goes into 440 with a quotient near-
est to 64. That quotient is actually 62.85.
By an equally simple calculation we see that
if we are to make the clock fork run its
pendulum at one-seventh of 440, or 62.85
times per second, rather than at 64, it must
be adjusted to lose 1 minute 4.8 seconds in
each hour. The adjustment is made, and
tested for correctness by a standard clock.
The vibration of the fork under test is
then watched through a microscope attached
to the clock fork. A bit of chalk on the end
of the fork prong makes this easy, especially
if it be illuminated brightly. When the two
forks (clock and fork under test) are then
set into vibration together, the clock fork
should be running at just one-seventh the
speed of the other. If this is actually so, then
the interposition of the slow upon the fast
vibration will cause the illuminated bit of
chalk dust to appear to the eye through the
microscope as a figure of the kind first
1049—3rd St.
NORTH BERGEN. N. J.
Tel.: 7—4367
MUSIC
TRADE
REVIEW,
A p r i l , 1932
PIANO FACTORY and
PIANO SERVICING
DR. W M . BRAID WHITE
Technical Editor
,
Some Points on
The Analysis of
Tone Vibrations
DR. WM. BRAID WHITE
I
HAD actually started to write, and was
well on in, a discussion of quite another
kind for this month's contribution, when
a letter arrived from Mr. Roy Elliott, of
Hammond, Ind., who disclosed some questions
of such general interest that I felt I could do
nothing else so useful for THE REVIEW this
month as to answer them forthwith. So here
they are, with my answers:
1. How or by what method are the vibra-
tions of a tuning fork counted, so as to de-
termine an exact number per second?
Answer. There are several possible meth-
ods.
I may begin with one very simple
scheme. Suppose that a very light needle be
attached to one prong of a tuning fork. Now
let the fork be held so that this needle stands
with its point downwards, upon or just above
a table, so that when the fork vibrates the
needle must move transversely back and
forth over this surface. Now let a strip of
smoked paper be caused to move underneath
the path of the needle at a definitely known
and constantly maintained rate of travel. If
now the fork be started vibrating the needle
will trace out a wavy or undulating line on
the smoked paper. If the speed of travel of
the paper be known, then the number of the
wavy lines in any given length will indicate
by a simple calculation the speed of vibration
of the fork. For, if the strip of smoked paper
move at the rate of, say, four feet per second,
then in four feet of the paper's length there
will be recorded the vibrations during one sec-
ond of motion by the fork. If the number of
these waves or undulations so recorded be
+40, in four feet of paper, then the speed of
the fork will be 440 per second. And so on.
Another and more accurate method is to
make the fork part of a magnetic system by
placing one of its prongs between the poles
of a suitable magnet. If now the fork be
vibrated while a direct electric current is
flowing through it, the resulting changes in
the magnetic flux can be registered upon a
string-and-mirror galvanometer. If now the
mirror of the galvanometer be suitably illu-
minated, its motions can be recorded photo-
graphically upon a film moving at a known
and constant speed. The recorded undulations
may then be counted and the fork's speed
rated as before.
Another and better method has been util-
ized with great success and remarkable ac-
curacy by Dr. Dayton Miller, of Cleveland.
In this method use is made of the famous
tuning-fork clock of Koenig, as improved by
Doctor Miller. Here, a clock is furnished
with a pendulum which, in fact, is a tuning
fork vibrating 64 cycles per second and
very accurately rated. By suitable reduction
gearing this fork is caused to control the
clock in the ordinary way just as any pendu-
lum would. There is a special second hand
attached to the tuning fork in such a manner
that it makes one complete revolution around
the face of the clock every second, being con-
trolled by the fork, which runs at 64
complete vibrations or 128 oscillations per
second. The clock is now set running and
of
OF
BUCKSKIN.
T h e MOORE a n d FISHER Manufacturing Co.
Deep River, Conn.
THE
Estate
/HANUFACTORER
WHERE CAN YOU GET
PLAYER ACTION
REPAIRS and SUPPLIES
18
compared carefully with a standard clock.
The rate of the tuning fork is corrected by
sliding weights on it. If the clock is found
to be keeping perfect time then it is known
that the tuning fork pendulum is making
actually 128 oscillations per second, no more
and no less.
Suppose now it be desired to rate a fork
to 440 vibration cycles accurately. Since the
tuning fork pendulum is making 64 cycles
or 128 oscillations normally, we make a cal-
culation and find that the number 7 is the
one that goes into 440 with a quotient near-
est to 64. That quotient is actually 62.85.
By an equally simple calculation we see that
if we are to make the clock fork run its
pendulum at one-seventh of 440, or 62.85
times per second, rather than at 64, it must
be adjusted to lose 1 minute 4.8 seconds in
each hour. The adjustment is made, and
tested for correctness by a standard clock.
The vibration of the fork under test is
then watched through a microscope attached
to the clock fork. A bit of chalk on the end
of the fork prong makes this easy, especially
if it be illuminated brightly. When the two
forks (clock and fork under test) are then
set into vibration together, the clock fork
should be running at just one-seventh the
speed of the other. If this is actually so, then
the interposition of the slow upon the fast
vibration will cause the illuminated bit of
chalk dust to appear to the eye through the
microscope as a figure of the kind first
1049—3rd St.
NORTH BERGEN. N. J.
Tel.: 7—4367
MUSIC
TRADE
REVIEW,
A p r i l , 1932
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