Conn STROBOCONN - Page 11

STROBOCONN "PIANO TUNING" MANUAL
Figure ll-Air-borne microphone located on piano keyboard. It
may be necessary to move mike several times in order to obtain
maximum reception on the string being tuned.
Table I-A or Figure 7. For example, for A-435, set
pointer at minus 20 and for A-442 set pointer at plus 8.
Many technicians prefer to start tuning at the "break"
in the scale because of the marked change in the inhar-
mondty of the partials of the tones at this point. The
stiffness of piano strings causes the tones produced to
have partials that are not harmonically related to each
other; that is, the second partial is not exactly twice the
frequency
of the first partial, or fundamental, of the
tone.
The third partial is not three times the frequency
of the fundamental, and so on. For partials to be har-
monic they need
to bear a whole number relationship
(1, 2, 3, 4,----) to the fundamental. The partials in
piano tones are always slightly higher (sharp) than the
whole number multiples (harmonics) of the fundamen-
tal. This has a very important bearing upon the tuning
of a piano.
When listening to two piano tones an exact octave
apart, the second partial of the lower tone will be sharp
with respect to the fundamental of the higher tone. This
will cause audible beats to be produced and the listener
will not consider the tones to be truly an octave apart
even though the fundamental frequency of the top tone
is exactly twice the fundamental frequency of the lower
tone, as is required for a true octave. In order for the
octave
on the piano to sound in tune when the two
no:es are played at the same time, it is necessary to
lstretch the interval by lowering the bottom tone or
raising the top tone. The technique for determining
the optimum amount of stretch with the Stroboconn will
be
explained as we go along.
The inharmonicity of piano tone partials is usually
smallest
in the middle of the keyboard so an octave is
chosen
there for setting the temperament. Care should
be taken that the "break", or a marked change in string
design, does not occur within the temperament octave.
All but one string per key is muted with felt or
wedges so only one string at a time sounds when a key
is struck.
Let us assume
that C4 (middle C) is chosen for the
starting point as an example. Some other starting point
might be preferred and could be used as well. Proceed
from C4 up the scale, tuning one string on each key
while
watching the fourth ring, or pattern band, in the
appropriate windows. The Stroboconn pointer is left in
the position chosen to establish the tuning standard
while tuning this octave.
It may be noted while tuning this octave that even
though the tension on the string is adjusted to cause the
fo.urth ring pattern to be stopped, the patterns in the
fifth and higher rings will move slowly to the right due
to
the fact that the partials producing those patterns
are not exactly in a 2, 4, 8----- relationship to be funda-
mental of the tone. If the fifth ring pattern moves to
the right for the C
4
string, when the fourth ring pattern
is not moving, ·the tuner can note how far to the right
he needs to move the Stroboconn pointer in order to
make the fifth ring pattern stand still. If this is one cent
or more, it indicates that Co should be tuned sharp by at
least that amount. Therefore, when tuning C, the point-
er is advanced to the right of the s:arting position used
for tuning the temperament octave. This is the begin-
ning of the octave-stretching process.
.
The fundamental is usually the strongest partial in
the tones above C4, and the higher partials are progres-
sively weaker.
Thus, the fundamental and the second
partial are the two most important parts of the tone to
consider when tuning octaves. However, the meticulous
Figure 13-"Stretching" First Octave.
To "stretch" the first oc-
tave, read the pattern
made by the overtones
in the 3rd octave band.
To "stretch" the 2nd or
3rd octave, read the
pattern made by the
overtones in the 4th
octave ba nd.
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Figure 14-"Stretching" 2nd and 3rd octaves.