-Note that these ratios produce a very close *approximation* of the equal tempered scale. They are *NOT* exact. These ratios are used in each of the first seven octaves. The octave produced is dependant
on the number of teeth on the ToneWheel''''s. In 60Hz
organs, the motor turns at 1200 RPM / 60Hz or 20 revolutions per second. The lowest octave has tonewheels with 2 teeth. The first 7 tones in the highest octave (C through F#) are produced by tonewheels with 192 teeth. For these 7 tones to be correct with only 192 teeth, they use the gear ratios for notes F through B.
+Note that these ratios produce a very close *approximation* of the equal tempered scale. They are *NOT* exact. These ratios are used in each of the first seven octaves. The octave produced is dependent
on the number of teeth on the ToneWheel''''s. In 60 Hz
organs, the motor turns at 1200 RPM / 60Hz or 20 revolutions per second. The lowest octave has tonewheels with 2 teeth. The first 7 tones in the highest octave (C through F#) are produced by tonewheels with 192 teeth. For these 7 tones to be correct with only 192 teeth, they use the gear ratios for notes F through B.
The formula to calculate the exact frequency produced is:
<verbatim>
(Motor RPM/60)*Teeth in Toneweel*(Teeth in Driving Gear/Teeth in Driven Gear)
-So for A-440
on a 60Hz
organ: (1200/60) * 16 * (88/64) = 440Hz
+So for the
A above middle C
on a 60 Hz
organ: (1200/60) * 16 * (88/64) = 440 Hz
-The A notes are
the only notes
on the Hammond which agree
exactly with the
equal tempered scale
. The notes which are the farthest off pitch in the first seven octaves are the G#. They are .69 cents flat from the correct pitch. The top half octave is farther off pitch due to the number of teeth on the tonewheel not equaling 256. Using 192 teeth, generating the correct pitch from C7 to F#7 requires using the gear ratios for F through B. In the top half octave, the C# is the farthest off pitch, about 1.93 cents sharp:
+This A tonewheel frequency actually influenced the establishment of the commonly accepted concert pitch standard as 440 Hz. Historically, concert A has wandered between 430-450 Hz.
The famous Stroboconn tuner was introduced in 1936 and copied Hammond's use of an AC mains driven synchronous motor spinning an optical disk that also set the
A above middle C at 440 Hz. Within a couple of years, Stroboconn tuners were being used globally to help tune concert orchestras. By 1939 enough orchestras had set their concert pitch to
the A of the Stroboconn (and the Hammond) that the international concert pitch standard of A = 440 Hz was established.
+
+None of the twelve semitones
on the Hammond are
exactly equal tempered in their relationship to each other
. The notes which are the farthest off pitch in the first seven octaves are the G#. They are .69 cents flat from the correct pitch. The top half octave is farther off pitch due to the number of teeth on the tonewheel not equaling 256. Using 192 teeth, generating the correct pitch from C7 to F#7 requires using the gear ratios for F through B. In the top half octave, the C# is the farthest off pitch, about 1.93 cents sharp:
-For C#-4434: (1200/60) * 192 * (74/64) = 4440Hz
+For C#-4434: (1200/60) * 192 * (74/64) = 4440 Hz
