Differences between current version and predecessor to the previous major change of LoudnessRobbing.

Other diffs: Previous Revision, Previous Author

Newer page: version 7 Last edited on May 18, 2008 9:31 pm. by JimCook
Older page: version 6 Last edited on April 9, 2008 1:09 pm. by JimCook
@@ -9,11 +9,11 @@
  * the distance between the magnet and the tone wheel 
  * the fixed number of turns in the coil 
  * the fixed speed at which the magnetic flux changes by the rotating tone wheel. 
  
-The number of turns of wire is set at the factory and the speed of the tonewheel is set by the SynchronousMotor. Only the distance between the magnet and the tonewheel can be adjusted by a technician, ToneWheelGeneratorOutputLevels. The closer the magnet is moved towards the tonewheel, the greater the output voltage (although this does affect the tone quality as well). While the organ is being played, these things never change so the output voltage from each coil is constant. 
+The number of turns of wire is set at the factory and the speed of the tonewheel is set by the SynchronousMotor. Only the distance between the magnet and the tonewheel can be adjusted by a technician, ToneWheelGeneratorOutputLevels. The closer the magnet is moved towards the tonewheel, the greater the output voltage (although this does affect the tone quality as well). While the organ is being played, these things never change so the output voltage from each coil is constant. While the voltage is fixed, the output current is inversely proportional to the total resistance of the parallel keying circuits. So when the resistance drops by half when two key contacts are closed, the output current doubles. This doubling of current is evenly split between the two key contacts so, as Hammond noted, "...the current flow through each of the different circuits will be substantially the same..." Note that this relationship is linear
  
-While the voltage is fixed, the output current is inversely proportional to the total resistance of the parallel keying circuits. So when the resistance drops by half when two key contacts are closed , the output current doubles . This doubling of current is evenly split between the two key contacts so, as Hammond noted, ". ..the current flow through each of the different circuits wil be substantially the same ..." Note that this relationship is linear. 
+But the ear is not a linear device! When the Model A output coils were adjusted to provide the same output voltage at each coil , the organ was considered too ''bright'' . This is because the ear responds better to higher frequencies than to lower frequencies. Hammond began correcting this problem by adjusting the distance between each magnet and the tonewheel so that lower frequencies have a higher output voltage than higher frequency generators . As a result, early Model B organs have a very pronounced bass . In later console organs, Hammond replace the fixed 15 ohm wires with different values of resistance wire between the tone generators and the key contacts to ''taper'' or ''voice'' the organ . As additional key contacts are closed, the resulting increase in output current is non- linear. 
  
-But the ear is not a linear device! When the Model A output coils were adjusted to provide the same output voltage at each coil, the organ was considered too ''bright''. This is because the ear responds better to higher frequencies than to lower frequencies. Hammond began correcting this problem by adjusting the distance between each magnet and the tonewheel so that lower frequencies have a higher output voltage than higher frequency generators. As a result, early Model B organs have a very pronounced bass. In later organs, Hammond added different values of resistance wire between the tone generators and the key contacts to ''taper'' or ''voice'' the organ. As additional key contacts are closed, the resulting increase in output current is non-linear. Resistance wire values range from 10 to 100 ohms and depend on the frequency of the generator and the harmonic to be used. In effect, Loudness Robbing was intentionally created to ''compress'' the range of loudness between settings with few and lots of harmonics. This allowed the organ to have a consistent volume as more harmonics are added. 
+Hammond used resistance wires with values ranging from 10 to 100 ohms and connected these wires based on the frequency of the generator and the harmonic to be used. The resistor ''wire-harness'' is a carefully constructed bundle of pre-cut wires tied together in a specific order and arranged to connect from the generators to each key contact. In effect, Loudness Robbing was intentionally created to ''compress'' the range of loudness between settings with few and lots of harmonics. This allowed the organ to have a consistent volume as more harmonics are added. 
  
-Resistance tapering is not provided in the Model M and other spinet organs since the extra effort to taper the manuals added to the production cost. In the spinet organs, the resistance is fixed at 16 ohms. As upper harmonics are added by the drawbars, the player must adjust the volume pedal to keep the preceived loudness the same. This is one reason why ''classic'' B3 drawbar settings sound different on the spinet organs. 
+Resistance tapering is not provided in the Model M and other spinet organs since the extra effort to taper the manuals added to the production cost. In the spinet organs, the resistance is fixed at 16 ohms. As upper harmonics are added by the drawbars, the player must adjust the volume pedal to keep the preceived loudness the same. This is one reason why ''classic'' B3 drawbar settings sound different on the spinet organs. For those thinking of tapering their M3, beware! It would be a huge undertaking to add a console organ-like wire harness. It ''may'' be possible to insert individual resistors or trim pots between the wires and the key contacts but even this would be a lot of work

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