7. General Theory

The electronic organ, AN/TNP-1, makes use of two simple principles.

a. PURE SOUND. Pure sound results from the vibration of any body. It can be classified by the ear when its vibration rate is nearly constant.

b. COMBINED SOUNDS. Pure sound is dull and uninteresting. It pleases the ear only when combined with other sounds called harmonics, which are whole number (1,2, 3,4, etc.) multiples of its rate of vibration. When the relative loudness of harmonics is altered, the basic sound retains its identity but has a different effect on the listener.

8. Application of Theory

In the electronic organ, AN/TNP-1, the principles of sound referred to in paragraph 7 are applied as follows:

a. TONE GENERATION. The drive shaft and gear assembly rotates a number of tone wheels. Wheels of different construction are provided for each identifiable sound used by the organ. Each wheel operates in a magnetic field to generate continuous electrical pulses at a rate characterized by the construction and speed of the wheel. Individual tone wheel pulses are amplified and converted to sound only when organ keys or pedals are operated to complete circuits through the instrument. Each key can complete circuits for as many as nine tone wheels. These nine wheels represent nine sounds that are identifiable with a particular key on the manual.

b. TONE COMBINATION. The relative strength of the nine tones connected through each key is controllable by the preset keys. Each preset key has separate passages for the nine tones transmitted to it from any operated playing key. From the preset key each of the nine tones is transmitted to one of nine predetermined connecting points on a transformer. This transformer is designed to deliver sounds of different volumes from each connecting point. Each preset key is connected differently through the transformer to provide an individual volume combination for the nine tones channeled through that key. Thus, by choice of preset key a choice of different harmonic relationships is possible, resulting in variety in the quality of tones.