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If you really want to know about the technology of the Hammond organ, the best place to get a true understanding about how the organ works is to read the patents. Here is a somewhat exhausting list of Hammond patents related to musical instruments (and a couple oddball Laurens Hammond patents not related to musical instruments...). You'll find a lot of information in the patents about concepts like LoudnessRobbing, KeyClick, etc. that really explains what is going on. There are also some patents listed here that were never used on any tonewheel Hammond organ. Here are a few of the patents issued to LaurensHammond and Hammond Organ Company engineers JohnHanert, Gilbert Smiley, W J Wehermann, Herbert Meinema, George Stephens and Thomas George:

Year     Number        Inventor(s)                         Title/Description
1921   1,435,520   Hammond           Stereoscopic Motion Picture (3d movies!).
1929   1,719,805   Hammond           Alternating Current Clock (synchronous motor driven).
1934   1,956,350   Hammond           Electrical Musical Instrument (original organ patent).
1936   2,036,892***Smiley            Art of Producing Musical Sounds Electronically (RE20825).
1936   2,083,246***Smiley            Electronic Musical Instrument (RE20831).
1937   2,099,204   Hammond           Multiple Key Switch (keyboard switch contacts).
1938   2,117,002*  Hammond           Keyboard for Musical Instruments (keyboard construction).
1938   2,126,464***Hammond           Electrical Musical Instrument (Touch sensitive circuit).
1938   2,126,682***Hammond           Electrical Musical Instrument (Tube frequency divider).
1939   2,159,505   Hammond           Electric Organ (chorus generator).
1939   2,161,706   Hammond           Electrical Musical Instrument (Delay circuit).
1939   2,173,888   Smiley            Electronic Musical Instrument (Grid-bias keying).
1939   2,184,424   Hammond           Electrical Musical Instrument (Keyboard construction).
1940   2,199,702   Hammond           Method of Broadcasting (Radio studio organ miking).
1940   2,203,432   George, Hammond   Electrical Musical Instrument (6 oscillators).
1940   2,203,569   Hammond           Musical Instrument (Solovox).
1940   2,216,513   Hammond           Electrical Musical Instrument (Slow decay with capacitors).
1940   2,211,205   Hammond           Reverberation Apparatus (Shipping lock for 2,230,836).
1940   2,214,764   Hammond           Electrical Musical Instrument (Electrostatic tone generator).
1940   2,221,188   Hammond           Electrical Musical Instrument (Swell and tremulant circuit).
1940   2,224,729   Hammond           Electrical Musical Instrument (Improved grid-bias keying).
1941   2,230,836   Hammond           Electrical Musical Instrument (Original reverb patent).
1941   2,233,258   Hammond, Hanert   Electrical Musical Instrument (Solovox keyboard).
1941   2,241,363   Hammond           Electrical Musical Instrument (Auto pedal note).
1941   2,245,337   Hammond           Electrical Musical Instrument (Tube top octave generator).
1941   2,245,338   Hammond           Musical Instrument (The amazing Novachord!).
1941   2,251,051   Hammond           Electrical Musical Instrument (Tone control).
1941   2,251,052   Hammond           Electrical Musical Instrument (Vibrating reed vibrato).
1941   2,253,782   Hammond, Stephens Keyboard for Electrical Musical Instruments (Solovox).
1941   2,254,284   Hanert            Electrical Musical Instrument (Single octave keyboard).
1941   2,254,366   Hammond           Variable Impedance (Swell pedal system).
1941   2,260,412*  Stephens          Key Action for Musical Instruments (keycomb, etc.).
1941   2,262,179   Hammond           Musical Instrument (Novachord case).
1941   2,262,494   Hammond           Electrical Musical Instrument (Touch sensitive circuit).
1941   2,266,030   Hammond           Electrical Musical Instrument (Envelope control).
1942   2,274,199   Hammond           Electrical Musical Instrument (4-Channel organ system).
1942   2,276,389   Hammond           Electrical Musical Instrument (Octave dividers).
1942   2,281,495   Hammond           Frequency Generator (Electrostatic tone generation).
1942   2,301,869   Hammond           Frequency Generating System (Tub oscillators).
1942   2,301,871   Hanert            Electrical Musical Instrument (Double touch keyboard).
1943   2,310,429   Hanert            Electrical Musical Instrument (Multichannel organ).
1943   2,314,496   Hammond           Electrical Musical Instrument (Unusual tonewheel generator).
1943   2,323,392   Hammond, George   Electrical Musical Instrument (Vibrato circuit).
1943   2,332,076   Hammond, Hanert   Electrical musical instrument (Improved 4-channel organ).
1944   2,342,338   Hanert            Electrical musical instrument (Percussion sound generator).
1944   2,357,191   Hanert            Electrical Musical Instrument (Single octave pedal clavier).
1945   2,373,560   Hanert            Sound Recording Method and Apparatus (Recording with vibrato).
1945   2,382,413*  Hanert            Electrical Musical Apparatus  (Scanner vibrato).
1947   2,429,226   Hanert            Electrical Musical Instrument (Keying system).
1947   2,432,151   Hammond           Amplifying System (Amplifier with auto gain control).
1949   2,480,131   Hammond           Electrical Musical Instrument (Pedal clavier with coil-spring pickups).
1949   2,480,132*  Hammond, Hanert   Electrical Musical Instrument (Single octave pedal clavier).
1950   2,498,367   Hammond, Hanert   Electrical Musical Instrument (Chorus generator).
1950   2,499,244*  Hammond, Stephens Pedal Clavier for Musical Instruments (Spinet pedal clavier).
1950   2,500,820   Hanert            Electrical Musical Instrument (Tube generators w/chorus effect).
1950   2,500,821   Hanert, Hammond   Electrical Musical Instrument (Pedal generators w/slow decay).
1950   2,501,172   Hammond, Hanert   Electrical Musical Instrument (Bass tone generator).
1950   2,506,451*  Hammond           Organ Console (M series spinet console design).
1950   2,508,514   Hanert, Hammond   Electrical Musical Instrument (Complex first octave tonewheels).
1950   2,509,923*  Hanert            Electrical Musical Apparatus (Scanner vibrato improvements).
1951   2,560,568*  Hammond, Hannert  Vibrato Apparatus (Variable capacitor scanner).
1951   2,565,512*  Meinema           Tone Control Apparatus (Improved drawbars).
1951   2,577,752   Hanert            Tone Quality Control Circuit for Electrical Musical Instruments.
1951   2,577,753*  Hanert, Hammond   E.M.I. with Tone Sustaining Means (M series pedal sustain).
1952   2,580,424   Hanert            Vibrato Apparatus for Elec. Musical Inst. (Tube vibrato).
1952   2,583,566*  Hanert            Elec. Musical Inst. (Manual selective vibrato, 3 series).
1953   2,626,325** Hammond, Stephens Pedal clavier switch mechanism.
1953   2,645,968   Hanert            Electrical Musical Instrument (Tube organ).
1953   2,646,468*  Hanert            Ear response compensated volume control apparatus.
1954   2,681,585   Hanert            Elec. Musical Inst. Producing Chorus Effects (Tube chorus).
1954   2,691,318   Hanert            Electrical Musical Instrument (Seven oscillator organ).
1957   2,790,906   Hammond           Electronic oscillator (Adjacent notes share oscillator).
1958   2,828,659   Hanert            Electrical musical instruments {Percussion circuit).
1958   2,835,876   Hammond           Adjustable inductance (Adjustable inductors for tuning).
1958   2,845,831   Hammond           Keyboard & Switching for E.M.I. (Chord organ buttons).
1958   2,846,913   Hammond           Circular scale electrical musical instrument.
1959   2,878,708   Hanert            Capacitive switching apparatus (Manual keying).
1960   2,905,040   Hanert            Method and Apparatus for Producing Chorus Effects in Music.
1960   2,922,329   Hanert            Elec. Musical Inst. with Multiple Utilization of Tone Sources.
1966   2,933,004   Wehrmann          Combined Piano and Electrical Monophonic Instrument.
1960   2,942,070   Hammond, et. al.  Means for Binaural Hearing (pseudo-stereo).
1960   2,943,527   Hanert            Adjustable Tune Producing Instrumentality.
1960   2,949,805   Hammond           Artificial Reverberation Control Apparatus.
1960   2,951,412** Hanert            Electrical Musical Instrument with Percussion Apparatus.
1960   2,953,055** Hanert            Percussion Tone Electrical Musical Instrument.
1960   2,953,056   Hanert            Percussion Tone Electrical Musical Instrument.
1961   2,967,447** Hanert            Apparatus for Translating Electrical Musical Tone Signals into Sound (Reverb).
1961   2,972,273   Hanert            Polyphonic Percussion Control Apparatus.
1961   2,982,819** Meinema et. al.   Artificial Reverberation Apparatus ("Necklace" Reverb).
1962   3,037,414** Meinema           Artificial Revereration Control Apparatus.
1962   3,048,072   Hanert            Apparatus for Producing Psuedo-Stereophonic Effects.
1962   3,051,032   Hanert            Single Manual Double Countermelody Electrical Musical Instrument.
1962   3,070,659   Hanert            Artificial Reverberation Control Apparatus.
1963   3,077,136   Hammond           Capacity Tuned Oscillator
1962   3,109,878   Hanert            Percussion Tone Monophonic Electrical Musical Instrument.
1966   3,260,784   Wehrmann          Electronic Musical Instrument Having One or More Keyboards.

There are also a number of Design Patents:
1950   158,625     Stephens         Electrical Musical Instrument (M series spinet, offset manuals, 1 octave pedals).
1961   190,140     Palma            Electric Organ (A-122 Contemporary console design).
1962   192,450     Miller           Electric Organ (A-102 French Provencial console design).
1962   192,882     Miller           Electric Organ (A-101 Traditional console design).

*   These patent numbers are found on the nameplate of M3 organs dating around 1953-1954.
**  In addition to the patent numbers on the M3, these patent numbers are found on the nameplate of M100 organs.
*** In addition to 2,117,002, these patent numbers are found on Novachord nameplates

To retrieve these patents, copy the patent number and search the US Patent Office:

You'll need a free tiff viewer add-in to view the images in your brower: or

In all, Laurens Hammond had 91 patents issued to him during his career. The non-organ related patents were for things like 3d movies, electric clocks and aircraft controls.

See also DonLesliesPatents and CahillPatents

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