Pythagoras found out working with a monochord (a one string instrument) that a string is oscillating not only as a whole one but in integer parts of itself (> physics).
The half string has the double frequency as the original, the third string the triple frequency and so on.
That fascinating interdependence of length and frequency Pythagoras called “harmonical” because of the integer relationship.

Jean Baptiste Joseph Fourier developed equations which helped the warlords to construct cannons who didn’t burst because of the thermic tensions.

Georg Simon Ohm transferred this equations to sound phenomena. This is not as well-known as the fact of his electricity laws

Hermann Helmholtz finally had with his „Resonatoren“ in the 19. century the first synthesizer:
The hollow metal forms (see left) had different sizes. Helmholtz stimulated a big one and held a litlle one to his ear. If the little resonator was oscillating (resonating), it had a frequency of an overtone of the priming resonator, it possessed a partial frequency of the basic one.
Later on Helmholtz refined his system by using electical driven tuning forks.

Thaddeus Cahill constructed in 1896 his “Telharmonium” to be the first electrical driven synthesizer on base of Additive Synthesis.
The keyboard had to take a train to move because of his 200 tons. Since 1907 the sounds could be rented, had to be sent via telephone wire and disturbed the speech enormously!

Mr. Hammond with his organ finally took care that electrical driven sound generators had a tremendous triumph.
Anyway, there is a lot of work to do to get the sounds more lively.