The Theremin Pitch Field, The Mystery Deepens . . .

Gordon,

this is excellent!

GordonC>> You have a real knack for explaining things clearly. Your "jug of water" illustration resulted in a light-bulb moment for me ... which is pretty good seeing as I certainly fall into the non-electrician category!

Cool.

As the title of the thread asserts, the pitch field (and the volume field - equally important!) are mysterious. If you watch people trying the theremin for the first time, they are mystified - they are trying to interact with something that they cannot see or feel, that requires a coordination they are unfamiliar with, and that they do not understand.

I figure; the better the understanding, the better the interaction. That, and familiarity. (*) So I've been thinking about this on and off for three and a quarter years.

(*) To provide an opposing point of view, I taught my wife to cycle. First I explained the physics involved in centrifuges, and why bicycles tend to stay upright. Then I pushed her down a steep hill and let go. The second step probably helped more than the first.

The physics (and electronic theory) can get more involved as the shape of the antenna changes and as we consider a more complex impedance as the load.

Passive electronic filters (ones that only use Rs, Cs and Ls) can be get pretty complicated, since the reactive part can vary for different frequencies. I am guessing that an accurate model (i.e. the miserable mess of equations) would look more like a complicated RLC filter network than just a simple capacitor.

We could get an intuitive feel for this by altering our impedance ... Gordon's egg beater is a great example of this! A time-varying, electronic load. Very clever effect, by the way!!

It gets even messier taking all the reflections off of nearby walls and objects into account. Not only do you have a nearby load, but you have electric field waves coming back in and out of phase to collide with that being radiated. That's what makes the Lev antenna even more interesting ... in one sense, you are adding parallel capacitance across windings of a coil (the spring). In another, the spring radiates in both the vertical and horizontal direction, adding other possibilities (reflections off the ceiling maybe?).

I really hated all this transmission line stuff in college and it just insists on coming back to bite me! LOL


Don

Reflexions may alter the amplitude by superposition. This should not be a matter in a serious heterodyning design, since it is the frequency and not the amplitude which makes the music.

@Don. :-) The Frothatrill. A hand-held milk frother, illustrated here by Dan:

link (http://www.youtube.com/watch?v=w3h9O9LGmNo#t=3m05s)

Mine differs from Dan's in that I attached a fuse-wire propellor to the end rather than bending the stem, and I hold it pointing towards the audience, as one might sweep an electric torch at waist height, rather than pointing it towards the pitch rod.

Incidentally, I just put a G-Clamp on my etherwave, close to the where the loop meets the body on the audience side, as an electromechanical articulation regulator. (Adapted from an idea posted on Levnet by LPK recently.)

That was a very interesting and informative post, Gordon! More food for thought about interesting things to try.

Don