AETHERPHON, global theremin family

Quoting David Vanhorn <dvanhorn@...>:

>
>
>   >I think it would be very interesting to see a 3D plot of the capacitance
>   >field of the theremin, with those tuning setting superimposed on it.
>
> That would be a big project.  Lots of data points to collect, and 
> rather difficult.
>
> The first thing, is to discard the idea that the "antennas" are 
> acting as antennas.  They are capacitor plates. At these low 
> frequencies they aren't anywhere near long enough, and the fact that 
> diameter is as important as length confirms this.

We tend to think that a given distance between one's hand and the pitch 
antenna
is produces a given pitch (let's call this the x-axis).  However, the hand's
up-down position (the y-axis) also effects the pitch.

Playability increases when the antenna's sensitivity along the y-axis is
minimal.  In fact, this issue may be more fundamental to playability than
linearity.  That is, if a Theremin has great linearity but is overly sensitive
on the y-axis, then it is still difficult hit notes precisely.

When I replaced my stock Tmax antenna with a longer and thicker antenna (a
chrome plated pipe), the playability increased because the sensitivity along
the y-axis decreased.  The linearity might have been improved a little, 
but the
big advantage was to have less sensitivity to up-down motion.

Has anyone looked in to the up-down (y-axis) sensitivity issue?

That is, if a Theremin has great linearity but is overly sensitive
   >on the y-axis, then it is still difficult hit notes precisely.
   
Makes sense to me.  The volume could well be done by a flat plate, you don't really need any resolution.  Long skinny antennas have a problem in that they get droopy, and would tend to add problems.  For a given material, there will come a range of workable lengths.

Another thing about long antennas, as you approach, your hand is close to some of the antenna, but far from other parts.  Think of it this way.. Slice the antenna into 1 inch segments, and ar 3' distance measure the distance to your hand.  Not much difference, so the capacitance change per inch of motion is calculated by the effective area of the antenna and hand, distance, and not much else.

Now try again, 6 inches from the antenna. For a few inches length, you get the same distance, but other parts are farther away, and therefore the change in capacitance is smaller per inch than it would be if we used flat plates.  So this has a linearizing effect.

Also, there is a big difference in where the antenna coils are tuned to, but that's another hard one to express.