Help! Some questions on modifying Moog Etherwave Theremin

Hello

My name is Birna and I just assambled my first Moog Etherwave theremin kit! I’m an artist and have been captured by the magic of theremins for a while and am planning to use the function of a theremin in a sculptural setting.

So I decided to start with assembling the Etherwave kit to get a better feeling for the instrument and how it works but the thing is that I actually want my theremin to behave a bit differently than the regular instrument should. I basically want to make a sculptural landscape where some of the sculptures have theremins embedded so as other sculptures move or viewers walk through the landscape, a soundpiece is forming.

Since I’m so new to the theremin I’m hoping I can ask for some advice from the Theremin World expertise! Here are the questions I’m wondering about at the moment:

Preferably I’d want the physical range of the antennas to be around 2-3 meters and I’m wondering how (and if) I can modify the etherwave to such a range? 

I’m trying to get there simply by adjusting the range knob (didn’t get there yet) but I’ve seen in some threads a suggestion that a longer antenna will do it - is that the case?

 Another two questions about the antennas: If I’ve found a good length for a home made antenna, does the shape of it make a difference to the sound? I read somewhere that it shouldn’t change too much and that the shape of the classic volume antenna was mostly a historical design rather than a function..

 Secondly, since it’s gonna be more a sculpture and less an instrument I was thinking of making the antennas stand independently from the casing around the circuit board. So the casing is enclosed and situated on the floor with the two wires connecting the antennas sticking out and leading to the antennas which will be freestanding on specially made stands. It feels to me like that should work fine, but maybe someone knows better?

My last question is considering the casing I’d like to cast my own case for the theremin out of plastic and I was wondering if anyone has used plastic for casing and if there are some things to keep in mind?

As you can see I’m really new to this electronic world but nevertheless excited! I’m to throw all these questions in here but any pointers would be appreciated.

-Birna

"I basically want to make a sculptural landscape where some of the sculptures have theremins embedded so as other sculptures move or viewers walk through the landscape, a soundpiece is forming."  - Birna

Theremins transmit / receive RF to some degree, and can definitely interact via their AC capacitance fields (same thing?).  So in order to have multiple conventional Theremins situated near each other they may need to be detuned from one-another.  The amount of detuning depends on how close they are, and the range they need to work over (the nearest your hand / body will be to the antennas).  Detuning can be as simple as making one antenna larger than another, padding the antenna with a few pF, or adding some series inductance.  This is something you have to experiment with to get right.

"Preferably I’d want the physical range of the antennas to be around 2-3 meters and I’m wondering how (and if) I can modify the etherwave to such a range?"

If you read papers on capacitance you'll see that it scales with geometry.  Specifically, the capacitance is proportional to plate area divided by the distance between the plates.  So if you want more distance you increase the antenna area, and have it interact with your body rather than your hand.  The Etherwave may need modification to the inductors / capacitors in order to work with a larger plate antenna (I have no direct experience doing this modification to the EW).

"I’m trying to get there simply by adjusting the range knob (didn’t get there yet) but I’ve seen in some threads a suggestion that a longer antenna will do it - is that the case?"

You want more area, like a square or circular plate, or something roughly like that.  A 3D shape like a ball should work too.  And you will almost certainly need to adjust the internal variable inductors (which can be a bear).

"Another two questions about the antennas: If I’ve found a good length for a home made antenna, does the shape of it make a difference to the sound? I read somewhere that it shouldn’t change too much and that the shape of the classic volume antenna was mostly a historical design rather than a function.."

If you are playing it musically you want a long thin antenna, because this helps linearize the near field pitch.  The shape of the antenna can only influence the sound (timbre) via minor second order means.

"Secondly, since it’s gonna be more a sculpture and less an instrument I was thinking of making the antennas stand independently from the casing around the circuit board. So the casing is enclosed and situated on the floor with the two wires connecting the antennas sticking out and leading to the antennas which will be freestanding on specially made stands. It feels to me like that should work fine, but maybe someone knows better?"

The floor will definitely influence the tuning and sensitivity, it's like having a really big person standing very close to the Theremin.  I'd place it above the floor, as high as reasonably possible.

"My last question is considering the casing I’d like to cast my own case for the theremin out of plastic and I was wondering if anyone has used plastic for casing and if there are some things to keep in mind?"

Plastic would be a better choice than the standard wood case.  The wood case is not transparent to capacitance, so it alters the tuning when you remove and replace the cover (an annoying thing when you're trying to get the tuning right).

Wow thanks Dewster for a great reply!!

I'm currently busy with adjusting the internal inductors and true, it is quite tricky but also fun to experiment with!

Ahaa now I'm understanding it a bit better with the relation between the antennae area and distance.. I'm gonna try it out on the Etherwave and see where I get without any inductor modification. 

Thanks a lot for all the advice - I guess I just have a lot of experimenting to do for now.