The Lev Antenna Revisited

FredM Said: From here (http://www.thereminworld.com/forum.asp?cmd=p&T=5049&F=1&p=2)

[i]my advice to anyone who discovers something 'strange' is to present what they have discovered WITHOUT trying to explain the mechanism - unless they are sure their hypothesis is rational and does not contradict the fundamental laws.. It MAY be that some physical fundamental will need to be re-evaluated.. But this is extremely unlikely - and if one presents a hypothesis which goes against these laws, no-one will bother examining the phenomena.[/i]

I agree with you Fred, that what I observed probably fell on deaf ears because my explanation of the phenomenon is most likely inaccurate. After seven years I have received very little theoretical feedback though all of my theremin designs have been linear.

Using a tight coil antenna gives a perfectly linear pitch field “relative” to the note intervals or spacing found on a piano keyboard, from the outside right up next to the antenna. This is what makes the coil antenna approach so interesting.

Today operating my pitch oscillator at 900 kHz instead of 850 kHz and using tubes/valves instead of transistors allows me to bypass using any sort of inline LC antenna tuning. The tuning is by the slight stretching of the spring antenna coil. This does not seem to be critical when using the spring of choice found at every hardware store here in the states. The tuning of the antenna is very stable indoors or out once it is initially set.

Understanding the phenomenon is not as important as it is to experience something so unusual over a standard theremin pitch field. The [b]Theremax[/b] operates around 820 kHz and might be a good theremin to try the Lev Antenna on. I would move the operating frequency higher in case freq is an important aspect relative to the dimensions of the antenna spring coil design.

One day most theremins will be linear, not almost linear, once someone explores this and makes a validating statement about the Lev Antenna (http://www.oldtemecula.com/theremin/index.htm).

Perfect linearity will not make anyone a perfect Thereminist but it does give you a significant advantage.

Christopher
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Perfect linearity (the same distance between semitones throughout the entire range of the theremin) will not improve the level of theremin playing one single bit. Why? Because imperfect linearity is not what makes the theremin the most difficult musical instrument to play that has ever been conceived.

Coalport said:

[i]Why? Because imperfect linearity is not what makes the theremin the most difficult musical instrument to play that has ever been conceived.[/i]

Don’t be silly, the theremin is the most difficult instrument to play well!

You and I are getting older; in the states we call ourselves the boomer generation. It is important that we pass down the knowledge we have accumulated to the younger generation. There are discoveries about the theremin that are yet to be found.
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Coalport wrote:

"imperfect linearity is not what makes the theremin the most difficult musical instrument to play that has ever been conceived."

What does?

Violinist Itzhak Perlman once said in an interview that the difficulty of any musical instrument can be judged by how long it takes a newcomer to learn to play a simple melody accurately and consistently. When I said that the theremin is the most difficult instrument to play that has ever been conceived, I should have mentioned the above definition of "difficulty".

I have often heard people say, "The theremin is the most difficult instrument to play well", but I'm never sure what that means because the word "well" is so subjective. A couple of weeks ago someone told me that, by far, the greatest thereminist who has ever lived is Jimmy Page.

What makes the theremin so difficult to play with precision is not the fact that the linearity is uneven. It is that the interface is invisible. The linearity of guitars, violins and cellos is also uneven (it stretches toward the bass and squeezes toward the treble) but it is fairly simple to adapt to because it can be seen. It's easier to see on a guitar than on a violin, but in both cases there is a physical string and fingerboard that can be divided by sight and touch.

With the theremin, there is nothing to see and nothing to touch. If I ask you to play an octave interval on a theremin with speed and accuracy, your ability to do this will not be influenced by whether or not the spacing between the twelve intervening semitones is even. It's all hand/ear coordination, muscle memory, and familiarity with the particular instrument you're playing.

Clara Rockmore once said that one of the reasons she did not teach was that reliable, professional level theremins (RCA's) were no longer available. She went on to say that in order for lessons to be effective a student would have to take them on the instrument that he or she was playing on a daily basis. Clara felt it would not make sense for a student to play her theremin for lessons, and then go home and play some other instrument with an entirely different linearity.

Piano teachers have two pianos in their studios - one for the student and one for the teacher - and pianos, although they may vary in size, tone, etc., all have the standard concert keyboard with key sizes that were universally agreed upon long ago. The piano your kid takes lessons on is pretty much the same as the one at home in your living room.

Here's where a standard concert linearity for theremins (if such a thing were possible) would come in handy. It would not make the instrument easier to play, but it would mean that a thereminist could play any theremin, any time, any where, without having to adapt his or her technique.

The "ruban" (aka slider) of an ondes martenot, the heterodyne sister of the theremin, has the standard concert spacing of a piano, but here's the interesting thing: if the theremin had the same spacing, the playing arc in order to have the same range would have to be several feet wide. This would be impossible for thereminists. If we were all to agree on an appropriate distance between semitones in the theremin playing arc, what would it be?

Remember, you have to squeeze all the notes you will want (three and a half or four octaves) into the space of an arm's length. If your playing arc is about 18 inches, that will give you roughly five sixteenths of an inch per semitone over four octaves.

If guitars had even spacing over the entire fingerboard, and if the spacing corresponded to the one and a quarter inch standard spacing between the frets on the lower notes (first and second frets), then guitars would have to be ten inches longer than they now are......hmmmm

Coalport said:

[i]If we were all to agree on an appropriate distance between semitones in the theremin playing arc, what would it be?[/i]

The opening thread is placed under the Construction Forum and does not attempt to give any recommendations about playing but I will answer this question.

The Lev Antenna linear pitch field is “linear” regardless of what interval widths or semitone spacing is selected. There would be no standard width as this is determined by the size of your hand or personal preference. The pitch knob sets this spacing just as it does for a non-linear pitch field.

Your input above is excellent, who is Jimmy Page?

Hello Ruslan,

Yes that webpage with my links could use a makeover.

The coiled antenna approach has worked on my transistor designs and tube/valve designs operating around 900 kHz. The three different theremin models I verified this with used Hartley Oscillators.

What does the antenna look like?

It is just a spring coil of a specific size. Using a spring requires a little more thought to construction. I sprayed my latest spring with a non-condutive gold paint with no problems.

One picture connected to my experimental tube/valve setup is at the bottom of this page. (http://www.oldtemecula.com/theremin/tube_valve.htm)

The spring can be held in or on a pvc pipe. I prefer an exposed mounting so the response is not affected by any dielectric influences. I did not notice any negative effect with the spring inside a pvc pipe.

I don't know of anyone else using this approach..

RS asked: ....who is Jimmy Page?

LOL....When I asked the person who told me he thought Jimmy Page was the greatest thereminist who ever lived how he felt about the theremin playing of Clara Rockmore, he asked: "Who is Clara Rockmore?"

I am beginning to wonder if it is wise to support a system that upholds the rights of idiots to hold idiotic and uninformed opinions. If they take over the bridge, the ship is going down!

[i]"If they take over the bridge, the ship is going down!" - Coalport [/i]

LOL! ;-)

Bad news.. The ship IS going down!

Fred.

I WISH TO MAKE IT KNOWN PUBLICLY THAT I DO NOT BELIEVE ANY OF THE CLAIMS REGARDING THE LEV ANTENNA.

HAVING EXAMINED THE ANTENNA, BOTH PRACTICALLY AND THEORETICALLY, I DO NOT BELIEVE THESE CLAIMS CAN BE SUBSTANTIATED.

I BELIEVE THE  REASON FOR THE EXCEPTIONAL LINEARITY OF LEV THEREMINS HAS PROBABLy BEEN DISCOVERED - AND THAT IT IS DUE TO LEV's OSCILLATOR DESIGN WHICH HAS BEEN MISUNDERSTOOD AND WRONGLY COPIED FOR DECADES!

Christopher,

I am interested to know how you define "perfect" linearity.

I personally do not believe perfect linearity can be obtained - only good linearity. In my view, linearity is good if it is better than 20% total error per octave over a 5 octave range.. as in, the lowest octave is no more than 20% greater in length than the highest octave under all normal conditions.. But perhaps I have defined this based on what I have been able to achieve... Wherever one defines it, Perfect is not available - The only way to get really good linearity (say 1%/Octave) under ALL conditions would be to have an intellegent antenna which could focus on the players hand and exclude any variation in background capacitances.

Every time a player changes their body position, or positioning of the theremin in relation to walls / cables / amplifier etc, the linearity of the playing field will alter - re-tuning the null point to bring it to the same position reletive to the antenna will not correct changes to the linearity which must be caused whenever the environment changes - and this would be true regardless of what mechanism operates, be this capacitive (as I believe) or some other "loading" mechanism.

I have played with antennas having inductors wound on them (I read your article and followed what I percieved to be the essentials, winding insulated multistrand hookup wire of 1.2mm copper wire over a 15mm bakalite rod, with 16 turns per inch) and never found any change in linearity - but, in fairness, I did not use a spring and did not follow your instructions to the letter..

I measured an inductance of about 29uH on the antenna winding - this is a tiny inductance compared to the EQ coil.

I believe what you say, but my attempt to simply replicate your results failed.. I used an oscillator similar to the SC theremin, and have since found problems when operating these oscillators with equalizing inductors so I may repeat the experiment if I get back to my lab one day..

I have some vague hypotheses as to how a shaped antenna (as in, think about your Lev antenna as a spiral capacitive sensor rather than as an inductive antenna) could affect linearity - but the maths is way beyond me.. I have found that long thin antennas have better linearity at the bass end, and that fatter shorter antennas have better linearity in the mid field, but awful linearity when one gets close to the antenna - And I can see rational explanations for these phenomena (its all about geometry and the effects of angular capacitive coupling to the players hand, arm and body) - So PERHAPS a spiral antenna of the right dimensions could improve linearity.

I am reasonably sure that whatever mechanism is involved, the 30uH inductive component @ 900kHz is not going to be the reason for any improvement in linearity.. A spiral has some interesting properties.. and there are some extremely interesting issues when it comes to effective capacitive 'plate' area.. There will probably be a higher electron (electrostatic) concentration between the windings on the antenna - and I am sure the antennas total capacitance will be greater than one would get if the conductive area of the wire/spring was compressed into a single composite rod.. This inter-winding capacitive 'field' would have a different relationship to the 'ground plate' than the actual conductors would have.

Alas, whilst not 'pseudo science', the physics of electrostatics is not well understood and is even less well documented, and even that which is "easy" becomes horrendously complicated when one tries to analyse the operation of even a few capacitive plates - Try, for example, to do the maths on two plates at right angle to each other, then extend this by making the distance variable, then by making the angle variable.. if you get past the first step you are doing better than I did, or have a lot more patience! ;-)

I would put my money on it all coming down to