theremin virgin!

Posted: 3/4/2006 8:42:23 PM

From: Croxley Green, Hertfordshire, UK

Joined: 10/5/2005

Hi Hels,

It's radio waves.

Do you have some way at school of creating two continuous notes in the audible range, both the same frequency, and varying the pitch of one very slightly? Doing so will cause a throbbing sound called a beat frequency, created from the two sound waves interfering with each other.

If the two original notes were high enough frequency they would be inaudible, and the beat frequency would be fast enough to be a continuous note, which could be varied by varying the frequency of one of the high pitched notes.

A theremin creates two frequencies in the radio signal range, far too high to hear. Once of the signal generators is connected to the pitch antenna, and can be made to vary in frequency by coming close to it, in the same way that moving near a television or radio aerial can cause it to go out of tune (body capacitance.) The two signals are added together electronically (this is called heterodyning) to produce the beat frequency signal that you can hear.

The volume antenna is connected to a different part of the circuit to affect the volume rather than the frequency, but works by body capacitance just the same.


PS Writing poetry to music was something I did at primary school. It was Holst's Planet Suite, but we were not told that until afterwards. (I wrote a poem called The Sea that won me a ten pound book token in a competition run by the Daily Mail that our teacher entered all the poems in.)
Posted: 3/4/2006 9:09:07 PM

From: Kansas City, Mo.

Joined: 8/23/2005


To elaborate on Gordon's post:

The two high-frequency signals are not really added -- would be more accurate to say that they are "combined" such that the difference between the two frequencies is detected (heterodyned).

(as a sidenote, the SUM of the two frequencies is also generated, however is filtered out. The Theremin only works with the difference frequency.)

The fundamental force at work in all electronic ciruits (and certainly in the Theremin) is the electromagnetic force.

The question, "Is it electricity or magnetism" could lead you into a discussion of the electromagnetic force and the discoveries of Maxwell.
Posted: 3/5/2006 4:05:37 AM
Charlie D

From: England

Joined: 2/28/2005

The theremin does employ the principals of electromagnetic induction to generate the huge fields that surround both antennae.

Something that always makes young children recoil in horror if you tell them it whilst they're 'playing' the instrument is that they are conducting electricity if they stand near to the instrument. It is that conductivity that explains why leeks too can play the theremin, but plastic poles cannot.
Posted: 3/5/2006 4:39:30 AM

From: Croxley Green, Hertfordshire, UK

Joined: 10/5/2005

Thank you for your correction, kkissinger.

Of course the difference, so when the two frequencies are perfectly synchronised the difference is zero - this gives the zero beat point that you tune the theremin to.

Hopefully you can translate this all into a child-friendly explanation, Hels.

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