Flower speaker

I have seen a speaker like this in other videos.

How does it work? Is the voice coil in the base?  Does it sound great with a theremin?  

I'm guessing that this old RCA instrument has the speaker amplifier built in?

https://www.youtube.com/watch?v=4n4JzBwR62Y

"How does it work? Is the voice coil in the base?"  - DanielMacKay

Yes, the voice coil is in the base.  In general, exponential horns act as impedance matching transformers.  The movement of the diaphragm is usually small and low impedance, while the movement of the air you want is large and high impedance.  The problems with horns is that they need to be really huge to work over the full range, and since the mouth of the horn is then also huge, the high frequencies get "beamy" or very directional.  The solutions are to use multiple sized horns, much like a 2 or 3 way stereo speaker, or use horns just for the higher end.  Even these smaller horns can have directional problems, and one solution there is to "pinch" the horizontal dimension while compensating with the vertical dimension to keep the overall flare exponential.

The reason you see horns on really ancient audio equipment is because of their high efficiency, not their high fidelity.  A horn like that pictured will likely have a strong resonance, and the bass will drop like a rock once you pass the point at which the horn can couple effectively.

You see horns in modern PAs covering the mids and highs, and here the "beaminess" of the horns can help control the coverage pattern.  But you still need super hefty wattage to cover the non-horn loaded low end.

I'm sure you could use one or more filters to emulate the response, it would be much like setting up a tuba or trumpet voice in a synth.

> high efficiency, not their high fidelity

But, this one sounds lovely!  or do you think that it's there only for decoration? do you think the theremin is being fed directly into the mixer board?

The speaker behind the head is a form of pitch preview and not generating the sound the audience is hearing or a Thereminist would walk away deaf. Most likely in the video you hear a $$$ post sound processing technique. I have found that how someone generates a beautiful sound is held close to the vest. The speaker in the video I believe is beautiful yet more ornamental to reflect the period.

To improve theremin sound it may be better to develop it acoustically before going directly to the sound card.

Christopher

I'm thinking the entire video may be a "lip-sync" re-enactment of a recording done under more ideal sonic circumstances.