DIY horn lens?

Found one in a thread which has me very intrigued.
Has anyone built their own lens for their horn tweeter/mid?

I've got a variety of spare piezos for experimentation until I produce a lens worthy of a quality horn. I suppose the ideas and material types are unlimited. I'm going to start by slicing some super thin strips of poplar and cultivating some architectural and encasement designs from there. I propose some card stock thick pieces formed/glued into a horn configuration then adhered to the resonator disc and mounted to an encasement to serve as a passive radiator.
 
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I've used successfully two old 6 1/2" paper cones (7 1/2 total with basket), with some kind of plaster in the front ad hot glue in the back to stiffen and make a good waveguide for a 2" paper tweeter ,Fc at about 1500 Hz . Also for that purpose ,I have two old 5 1/2" cones that I want to put together with a modern 1" titanium tweeter ,even if it has already a metal curved flange...a little bit difficult ,for a Fc at 2500 Hz . Geometry and distance from mouth to throat is important ,and also diameter determines at which frequency the horn (also wg) makes effects .
 
I've got a few metal objects to try. One a paper thin shell of an insulated coffee cup. Another the same diameter and half the height of a tiny dixie cup.

Aside from the super thin wood slices formed into a waveguide shaped cone, I'm going to try paper mache and see what different shapes do with the sound. My theory is it will get a lot more volume out of the piezos I'll be experimenting with and deliver discernible mids that tend to be wispy with piezos.
 
*UPDATE*

Some interesting personal discoveries I made with my piezo experiments.

The lens/horn is responsible for sound texture and the cone responsible for frequency reproduction and volume.

I have to accredit the plastic being the reason so many people frown at the sound and use of piezos. The plastic makes them sound plastic.

Upon using my own cones I found a larger cone drops highs and turns the speaker into a much more productive midrange horn. Oddly, a cone lacking density doesn't produce much volume and a cone that's overly dense doesn't produce much volume. I'll have to do some caliper readings on stock cones but density and thickness greatly control the volume at any applied wattage.

Ultimately I'm seeing that with a more dynamic, well thought out cone and lens material and design, piezos could serve as dedicated midrange speakers eliminating the need for a crossover or impedance matching.
I have to assume someone has done this but asks for more money than any of us believe piezos are worth so they never caught on.
Just the same, it can be very affordable and effectively done in your own shop.

As either a tweeter or midrange these cheap little discs have so much more to offer than the people manufacturing them bother with.