Little bit of science
Some experimenters in the 1840's
claimed that they could focus coldness
with a parabolic reflector. I decided to try it in an extremely casual setup....
The cold source is one of those 'contained ice' things, taken out of the freezer, surface temp around zero. It certainly radiates coldness. You can feel the coldness near it, and the thermocouple near it gets down to 50.
I tried a flat foil reflector and a parabolic reflector shaped around a bowl.
The thermocouple showed no variation from room temperature near or far from the flat reflector, and no variation anywhere in the parabolic. There was no 'focal point'.
The original author describing those experiments thought they were fooled by artifacts, and now I'm convinced he's right!
= = = = =
Later: Since I had this parabola in hand, decided to try it with sound. How much difference does it make? Using Audacity to generate a 1k tone and then white noise, I held up my GenRad SLM and put the bowl in front of it, varying distance. It didn't make much difference for white noise, maybe 2dB. It made a noticeable difference on the 1k tone, about 6dB. The 'focal point' was the loudest placement. So the parabola isn't 'focusing' sound in a geometrical sense, it's just serving as a resonator. Tried to spot the resonances with a long rising tone, and nearly got dizzy. The ROOM has several sharp resonances, slamming the SLM needle up and down, and flipping back and forth between my ears as the tone rises for 30 seconds. Jesus. Won't do that again. My tinnitus is still flipping back and forth. [Hmm. That's the only interesting result from this mess. Dynamic afterimages in tinnitus.]
Here's the rising tone in MP3 form.
Don't sue me if you get dizzy. You have been warned.
Tinnitus is often believed to be a simple numbness from damaged hair cells, parallel to the buzzing you get from skin nerves after sitting or laying in one position too long. This observation ruins the belief. If tinnitus can form afterimages repeating the rhythm of a stimulus, it must be happening WAY up in the auditory chain, maybe in the intonation-sensing areas of Broca.