Are You Old Enough to Remember Those Jaw-Dropping Manufacturer Demos?

I saw the Dual turntable demonstration you described.  It wasn't the playing upside down that was amazing to me.  It was the huge up and down motion of the spring-hung table.  The motion was smooth, so that is why the playing was not disturbed, but it was still quite amazing to see.

The other gimmick demonstration I recall was at a dealership selling Bose speakers.  They had a box speaker mounted on the wall that was about two feet tall by about 16-inches wide, by 8" or so deep.  It did not sound particularly good, but, it was plenty loud.  The person presenting the speaker then press a button on a remote control and the speakers on the wall, which were dummies, opened up to reveal some extremely tiny speakers hidden inside the box that were doing the actual playing.  Cute.

Another impressive demonstration was not one with any gimmicks, but, it was still quite a show.  It was the first demonstration of the Hill Plasmatronic speaker (ionic tweeter that uses an electrode to ionize the air around the electrode to create a plasma that expanded and contracted to generate sound).  The speaker was a scary looking thing that was attached to a 100 lb canister of nitrogen gas (the gas is fed into the area around the electrode to create an ionized nitrogen plasma; if nitrogen was not employed, oxygen would be ionized in sufficient quantities to create a large quantity of ozone which is bad for one's health and would quickly corrode and destroy the electrode in the tweeter).  The plasma glowed a blue color which was fascinating and pretty to look at.  You could faintly smell ozone even with the nitrogen gas feed.

I recall the upside-down turntable demo.  For me it was at a hifi show in Philly during the early 1970s.  

I don’t know if you would call it a gimmick but the best demonstration at a hifi show for me was at a DC show in the spring of 1970.  The good folks at Dynaco were demonstrating the new A25 speakers by hiding them behind a screen that covered the entire side of the room.   After playing a song or two, someone turned on some lights on the other side of the screen showing the speakers.  I was amazed by how entire wall seemed full of sound and gave no hint as to where the speakers were located.  I was so impressed that I bought a pair of A25 within a week.  The A25 can still hold its own today.   Truly a classic design.

At Capital Audiofest, a few years ago, a local D.C.-area dealer set up a room with a really tiny tube amp, a laptop for a source, and tiny ProAc Tablettes for the speaker.  A lot of people commented on how great that modest system sounded.  The first thing most listeners did when entering the room was to look for the subwoofers; there were none.  What was hidden was the DAC used in this setup.  It was an Audio Note DAC 5 Signature that cost more than ten times the rest of the entire rest of the system.