Obviously, we did not shelve it right away since there seemed to be no permanent effect. Some people were really creeped out after they had been exposed in my first try. But this is an engineering lab, so soon enough the lab was filled with cowboys wanting to experience it and trying to figure out how it works. Meanwhile, the more safety minded people took a short break and went for some air outside.
We stopped after the professor figured out something odd was going on on his floor.
Let's hope your PhD wasn't imaginary either, cue "science reproducibility crisis".
I am not sure what causes the other sounds to sound dampened, I figured it had something to do with how the ear works, that the sounds were physically still there.
But it is easy enough to try. Get a speaker or transducer rated for ultrasonic frequencies, and pump it with enough power that would make a real speaker sound painfully loud.
Since many of these robots use ultrasound locators based on echolocation to find other robots, we want to eliminate those from detecting us. One of the strategies we wanted to try, was to generate sound at the right frequency ourselves, which should completely ruin those sensors, thus making us invisible for no apparent reason.
So I bought a transducer used to clean ships, which was rated for use around the correct frequency. I connected it to a signal generator at an ultrasound frequency and wanted to test its effect on the echo sensor.
Now, I am doing this sitting in a noisy lab with a bunch of noisy instruments, robots whirring and computer fans. Some other people in a corner chatting away.
I put the transducer in front of the distance sensor, set up the program to print the distance measured, turn on the signal generator, and the whole room goes eerie silent.
I turn it off, and luckily the sound comes back immediately. It appears that if you pump 100+ decibels of ultrasound in a room, it actually drowns out other noise! This thing was quite powerful. After all, it was made for cleaning ships from foul.
At that point, I do realise I have no idea whether this is a safe thing to do for my hearing (and that of the audience), and shelve the idea. But I remember the split second where I thought I made myself and everyone else in the room deaf.