Reverb (or reverbaration) is for sure one of the oldest audio effects known to humanity. Many ancient buildings were built specifically to use reverb to amplify the sound coming from the podium or stage so larger audiences could hear someone talk, or play music. Some examples of this are ancient (amphi-)theaters and churches / cathedrals. Of course, modern opera houses or similar locations also take reverb into account when designing the building. But what if you were an audio engineer in the early days of recording, before every effect could be produced digitally, and didn't have access to such a building to record sounds for film or music? After all, any sound, recorded without reverb, will sound unnatural to the listener, since we're all used to experiencing sound with some natural reverb. Well, you could use your bathroom as a "reverb machine". Or you get a large metal plate, hang it up on flexible suspensions, deploy the sound to it via a speaker, and record the vibrations of the plate. That's one widely used solution anyway (even today!). The plate acts as "2-dimensional" room where the sound travels along the surface and reflects off the sides. The effect can even be modified depending on the position of the speaker and the sound pickups, the size of the plate, dampeners put in different locations of the plate, tightness of the suspensions etc.. Just something I found interesting, have a good day.