I've recreated this experiment which my school friend & I did around 30 years ago.
I've set up 2 reel to reel tape recorders where on the left "1963 Truvox" is set to record and supply the tape & the other "1959 Brenell 3 Star" is set for playback and take up.
In this configuration it'll create a crude echo machine, where I say something on the Truvox and a few seconds later it will come out in the Brenell.
I also created what sounds like a delay feedback effect by first saying some words and immediately placed the microphone at the Brenell loudspeaker and leaving it there. This keeps looping the last words I've said over & over again until the sound is distorted as analogue sound always contains noise.
The blue and yellow microphones is to record the audio from the tape recorders to my computer in seperate left and right audio channels (Truvox left speaker and Brennel on the right)