Is parametric speaker a nuisance or a weapon in disguise?
Take a parametric speaker. Take it three apartments above yours. Nearly at 75 percent volume, place it face downwards, but not floor, ask someone to hold it. Now play music on another regular bluetooth speaker in front of it. Do not play anything on parametric speaker. Just play music on regular speaker adjacent to it. Do not face regular speaker downwards. Play music on regular speaker, rather pocket size bluetooth speaker like JBL Go, on 25 percent volume. Results would be good if someone holds those speakers together and does not place parametric speaker on floor. Hold the parametric speaker face down at 75 percent volume. Hold regular speaker face towards parametric speaker. When nothing is playing on parametric speaker, it still emits ultrasonic waves. You can listen to the music at the exact spot three floors below. And this cannot be blocked. No soundproofing solution can block this.