With 8 speakers, one in each corner, can a combination of waves be emitted that are silent from the sources but form a coherent emission somewhere between?
I mean that even if you walked around the room the sound of something, say a ball bouncing, would stay in the position that it sounds like its bouncing in relative to the walls and not because your position is being tracked and each speaker adjusts its volume accordingly, silencing as you approached and vice versa, but because the pressure changes in each speaker are beyond the 20 to 20k Hz range we hear until a combination of interference creates a wave that is formed at a controllable location and actually emits from there. An opposite to dead spots.
We have Phased arrays to steer sound without moving the array if we're not using the parametric array effect to 'beam' the sound but maybe some combination of these. Acoustic phase conjugations which can create a localized vibration or sound wall that could perhaps be enough of a non-linear medium to scatter the ultrasonic propagation? There is Intermodulation, primarily considered a distortion but all combined this could be possible?
Best Answer
Not in any practical sense, no.
Constructive/destructive interference can only change the amplitude at a given frequency; it cannot produce a frequency shift. Combining multiple ultrasonic signals will only give you another ultrasonic signal; it will never result in an audible frequency.
Audio "dead spots" are the result of multiple audio paths that happen to perfectly cancel out at that spot. They are, in a sense, "unstable", because the balance is only hit at that one exact location (and, in most cases, even then only at specific frequencies). At most other locations, the sound can be heard normally.
There's no way to get the opposite effect you're describing, of a set of signals that cancel out everywhere except one location. This is because there's no way to make signals cancel out everywhere, besides making them perfectly equal and opposite, and originating from the same point. (At which point, there's effectively no signal being transmitted at all.)
What is possible is to produce a single point of constructive interference, where a sound is perceived louder than it is elsewhere -- this is simply the opposite of the "dead spot" effect I described earlier. However, this doesn't translate to the effect you're describing: the sound is not re-emitted from that location; it can only be heard by a listener in that location, and they will hear it coming from all of its "real" sources.