I’ve heard about Directional Microphones - which you can use to pick up noises from a certain direction and not get ambient or noise from around you, as far as I understand them.
Can you also get Directional Speakers? To some extent all speakers are directional, but generally they’re designed to emanate sound in a wide arc. Headphones would be more like this, in that they usually only face in one direction - but you can still hear the sound from them if you hold them at an angle, or away from your head.
Is it possible for me to have a speaker that “fires” sound to a person on the other side of a crowded room so that only they hear it and no-one else? I can’t think how to put this well, so it’d be as a lightbulb is to an LED pointer, as is speaker to “directional” speaker.
High-frequency speakers are directional, and you want them aimed at the listener. Bass sounds are not very directional, which is why some systems have a center channel for the subwoofer. I’ve heard that theoretically you can use a laser as a carrier for sound, making somebody’s shirt button into a speaker. I don’t know if it really works.
You can do even better than a beam. If you have an ellipsoidal dish, with your source at one focus, then the sound will only be heard strongly at the other focus, and not at any other point (even in the same direction). There are two spots in one of the halls in the U. S. Capitol Building, for instance, where a person at one spot can whisper and be heard by someone in the other spot, about a hundred feet away. Anywhere else in the hall, you’ll only hear it as well as you’d ever hear a whisper.
Similar effect on the Quad at the University Of Illinois in Champaign-Urbana (my alma mater). Stand at a particular spot at one end and speak in a normal voice, you can be heard hundreds of yards away at the other end due to geometry of the buildings at each end. Anywhere else you won’t hear the speaker.
IIRC from my speaker design books, “directionality” of sound is related to the wavelength - longer waves (lower notes) are much less directional while shorter waves are more directional. Dunno if this is strictly an indoors phenomenon though.
When I Googled “directional speakers,” this was the first hit I got.
I’ve seen speakers like these in museums, where they’re mounted near the ceiling and pointed straight down. This allows people standing in front of an exhibit to be inside a pool of sound that doesn’t spill out to other areas of the room the way a wall-mounted speaker would.
Yes, you can get speakers with different directional patterns, like those of microphones. They aren’t REALLY directional unless you horn-load them, but that tends to cause some problems and color the sound, and bass horns are enormous. You could maybe use a reflector, but only for higher frequencies and it wouldn’t be hi-fi, just as parabolic mics aren’t used for music recording.
Most speakers are monopolar, which means basically that each frequency band is covered by one driver, or several closely spaced drivers moving in the same directions, with boxes on the backs of the speakers. At low frequencies they are omnidirectional, like an omni mic, but they’re somewhat directional higher up in frequency. The directionality depends on the size of the driver and the “baffle” (the box front) in relation to the wavelength of the sound. The modern skinny tower speakers are made that way in part to disperse the sound more widely.
You can buy dipolar speakers, which either simply don’t have boxes, or they have drivers on the back that move in while the others move out and vice-versa. The sound cancels out to the sides, while the back gets sound out of phase with the front, and you get a figure-eight pattern. They aren’t as popular in part because they have to move more air to overcome that cancellation. Dipole woofers are really expensive for the sound you get out of them.
Heres the website of a guy who designs some dipolar speakers:
It has a lot of information about dipolar speakers, and audio in general. He also makes some omnidirectional speakers, and somewhere he talks about cardioid woofers, with heart-shaped radiation patterns like cardioid microphones.
That other product uses ultrasound and it’s pretty elaborate.
I forgot to mention that Yamaha now makes a product that uses a phased array of little speakers to form multiple sound beams that bounce off the walls and make surround sound from a single box, plus a subwoofer if you want bass.
