172345 ⎘
Direction-finders for determining the direction from which infrasonic, sonic, ultrasonic, or electromagnetic waves, or particle emission, not having a directional significance, are being received using ultrasonic, sonic or infrasonic waves; Systems for determining direction or deviation from predetermined direction using amplitude comparison of signals derived from receiving transducers or transducer systems having differently-oriented directivity characteristics wherein the signals are derived simultaneously derived from different combinations of signals from separate transducers comparing sum with difference