I would like to hear your advice on which method to use to transmit music or speech in a frequency band that is sensitive to the human ear up to 3km. Everyone knows that the higher the frequency, the sharper the directivity, but instead, the attenuation in the air is severe. The Ganasys company, which made LRAD, dismissed the fact that it used ultrasonic waves as an erroneous view and said that it actually uses the sensitive 2200~3300Hz audible band. Meanwhile, ZaellixA piqued my curiosity by suggesting that ultrasonic waves can be used to modulate audible sounds to transmit sound with ultrasonic characteristics farther away. Is there really no other way than to modulate with ultrasound?