A receiver-audio-device and a transmitter-audio-device. The receiver-audio-device comprises a receiver-ultrasound-receiver, configured to receive transmitter-ultrasound-signals representative of a request, from a transmitter-audio-device, for complementary audio resources; and a receiver-processor, configured to generate a complementary-audio-output-signal based on at least the transmitter-ultrasound-signals and to provide the complementary-audio-output-signal to a receiver-loudspeaker. The receiver-loudspeaker is configured to provide a complementary-audio-output based on the complementary-audio-output-signal. The transmitter-audio-device, comprising: a transmitter-ultrasound-transmitter, configured to provide transmitter-ultrasound-signals representative of a request for complementary audio resources; a transmitter processor, configured to generate an audio-output-signal and to provide the audio-output-signal to a transmitter-loudspeaker. The transmitter-loudspeaker is configured to provide an audio-output based on the audio-output-signal.