An acoustic system comprising: a headphone device (1, 1a); and a loudspeaker device (2, 2a), the headphone device being configured to receive sound data through wireless communication from a sound output device (4, 5), and the headphone device comprising an output control unit (17, 17a) that is configured to transmit the sound data to the loudspeaker device if the headphone device and the loudspeaker device are connected to each other, and the headphone device being configured to output a sound from a headphone, and the loudspeaker device comprising an output control unit (32, 32a) that is configured to cause a sound to be output from a loudspeaker if the headphone device and the loudspeaker device are connected to each other, the sound being generated based on the sound data transmitted from the headphone device, wherein a connection between the headphone device and the loudspeaker device comprises a connection using non-contact communication, wherein the output control unit of the headphone device is configured to transmit the sound data to the loudspeaker device and to cause the sound based on the sound data to be output from the headphone, if the headphone device and the loudspeaker device are connected to each other through the non-contact communication, wherein the output control unit of the headphone device is configured to change a ratio between a first volume and a second volume according to a distance between the headphone device and the loudspeaker device, the first volume being a volume of sound based on sound data to be transmitted to the loudspeaker device, and the second volume being a volume of sound based on sound data to be output from the headphone. a headphone device (1, 1a); and a loudspeaker device (2, 2a), the headphone device being configured to receive sound data through wireless communication from a sound output device (4, 5), and the headphone device comprising an output control unit (17, 17a) that is configured to transmit the sound data to the loudspeaker device if the headphone device and the loudspeaker device are connected to each other, and the headphone device being configured to output a sound from a headphone, and the loudspeaker device comprising an output control unit (32, 32a) that is configured to cause a sound to be output from a loudspeaker if the headphone device and the loudspeaker device are connected to each other, the sound being generated based on the sound data transmitted from the headphone device, wherein a connection between the headphone device and the loudspeaker device comprises a connection using non-contact communication, wherein the output control unit of the headphone device is configured to transmit the sound data to the loudspeaker device and to cause the sound based on the sound data to be output from the headphone, if the headphone device and the loudspeaker device are connected to each other through the non-contact communication, wherein the output control unit of the headphone device is configured to change a ratio between a first volume and a second volume according to a distance between the headphone device and the loudspeaker device, the first volume being a volume of sound based on sound data to be transmitted to the loudspeaker device, and the second volume being a volume of sound based on sound data to be output from the headphone.