An aerosol-generator (100; 200; 400) for an aerosol-generating device, the aerosol-generator comprising: a surface acoustic wave atomiser comprising: at least one substrate comprising an active surface defining at least one atomisation region (116, 117); a first transducer positioned on the active surface of the at least one substrate; and a second transducer positioned on the active surface of the at least one substrate; a first supply element arranged to supply a first liquid aerosol-forming substrate to the at least one atomisation region; a second supply element arranged to supply a second liquid aerosol-forming substrate to the at least one atomisation region; and a controller, wherein the controller is configured to provide a first drive signal to the first transducer for generating surface acoustic waves on the active surface of the at least one substrate, wherein the controller is configured to provide a second drive signal to the second transducer for generating surface acoustic waves on the active surface of the at least one substrate, wherein the controller is configured to provide the first drive signal to the first transducer only when the first liquid aerosol-forming substrate is supplied to the at least one atomisation region by the first supply element, and wherein the controller is configured to provide the second drive signal to the second transducer only when the second liquid aerosol-forming substrate is supplied to the at least one atomisation region by the second supply element. a surface acoustic wave atomiser comprising: at least one substrate comprising an active surface defining at least one atomisation region (116, 117); a first transducer positioned on the active surface of the at least one substrate; and a second transducer positioned on the active surface of the at least one substrate; at least one substrate comprising an active surface defining at least one atomisation region (116, 117); a first transducer positioned on the active surface of the at least one substrate; and a second transducer positioned on the active surface of the at least one substrate; a first supply element arranged to supply a first liquid aerosol-forming substrate to the at least one atomisation region; a second supply element arranged to supply a second liquid aerosol-forming substrate to the at least one atomisation region; and a controller, wherein the controller is configured to provide a first drive signal to the first transducer for generating surface acoustic waves on the active surface of the at least one substrate, wherein the controller is configured to provide a second drive signal to the second transducer for generating surface acoustic waves on the active surface of the at least one substrate, wherein the controller is configured to provide the first drive signal to the first transducer only when the first liquid aerosol-forming substrate is supplied to the at least one atomisation region by the first supply element, and wherein the controller is configured to provide the second drive signal to the second transducer only when the second liquid aerosol-forming substrate is supplied to the at least one atomisation region by the second supply element.