An electronic device comprises a speaker protection module (36) arranged to receive an audio signal (22) and to use one or more parameters relating to a loudspeaker to produce a controlled audio signal (34). An amplifier (40) is arranged to amplify the controlled audio signal to produce an amplified audio signal (24, 26) which is passed to the loudspeaker. The amplitude of the controlled audio signal (34) is such that the amplified audio signal (24, 26) is less than or equal to an amplitude determined to be safe for the loudspeaker in view of the one or more parameters. An ultrasound generator (16) is arranged to generate an ultrasound signal (30) that is mixed (32) with the controlled audio signal (34) before the controlled audio signal (34) is passed to the amplifier (40). The ultrasound generator (16) is capable of producing said ultrasound signal at a plurality of frequencies.