Active noise cancellation system for a helmet

An active noise cancellation (ANC) system for a helmet, for attenuating sound pressure in a first frequency range in a defined spatial region at a first side of the helmet, the ANC system comprising:

• a plate, a first face of the plate configured to be disposed, in use, against an inner surface of the helmet to form, with the helmet, a chamber, such that the plate forms a first wall of the chamber and the inner surface of the helmet forms a second wall of the chamber;
• a loudspeaker provided on the first face of the plate such that, when the plate is mounted on the helmet, the loudspeaker is within the chamber, the plate comprising an aperture for allowing transmission of sound from the loudspeaker to the spatial region;
• at least one microphone for measuring the sound pressure;
• and
• an ANC control system for determining, based on output signals from the at least one microphone, a drive signal for driving the loudspeaker to generate a sound signal that at least partially attenuates, in the defined spatial region and in the first frequency range, sound signals from at least one noise source.