Abstract: An audio system for use in a confined space comprises N acoustic transducers, where N is an integer and N?2. Each acoustic transducer is configured to receive an audio signal for a respective channel of the audio system and to generate an acoustic signal therefrom, and is operably coupled to a respective filter having a phase response. The phase response of at least one of the filters is different from the phase response of at least one other of the filters at a frequency f having a corresponding wavelength ?=d/(n+½), where n is an integer and n?0 and d is a characteristic separation of two or more of the N acoustic transducers when in the confined space. Compensation is thereby achieved for a reduction in acoustic power that would otherwise occur over a range of frequencies of width ?f around frequency f.

Abstract: An audio system for use in a confined space comprises N acoustic transducers, where N is an integer and N?2. Each acoustic transducer is configured to receive an audio signal for a respective channel of the audio system and to generate an acoustic signal therefrom, and is operably coupled to a respective filter having a phase response. The phase response of at least one of the filters is different from the phase response of at least one other of the filters at a frequency f having a corresponding wavelength ?=d/(n+½), where n is an integer and n?0 and d is a characteristic separation of two or more of the N acoustic transducers when in the confined space. Compensation is thereby achieved for a reduction in acoustic power that would otherwise occur over a range of frequencies of width ?f around frequency f.

Abstract: A data encoding device has a serial data input and an encoded serial data output. The serial input is supplied to an encoding unit which combines each input bit with a plurality of additional encoding bits, to derive an encoded output bit and a plurality of updated encoding bits. The function performed by the encoding unit is selected such that over time the encoded output bit stream comprises substantially white noise. The output has constant and flat frequency response, so that the output of the encoding device is merely noise in the absence of an appropriate decoding device.