A speaker apparatus comprising: two or more speaker units that are arranged in a speaker housing ; a sensor microphone that is arranged in said speaker housing and outputs a sound collection signal; target unit selection means adapted to select one of said speaker units as a target unit; sound signal supply means adapted to supply an input sound signal to said target unit; error detecting means (25; 32) adapted to provide an error output; characterized in that the speaker apparatus further comprising: a band elimination filter that attenuates a frequency component in a test band , and thereby generates a non-target sound signal from said input sound signal; a first bandpass filter that attenuates all frequency components in all bands other than said test band , and thereby generates a reference sound signal from said input sound signal; and a second bandpass filter that attenuates all frequency components in all bands other than said test band , and thereby generates a detection sound signal from said sound collection signal , wherein: said sound signal supply means also supplies said non-target sound signal to the speaker units other than said target unit; and said error detecting means (25; 32) makes a comparison between said detection sound signal and said reference sound signal , and on a basis of a result of the comparison, provides said error output. two or more speaker units that are arranged in a speaker housing ; a sensor microphone that is arranged in said speaker housing and outputs a sound collection signal; target unit selection means adapted to select one of said speaker units as a target unit; sound signal supply means adapted to supply an input sound signal to said target unit; error detecting means (25; 32) adapted to provide an error output; characterized in that the speaker apparatus further comprising: a band elimination filter that attenuates a frequency component in a test band , and thereby generates a non-target sound signal from said input sound signal; a first bandpass filter that attenuates all frequency components in all bands other than said test band , and thereby generates a reference sound signal from said input sound signal; and a second bandpass filter that attenuates all frequency components in all bands other than said test band , and thereby generates a detection sound signal from said sound collection signal , wherein: said sound signal supply means also supplies said non-target sound signal to the speaker units other than said target unit; and said error detecting means (25; 32) makes a comparison between said detection sound signal and said reference sound signal , and on a basis of a result of the comparison, provides said error output. a band elimination filter that attenuates a frequency component in a test band , and thereby generates a non-target sound signal from said input sound signal; a first bandpass filter that attenuates all frequency components in all bands other than said test band , and thereby generates a reference sound signal from said input sound signal; and a second bandpass filter that attenuates all frequency components in all bands other than said test band , and thereby generates a detection sound signal from said sound collection signal , wherein: said sound signal supply means also supplies said non-target sound signal to the speaker units other than said target unit; and said error detecting means (25; 32) makes a comparison between said detection sound signal and said reference sound signal , and on a basis of a result of the comparison, provides said error output. said sound signal supply means also supplies said non-target sound signal to the speaker units other than said target unit; and said error detecting means (25; 32) makes a comparison between said detection sound signal and said reference sound signal , and on a basis of a result of the comparison, provides said error output. <EOS>