individual speaker polarity is detected by band - limiting the processing to a range where the impulse response of most speakers are in - phase with their wiring . in the preferred embodiment , a second order 400 hz low pass filter is used to band - limit the processing . filtering can occur prior to processing as part of the noise generation , or completely as a post - processing operation on a full - bandwidth impulse response . applying the low pass filter eliminates artifacts in the impulse response due to reverse - polarity wired drivers in a speaker system . by analyzing only the lower frequencies , the initial peak of the impulse response will correlate to speaker polarity in the system .