Abstract: An active acoustic system provides attenuation and spectral shaping of an acoustic wave. A phase lock loop (304) phase locks to the input acoustic wave (6) and generates (306) a desired signal or tone (308) in given phase relation therewith. An error signal (44) from an error transducer or microphone (16) is summed (302) with the desired signal (308) and the resultant sum is supplied to the error input (202) of an adaptive filter model (40) which outputs a correction signal (46) to an output transducer or speaker (14) to introduce the canceling and shaping acoustic wave. In other embodiments, various combinations sum the desired signal (308) with the error signal (44), the model output correction signal (46), and the model input signal (42). Speaker and error path compensation (146, 318, 320) and feedback compensation (340) is provided.