In 1979 there was the Audio Pro A4-14 three-way active speaker with ACE-BASS. It was and still is a great speaker that people use and buy used today. I think the speaker and its constructor Karl Erik Stahl was way ahead of time.You must admit, the folks at Linn realized many years (decades) ago passive sucked. Their method of adding the crossover in the amp may not have been the best solution but it worked.
AES E-Library » Synthesis of Loudspeaker Mechanical Parameters by Electrical Means: A new Method for Controlling Low-Frequency Loudspeaker Behaviour
A method for extending bass response and lowering distortion in louspeaker systems, which differs from both equalized and servo or feedback systems, is described. It can be seen as an extension of the technique to increase loudspeaker damping by giving the driving amplifier a negative output...
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