For those who don’t know what notch filter is I’ll explain in short: the task of a notch filter is to reduce the strength of the audio signal in certain frequency range. Such a filter is usually used in a single driver (also known as broadband or full-range) speaker designs. Because it has only one driver it is often very hard or impossible for such a speaker to convey a flat response along the whole length of the frequency spectrum. Usually such a speakers emphasize certain frequencies that leads to tonal colourations.
It is strange how often it happens to me to change something in the audio system while experimenting and to notice an improvement. I enjoy the achieved result for some time but then I decide to restore the system to its initial state, only to realise that the so called “improvement” is nothing else but an effect that actually departs the reproduction from its authentic character.