A 6dB cut-off slope reduces the signal level by 6dB for every octave above or below the crossover frequency. In contrast, a 12dB cut-off slope reduces the signal level by 12dB for every octave. This means that a 12dB cut-off slope has a steeper roll-off than a 6dB cut-off slope, resulting in less overlap between the subwoofer and the other speakers in the system.
The choice between a 6dB or 12dB cut-off slope depends on several factors, such as the size and type of speakers, the room acoustics, and personal preferences. In general, a 12dB cut-off slope is better for larger speakers and rooms, as it provides more precise control over the frequency response. However, a 6dB cut-off slope may be sufficient for smaller speakers and rooms, and may produce a more natural-sounding transition between the speakers. Ultimately, the best choice will depend on the specific audio system and listening environment.