I use a passive level control of my own design, -10db is about 6.7kΩ in series with the CD player driving a Force sub with 10kΩ nominal impedance in parallel with main amp.
I used it with a Parasound A23 which also has 33kΩ input impedance. Currently driving a NuPrime ST-10 with 23.5kΩ impedance. Measured output is flat in both cases.
See http://www.ielogical.com/Audio/#LastHurrah
However, I would not recommend using the HiPass feature of any subwoofer. IMO 4th order Linkwitz-Riley filter in the very region where the mains are beginning to fade is not the best solution and creates difficult to integrate slope and phase issues, particularly with 3rd party subs. See http://www.ielogical.com/Audio/#Basement. No mention is made of the main speaker capability, but unless they already have substantial low end capability, the lowish 130Hz E112 corner frequencies would give me pause. My experience has found that a simple passive XO for the mains and integrating a sub with higher corner, lower order filters on its own may be a better solution as there is a wider region for ’melding.’ Steep filters can be problematic with a sub and mains cut from divers sonic cloths.
See http://www.ielogical.com/Audio/SubTerrBlues.php for more.
I used it with a Parasound A23 which also has 33kΩ input impedance. Currently driving a NuPrime ST-10 with 23.5kΩ impedance. Measured output is flat in both cases.
See http://www.ielogical.com/Audio/#LastHurrah
However, I would not recommend using the HiPass feature of any subwoofer. IMO 4th order Linkwitz-Riley filter in the very region where the mains are beginning to fade is not the best solution and creates difficult to integrate slope and phase issues, particularly with 3rd party subs. See http://www.ielogical.com/Audio/#Basement. No mention is made of the main speaker capability, but unless they already have substantial low end capability, the lowish 130Hz E112 corner frequencies would give me pause. My experience has found that a simple passive XO for the mains and integrating a sub with higher corner, lower order filters on its own may be a better solution as there is a wider region for ’melding.’ Steep filters can be problematic with a sub and mains cut from divers sonic cloths.
See http://www.ielogical.com/Audio/SubTerrBlues.php for more.