Infact I've been wondering about this for some time. How to get an adjustable (line level) highpass, for cheap and preferably universal in use, since it's a very rare feature on actual hifi gear?
Option 1: DIY. You could easily build a cheap DIY box that has inline capacitors acting as a highpass between preamp and poweramp. For example use 2-pole 6-position rotary switch (cheap) to select between 6 crossover frequencies, or 5 plus defeat. Easy to calculate. Would even work for balanced signals, although I'm not sure what influence the cap tolerance would have on a balanced signal. Unbalanced, this is of no concern and should work fine.
Disadvantage: you need to adjust cap values for your particular preamp output impedance and amp input impedance. As soon as you exchange gear and these values change, you literally need to recalculate and recap the thing. Also you're limited to a -6dB/octave rolloff. Depending on speaker characteristics, this could be fine, or not. Certainly the weakest filter slope. The whole approach is really only feasible for the electronically inclined. For average customers and listeners it's not an option.
Option 2: Subwoofer with highpass built into the line-level passthrough. Active and 12dB/oct, The easiest king's way, IF: the usually fixed frequency fits your needs. Which more often than not, it doesn't. My old subwoofer highpassed at 50Hz and that was fine because the (large 8") satellites did 50Hz easily, but generally you'll want it to be adjustable. Most subwoofers today don't even offer any highpass functionality, and I've never seen any that has it adjustable. If you're lucky, it works fine, in most cases it doesn't.
Option 3: professional crossovers. Think analog Behringer Super X Pro thingies, or the DSP versions. Certainly still affordable at 120-300 for stereo. Fully adjustable, in case of DSP version even more so. The usual MiniDSP suspects are a bit more, but not much.
Overall, I really think there's only two options that make sense. 1) the super cheap DIY box if you're good at calculating and building such things and a mere 6dB slope works for your needs, and 2) full active crossover with all features. For people with little money the price may be somewhat steep for a mere filter, but it's really worth it. Hell, a 3-way DSP crossover for 300-500 moneys also doubles as a 3-way loudspeaker development kit.
Option 1: DIY. You could easily build a cheap DIY box that has inline capacitors acting as a highpass between preamp and poweramp. For example use 2-pole 6-position rotary switch (cheap) to select between 6 crossover frequencies, or 5 plus defeat. Easy to calculate. Would even work for balanced signals, although I'm not sure what influence the cap tolerance would have on a balanced signal. Unbalanced, this is of no concern and should work fine.
Disadvantage: you need to adjust cap values for your particular preamp output impedance and amp input impedance. As soon as you exchange gear and these values change, you literally need to recalculate and recap the thing. Also you're limited to a -6dB/octave rolloff. Depending on speaker characteristics, this could be fine, or not. Certainly the weakest filter slope. The whole approach is really only feasible for the electronically inclined. For average customers and listeners it's not an option.
Option 2: Subwoofer with highpass built into the line-level passthrough. Active and 12dB/oct, The easiest king's way, IF: the usually fixed frequency fits your needs. Which more often than not, it doesn't. My old subwoofer highpassed at 50Hz and that was fine because the (large 8") satellites did 50Hz easily, but generally you'll want it to be adjustable. Most subwoofers today don't even offer any highpass functionality, and I've never seen any that has it adjustable. If you're lucky, it works fine, in most cases it doesn't.
Option 3: professional crossovers. Think analog Behringer Super X Pro thingies, or the DSP versions. Certainly still affordable at 120-300 for stereo. Fully adjustable, in case of DSP version even more so. The usual MiniDSP suspects are a bit more, but not much.
Overall, I really think there's only two options that make sense. 1) the super cheap DIY box if you're good at calculating and building such things and a mere 6dB slope works for your needs, and 2) full active crossover with all features. For people with little money the price may be somewhat steep for a mere filter, but it's really worth it. Hell, a 3-way DSP crossover for 300-500 moneys also doubles as a 3-way loudspeaker development kit.
