Subwoofer controller is quite simple, an input buffer provides phase switching and ensures that the input impedance of the source does not affect the filter performance, and this is nowfollowed by a 12dB/octave high pass filter. The phase reverse switch is used so that the sub can be properly phased to the rest of the system. If the mid-bass disappears as you advance the level of control, then the phase is wrong, so just switch to the opposite position.Contribute a better translation
The board has only one input, so if you plan to use a normal stereo feed supplying a single P48 board, you'll need to sum the two stereo outputs. This is easily accomplished by using a pair of resistors - the value should be between 2.2k and 4.7k. If this is done, replace R1 with either a 100 ohm resistor or a wire link.
The board has only one input, so if you plan to use a normal stereo feed supplying a single P48 board, you'll need to sum the two stereo outputs. This is easily accomplished by using a pair of resistors - the value should be between 2.2k and 4.7k. If this is done, replace R1 with either a 100 ohm resistor or a wire link.
VR1 is used to change the gain of the second integrator. The level through the controller can be set to make sure that there is no distortion - there can be a huge amount of gain at low frequencies, and if the gain is too high, distortion is assured!
The high-pass filter is designed as a peaking type, and gives a response that is almost perfect down to 20Hz. The lowest frequency can be tailored by changing C1, C2, C3 and C4. As shown, the response peaks at 18Hz, but you can use 68nF to increase this to 27Hz, or 47nF for 39Hz. See Table 1 for the full range of values.
The integrators (U2B and U2A) include shelving resistors (R8 and R11), and the capacitor / resistor networks (C3-R9, C4-R12) allow the HF attenuation to be halted at a specific frequency.
Important:
The unity gain frequency is important in only one respect - it will determine the internal gain of the system, and needs to be set based on the input signal level. If the unity gain frequency is set to (say) maximum (68Hz) and you have a 1V RMS input, then a 1V RMS input at 20Hz will severely clip the integrators. The setting for VR1 is determined by the input sensitivity of your power amplifier(s) used on the main system. It is probably easier to experiment a little than try to measure everything.
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