The Whise®Profunder FFX 25 is a high quality active fixed frequency stereo crossover providing accurate stereo division of low and high frequency audio signals. The precision alignment ensures a seamless interface across the whole audio spectrum. 
The design uses a patent-pending Neville Thiele Method (NTM) filter providing a greater than 100dB/octave crossover profile delivering constant amplitude summing and sound pressure level across the critical crossover region. This feature enables full integration of sub-bass units such as theWhise Profunder seriesinto any sound system. Advantages include increased headroom and reduced distortion on the companion mid/high frequency loudspeakers.
The electronic design also includes an NTM high-pass filter set to 14Hz (or specify). This acts as an infrasonic filter to reduce inter-modulation distortion and protect sub bass speaker systems.

The Profunder FFX 25 is designed for unity gain on the main outputs however the low frequency output has a variable gain and phase normal/inverse control. This is adjustable from 0 to +6db gain/phase inverse to cater for systems having different sensitivity and/or output phase design. For sound reproduction systems with mono bass, a mono input bass switch is provided to sum the two channels.
The Profunder FFX 25 is normally shipped with a fixed 100Hz or 80Hz crossover frequency but other frequencies can be factory set (between 70 -150Hz) upon request. The unit has a delayed "turn on" muting circuit to prevent transients.