Separate power amplification for tweeter and woofer circuits—reduces crosstalk and harmonic distortion. Essential for accurate monitoring in post-production suites.
On the dubbing stage, the power supply for the high-frequency and low-frequency ranges is separated not out of nostalgia – but because each frequency range has completely different requirements for power stability and impedance behavior. A woofer draws current in bursts, especially during explosions or orchestral passages. A tweeter requires precise, fast voltage regulation for clarity. If both run through a single amplifier, the bass modulates the power rail, and the treble becomes muddy – particularly critical for the control of sibilants and spatial sound.
The practical implementation: two separate power amplifiers, or – in modern digital systems – two DSP channels with independent power supplies. The AES/EBU feed is split in the processor into high-pass and low-pass chains. Each range gets its own power amp with an independent transformer secondary winding, ideally from separate circuits. This sounds complex, but it's standard on any dub stage worth its salt – and the reason why mixes approved there can sound harsh on playback systems.
In dubbing, bi-wiring is also a prerequisite for acoustic measurement: when working with RTA or impulse response tools, you can adjust treble and bass independently without phase problems or clipping effects in one range damaging the other. This saves hours in room optimization. Some stages go even further – tri- or quad-amping for separate subwoofers, midrange, and presence bands – but that's more of a special case for cinemas with extreme requirements.
Warning: Bi-wiring requires clean crossover design and precise phase alignment between the paths. An incorrectly calibrated system with separate amps will sound worse than a simple single-amp setup. Therefore, this is always verified by the sound engineer with a measurement microphone and phase analyzer – not by ear.