The AKG BX-20E is a landmark in studio reverberation technology, known for its natural sound and advanced design. Released as a high-end spring reverb unit, it set itself apart from conventional systems by using AKG’s patented Torsional Transmission Line (TTL) principle. This method employs specially designed spring elements that recreate the complex reflections of real acoustic spaces with a high degree of realism. Unlike standard spring or plate reverbs, the AKG BX-20E produces reverberation free from flutter echoes, colouration, or feedback, resulting in smooth, dense, and musical ambience.
Designed as a fully stereo system, the AKG BX-20E includes two independent channels, each with its own spring system, amplifier module, and decay-time control. These decay times can be adjusted using a remote control unit, allowing for continuous variation from 2 to 4.5 seconds on each channel. The remote control uses motion-based feedback, enabling precise adjustments even during recording or mixing. The unit supports both independent and parallel input use, making it suitable for stereo or dual mono configurations.
Unlike many reverb devices, the AKG BX-20E outputs only the processed signal, with none of the original dry input mixed in. This ensures that the resulting sound remains clean and consistent, with no risk of phase interference or tonal shifts. The quality of reverberation is comparable to that of high-end plate units and even physical echo chambers, but with a distinct character that remains uniquely identifiable as a AKG BX-20E.
Inside the AKG BX-20E enclosure, each channel’s spring system is suspended using a single-point pendulum mount. This design isolates the springs from floor vibrations and nearby sound sources, allowing the unit to be installed in control rooms or near monitors without causing unwanted resonances. No additional mounting, shock absorption, or acoustic isolation is required.
The TTL system delivers a high density of resonant frequencies and pulse reflections, replicating the randomness and complexity of natural environments. It also offers a frequency-dependent decay curve, which creates a more realistic and musically useful reverb character. The linear frequency response ensures that the reverb effect remains consistent across the entire audible spectrum.
Other features of the AKG BX-20E include user-adjustable input sensitivity, switchable mono input operation, and built-in limiters on each channel to prevent input overload. The AKG BX-20E also provides a delay of 20 to 50 milliseconds between signal input and the onset of reverb, simulating the natural time gap between direct sound and reflections in physical spaces. Decay-time settings are silent in operation, making adjustments practical during live sessions without introducing noise.
The AKG BX-20E requires no regular tuning, calibration, or maintenance, and is engineered for long-term reliability. It operates on 120 or 220 volts AC, or 24 volts DC, making it compatible with a wide range of studio setups.
The AKG BX-20E remains one of the most respected reverb units ever built. Its unique sound has appeared on countless records across decades and continues to be prized for its warmth, clarity, and spacious depth. Many modern reverb plugins and processors attempt to replicate its sonic signature, but the original hardware remains the standard by which others are judged.
Features
- High density of resonant frequencies
- High pulse density to duplicate the many sound paths of a naturally reverberant environment
- High degree of statistical diffusion in both frequency and time domains
- Linear frequency response for maximum range of applications
- Precise duplication of natural room-reverberation effects
- 20–50 msec delay between excitation and onset of reverberation
- Remote control of decay time, each channel individually and continuously adjustable
- Silent decay-time adjustments may be made during recording
- True stereo operation (separation ≥ 60 dB)
- Switchable to mono input
- Adjustable input sensitivity
- Built-in limiters (one per channel) to prevent overdriving of inputs
- No acoustic feedback… even when placed close to monitor loudspeaker
- Internally shock mounted against floor vibrations; no special mounting or isolation required for installation
- No periodic maintenance, adjustments or “tuning”
