It uses an air bubble curtain to contain a sound signal which is generated pneumatically. Effectively, this creates a "wall of sound" (an evanescent sound field) field that can be used to guide fish around river structures by deflection into fish passes.

Physically, the BAFF comprises a pneumatic sound transducer coupled to a bubble-sheet generator, causing sound wave to propagate within the rising curtain of bubbles. The sound is contained within the bubble curtain as a result of refraction, since the velocity of sound in a bubble-water mixture differs from that in either water or air alone. The sound level inside the bubble curtain may be as high as 170 dB re 1mPa, typically decaying to 5% of this value within 0.5-1 m from the bubble sheet. It can be deployed in much the same way as a standard bubble curtain, but its effectiveness as a fish barrier is greatly enhanced by the addition of a repellent sound signal. The characteristics of the sound signals are similar to those used in SPA systems, i.e. within the 20-500 Hz frequency range and using frequency or amplitude sweeps.

FGS acoustic BAFF systems comprise the following components:

BAFF Unit
The BAFF system comprises of modular sections, each 2.4 m long, which are linked together to form the required length. The acoustic signal is entrapped in the bubbles by a driver unit and the resulting 'wall of sound' produces an uninterrupted guidance system.

Air Blower or Compressor
The BAFF uses an air blower or compressor to supply pressurised air to create a continuous bubble curtain.

Air Blower / Compressor Pipe
A temperature / pressure resistant pipe delivers air from the air blower or compressor to the BAFF control equipment.

BAFF Control Equipment and Control Lines
The BAFF control equipment is used to operate the BAFF system. A main air supply and two control lines feed driver units fitted on each of the BAFF units. Solenoids located in the returning control line regulate the airflow to the driver units. Pressure feedback lines run from the BAFF units back to the control panel to allow pressure within the BAFF to be monitored. An alarm system indicates a sudden drop in pressure resulting from a failure in air supply.