266 Recording Studio Design 9.5.3 Balanced power In some hostile power line environments, one of the best solutions to avoid interference problems coming in via the electricity supply can be to balance the power. This involves the use of power transformers with centre-tapped secondary windings, producing, for example, 115 V-0-115 V in place of a single 230 V supply. Electricians should be consulted if this sort of measure is needed, in order to avoid making any illegal installations, but the technique can reject interference in exactly the same way that balanced audio lines are less sensitive to interference than unbalanced lines. Signal-to-noise ratio improvements of 15­20 dB have been reported as a result of power balancing. In many countries, it may be illegal to supply balanced power to normal wall-socket power outlets. Special installation work may be required, by expert engineers. Many electricians may simply refuse to do it, as they cannot justi- fiably put their signature to something with which they are not familiar. Never- theless, specialist engineers can usually find legal ways of installing such systems if there appears to be no other option for interference suppression. It should also be stressed that with such a specialist job as studio electrics, it is all really a job for electricians with some experience in this field if the highest standards of performance are required. 9.5.4 Mains feeds