Hi Adrian

I spoke to a friend yesterday and he said that beta brainwave stimulation is needed. I have just gone to the source of his information at http://www.comptronic.com/avestud5.htm

It says that in a study 12Hz(High Alpha) was used to stimulate the right hemisphere of the brain and 18hz(low beta) was used to stimulate the left hemisphere of the brain.
Inattention reduced to a normal score, and impulsiveness reduced to less than normal.

On Comptronic's website they state that their DAVID light & sound brainwave entrainment devices are ideal for ADD.

Hope this helps
Grant