Ergo
headphones look more like a helmet than like conventional headphones
and are quite inflexible for different head sizes etc.
In Germany Ergo headphones are distributed by Quad. This is the
reason why you see a Quad speaker in the background.
This
Year Ergo introduced a new
type of headphone based on an air motion transformer with an impedance
of 4 Ohms which has to be connected to a real power amplifier.In
the data sheet the sensitivity of that headphone is not given..