The "difference tone" is a psychoacoustic phenomenon of an additional tone that is artificially perceived when two pure tones are sounding at the same time. Two real frequencies f1 and f2 can produce a virtual third tone fD, the difference tone which is kind of "unity frequency". The Deep Difference Unit produces 4 special difference tones developed for Korea: 4 states of a virtual, invisible unity of two different but close wave motions, an ambivalent unity of two different but closely related sides.
The loudspeaker sculpture reminds on the huge loudspeaker units installed by both states at the South/North Korean border to manipulate the other side with propaganda and music. But here they are standing extremely close together, producing a melody of difference tones, only audible for visitors in the zone in between. The deepest Korean difference tone produced in this constellation is the most ambivalent one, with 38Hz (which reminds on the cut at 38° after the Korean war), others seem to be more peaceful. Anyway, it's hard to hear - and may be not everyone can hear these "unification tones".

The loudspeaker sculpture is a small replication of the loudspeakers at the border, one representing the North and the other representing the South. The visitors can pass through - in real life that's not possible because the border zone is totally blocked on two kilometers on every side. In this real in-between-zone, the Demilitarized Zone (DMZ), nature resurrects to full life. Wild animals feel safe because man is not disturbing them: for humans it's a forbidden zone, for animals it's paradise - a touching contradiction in terms, depicting our human condition.
Thus, sometimes the voices of three birds out of that zone appear among the deep difference tones: the crane, the magpie and the golden oriol. For birds borders don't exist, and it is an old Korean song of the "Blue Bird" ("Saeya, saeya, parang saeya") which tells a sad story from the "Donghak Rebellion" in 1894 when the Korean people fighted against the own corrupt rulers and the growing Japanese dominance. The four tones of this melody appear transposed as deep different tone frequencies.
The Deep Difference Unit condenses different layers of the Korean history: the past, the present and - however - the future, producing a unique experience for every visitor passing through.