What is the minimum distant for Zu?

Zu has said in the past that Def models with rear-firing sub-bass arrays can be used as close as 2" from the wall behind them. And it's true. Is that ideal? Depends on your room and how much flexibility you have for placement.

What's more important with Definitions is making sure the distance between you, the listener, and the speakers is usable. Def 1.5 and Def2 did not soundstage nor tonally integrate well if the listener sat closer than 10' from the speakers. Sean Casey told me that Def3 and 4 are usable as close as 8' from the listener. While I suggest more, I have to say the deleterious effects of sitting too close to Def 4s are much less troublesome to illusion of fidelity than doing same with Def2 or earlier.

The rear-firing sub drivers are active below 40Hz unless you set the EQ to roll them I higher. Don't. Let your Def3s end up as close to the wall behind them as is necessary for you to achieve full tonal and spatial integration at an appropriate distance listening. Prioritizing distance to the wall over correct minimum listening distance will make deny you the speaker's full benefits. Work with your room.

Phil

The right distance is highly room-dependent. But you have lots of latitude for the minimum acceptable distance. The original Definition architecture with the rear-firing sub-bass array can be used as close as 2" from the wall behind them. Side walls and other boundaries will affect your perception of the soundstaging but sometimes you just don't have a practical choice. 2' from side walls is certainly within guidelines for acceptable placement.

Depending on the room, experimentation may lead to widely differing conclusions. You might trade image scale for lessened constraining effects of side walls. But you might make it up with less toe-in. Def3s have the nano FRDs, so you get more spatial latitude to dial in your preference on the continuum from precision to sheer spatial scale. Get away from booming effects of corners if possible and then prioritize soundstaging.

Phil