The output energy control is developed for 1-D string model with fixed endpoints. It is considered a practical situation where a finite number of spatially-sampled sensing and actuation are available. First, the speed-gradient method is generalized in the present framework to pump/dissipate the energy of underlying model to a desired level provided the state feedback is available. Next, Luenberger-type observers are additionally developed over collocated position and/or velocity measurements to be involved into the output feedback synthesis. Capabilities of the proposed synthesis and its robustness features are illustrated in numerical simulations.