OTTOsonics is a collective project by sound artists, developers, scholars and sound engineers working on accessible audio technologies for immersive sound production. Putting the focus on the needs of artists as well as non-specialized cultural and educational institutions, our objective is facilitating the use of immersive audio. In this workshop we will introduce and discuss our methods towards designing, building and maintaining an accessible high-density array of 3D-printed loudspeakers (100 speakers or more). For instance, how to 3D-print your own good quality speakers and design custom audio amplifiers, or how to adopt open source and open hardware standards. Finally, we will elaborate on how to test and evaluate the quality and usability of these systems.