jOrgan does not generate sounds itself, it delegates this part of an organ to sound devices. To be able to communicate these have to be controllable by way of Midi messages. Many sound devices are configurable with different samples.
See the following sections for possible types of sound devices that can be used with jOrgan.
Software sound generators can take advantage of the computing power and flexibility of a computer. A primary advantage is the high degree of polyphony that they offer, provided a sufficient fast computer is available:
Fluidsynth https://sourceforge.net/apps/trac/fluidsynth/ is one of the Software sound generator options. It is arguably the easiest way to hear sound from a jOrgan disposition, and while is a separate item of software, it can be chosen as an extension during installation, and appear to be a fully integrated function in jOrgan. Once installed as an extension and configured in a disposition it loads the .SF2 sample files on opening the disposition, and all its settings (including volume level and reverb parameters) are set as properties in the Element.
UVI is a free synthesizer (but not sound font player) http://www.uvisoundsource.com/uvi-workstation/article_info.php/articles_id/8
SampleTank is another free synthesizer(?)http://www.ikmultimedia.com/sampletankfree/features/
Pipes of real organs can be controlled by jOrgan too.
Different types of sound generators can be used together to benefit from all their advantages.