Set [source.loopEnd] to value.
Often I open the Docs to look for some explanations I stumble into things which must be researched.
What does value in this case mean? seconds? milliseconds? percent? bytes 
? beats 
?
Wouldnât it be better to explain what is meant without further research? 
While I completely agree that the docs often state things assuming previous knowledge of the topic, in this case, simply clicking on the link from the explanation opens this MDN link which states:
The
loopEndproperty of theAudioBufferSourceNodeinterface specifies is a floating point number specifying, in secondsâŚ
so not much âresearchâ needed in this case to find out the answer to your question.
Other than that, while Three.js often require too much research on various stuff that are not so easy to wrap your mind around, a light or moderate research on some topic is always needed to properly understand how it works. Personally, I believe that always serving things on a plate is, generally speaking, for lazy people or those that spend too much time on their smartphones and canât read too much or solve a mystery by themselves anymore, really.
How you make the truth 3D like that? That from THREE.TruthRenderer? 