A delay gap under 20 milliseconds makes a hall feel intimate

Evidence

In fact it seems that our preference is for a delay gap of less than 20 ms if the sound of the hall is to be classed as “intimate.” In sound reinforcement systems the output of the speakers will often be delayed with respect to their acoustic sound but, because of this effect, we perceive the sound as coming from the acoustic source, unless the level of sound from the speakers is very high. — David Howard, Jamie Angus, coustics and Psychoacoustics, 746