It is well-know that spatial impression is one of the important characteristics in concert halls. It is popular belief that early sound contribute to apparent source width (ASW) and late sound contribute to listener envelopment (LEV). The major concern of our study originated from the question of whether or not ASW was created only by early lateral sound energy alone. In this paper, a group of psychological experiments are performed with simulated sound fields. In the experiment, listening tests were carried out in order to exam the effect of early lateral sound energy fraction(LFE) and early to late sound energy ratio (C80) on perceived ASW. The results confirmed that C80 affects ASW.