John Gill Commentary Acts 19:34

"But when they perceived that he was a Jew, all with one voice about the space of two hours cried out, Great is Diana of the Ephesians." — Acts 19:34 (ASV)

But when they knew that he was a Jew
And so equally an enemy to their idolatry, as Paul and his companions were, whether he was a Christian or not.

All with one voice about the space of two hours cried out ;
all that were in the theatre lift up their voices at once to prevent Alexander's apology, or at least its being heard; and which they continued about two hours, which was a long time to keep hallooing out,

great is Diana of the Ephesians; (See Gill on Acts 19:28).