Except, "loud" is clearly an adjective, and using it to modify the verb "to speak" would be considered extremely low register. " It would not be used to request someone speaking in a normal voice to speak more loudly.
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AnonymousPlease speak loud/loudly/out loud/aloud, I can't hear you.Your sentence suggests to me that someone is already saying something out loud/aloud, but that the speaker's voice is not loud enough to hear properly.
AvangiIs this a recent development (i.e., in the last 60 years?)I have no idea, really, but it may simply amount to overdue acceptance of common usage. On the other hand, maybe we should look at it as being comparable to constructions using verbs of perception (?). E.g.:
KooyeenI say the music is loud, and the volume is high.Good idea. It seems, thank the gods, you're not one of those who talks about "prices being so expensive nowadays" or "the temperature being so hot"!