Should I use “speaker” or “loud speaker” to refer to the signal → vibration → sound thingy?

I am a native german speaker, so I have absolutely no good intuitions when it comes to choosing the right alternative out of a candidate set. Today, one problem was: How should I call the sound-making thingy? Is it a "speaker" or is it a "loud speaker"? Is there any difference?

• Is one term more technical than the other?
• Is one term stylistically marked in certain contexts? If so, which?
• Are there any useful, free, online resources that could help me answer similar questions in the future?
• Are there any objective criteria?

What I have come up with so far is: If I choose "loud speaker", I no longer might get the "person that is speaking" interpretation, but in the intended usage of the term (a manual for a technical device), such an interpretation should not arise anyways. So, it seems like an arbitrary choice to me.

Neither term is more technical. There are certain contexts where there is a difference between the two words. COCA is a good resource for answering such questions in the future. Yes there are objective criteria.

Generally speaking loudspeaker and speaker (in the context of a stereo system) are synonyms. However... I've heard many aficionados use the term loudspeaker pejoratively to indicate the sound quality isn't good enough for them.

The pejorative quality comes from the comparison to speakers used for public announcements. (ie a PA system) Speakers used in PA systems are loud, but otherwise not very good. A corpus search shows that loudspeaker almost always refers to sound systems used by activists, police, firefighters, stadium sports announcers, etc. They are used in public places both outdoors and indoors where loudness is more important that their dynamic range.

"Loudspeaker" (one word) seems a bit archaic to me. While not wrong, I feel like I would find it in the context of instructions for a "Hi-Fi system". But it is the name of the device.

"Loud speaker" (two words) implies a person who speaks loudly.

"Speaker" in a technical context seems clear enough. That's what I'd go with.