Why AM radio receivers need more than an antenna and speaker?

[Asymptotic]

From what I'd been reading, Reginald Fessenden devised the first audio detector circa 1902. As @sophiecentaur said, coherers and Marconi's magnetic detector aren't rectifiers, and are incapable of demodulation.
https://en.wikipedia.org/wiki/Electrolytic_detector

 

[marcusl]

Read the first paragraph in your link:
"It was one of the first rectifying detectors, able to receive AM (sound) transmissions. "

 

[Asymptotic]

Read the first paragraph in your link:
"It was one of the first rectifying detectors, able to receive AM (sound) transmissions. "

Perhaps I phrased it inelegantly. Giving it another go ...

Neither coherer nor Marconi's magnetic detector can demodulate audio. This milestone wasn't achieved until 1902 when Reginald Fessenden devised the electrolytic detector.

 

[marcusl]

Got it! Thanks for the clarification.