[Anechoic]

and has been common(ish) knowledge among electrical engineers for decades.

Not only is it common knowledge it's how drive-thru kiosks work!

Source: I used to test microphone/speakers for a kiosk OEM.

[ycombinatrix]

Is it really a single unit that acts as both the speaker and mic? Can it do both simultaneously? Is that why it sounds so trash?