Cut an Ikea table leg to desired length and mount upside-down and screwed into the desk top.

This printed part fits the right amount of snugly into the leg tube and makes for a solid mount for a desktop speaker stand.  Route the speaker wire through the rear hole for some measure of security (example: standing desk, in case wire gets pulled when raising desk, to avoid pulling the speaker off the stand)

I made this for the Polk RM2350 speakers, but any similar small size will work.

I rely on some ¼ foam with adhesive backing on the speaker bottom for vibration isolation and anti-slip.