Storage of other speakers in the room, shorting them while not in use? Myth or true?

There is absolutly no question that all other speakers in the room should be "shorted" to limit bass absorbing cone movement. I built over 200 HiFi stores with high end soundrooms  during my 40 year carrer in HiFi. When we designed and implimented a "shorting" speaker switching system, the measurable and audiable improvement was simply amazing. Now, having one or two pairs of "unshorted" speakers in the same room might not have the same effect as twenty or thirty pairs....but it can't hurt to just make up a couple short cables to short out your speakers in waiting.

I can’t say that I have first hand knowledge of cones moving when other speakers are playing.  But, I can say that I’ve noticed that my wife’s lips start moving when she objects to the music I am playing.

Given how many discussions on the forum deteriorate and get testy, this one had been very entertaining and fun to read thanks...!

You don't want anything passively vibrating in response to music signals, whether that's musical instruments or unconnnected speakers. If other speakers have to be in the room, the simplest thing is just to put them face down on the floor or put them with the drive units face to face and off axis to the main speakers.

On the subject of a speaker being a microphone in reverse, lots of studios have Yamaha NS10 or similar woofers converted to act a kickdrum mics.

Wow, this is news to me!