Can I suspend / hang speakers?

Non-rigid mount would be a bad idea, since the speakers would move in the opposite direction as the cones, according to Sir Issac Newton's First Law of Thermodynamics (at least I think it #1)- for each action there is an equal and opposite reaction. Only a little bit, but think how hard we try and make sure that speaker stands are rigid.

I did this in college when I lived in a storage room for a term (cheapest rent ever!) Hung 2 Boston Acoustics A60s from the rafters. Can't remember if they sounded good because I was drunk most the time. I doubt they did. There was a hardhat on the wall, in case anyone felt uncomfortable with it.

Yeah hanging from pipes mounted to the ceiling Joist would be sonically much better, all things considered(should strongly consider finding best sonic placement "in space first"). simply letting the speakers "hang" wouldn't sound so good, unless the speakers were "so heavy" they wouldn't react much to movement in the speaker.
I would "X" the hanging idea with chains, etc, yes. I mean, if the speaker is haning there anyway(obstructing walkways, etc), you might as well "hard mount" the suckers!

Someone has to say it...

It was Newton's THIRD law of MOTION
vs 1st of thermo.

"For every action, there is an equal and opposite reaction."

If I didn't think Newton was the greatest scientist ever I would have kept my mouth shut. Regardless of the historical slip you make an excellent point regarding the tendency of suspended speakers to shake themselves rather than produce sound.

Thank you Wade- Its been over 30 years since I studied any physics. I was just guessing on which law. I'll gladly take you word for it.