Moving into an apartment with wood joist floors - worried about neighbors hearing

The whole floor will act as a sounding board so it is necessary to damp the floor throughout much of the room, not just directly under the speaker.  Ideally you would get wall to wall carpeting with a very thick and dense pad.  If you can only manage area rugs, again, the thickest and densest rug covering as much as you can of the floor would help.  
 

The speakers should the be placed on vibration damping devices—specislty feet or s platform.  

It will become more a question of at what days and what time(s) of the day you do your listening.  Your choice of music will also figure into this.    

If you are listening at 2PM on a Wednesday, it is not going to matter all that much.  It gets much dicier in the evenings, late at night, and weekends, especially weekend mornings.

I was a coop board president for 14 years in Queens.  72 units; 6 floors.  It is a wooden floor affair.  You would swear that folks can hear mice whizzing on wool.  It's not just stereos that bother other tenants, it's all sorts of noise...  older refrigerators, large screen TVs, conversations, and (in neighborhoods with budding Asian child prodigies) pianos.  

Tenants are very very aware of everyone else's noise, but not their own.  Tenants can be unreasonable, uncaring jerks.  

Be reasonable, obey the building's ground rules, and you will be ok.  People LOVE to complain about EVERYTHING.  Just don't be a jerk and you will be ok.  

I would always inspect the noise complaints on my own and on my own time to determine the validity of the claim.  Most of the complaints were not justified.

As for myself, two systems ... one with floor standers, one with monitors.  The monitors are on top of bookcases, more for the cats than noise travel.  Carpets on the floor, drapes on the windows, equipment placement on the not shared walls ... that helps.  I don't play music very loud at all; above background levels, but below dancing levels.

Rich 

Nearfield listening for evenings, active XO and/or headphones, small maggies + sub

@hudsonhawk 

It would suck to have to get rid of speakers that you really like. One thing I would do is to introduce yourself to your neighbors and explain your passion for audio and your intention of not offending them with the sound. This might go a long way in trying to be a good neighbor!

Start shopping for headphones.