Assuming that your walls are 4m apart room will amplify 42.875Hz - (about the lowest sound of the bass guitar).
343/4/2=42.875
where 343m/s is the speed of the sound in dry air, 4m is the distance between the walls and 2 - because sound has to go forth (reflect from back wall) and back to add to sound produced by the speaker. There would be peaks and valleys at different distances, since it is standing wave, but you can play 40Hz and walk around. You can always attempt to decouple the speakers from the floor. I used Vibrapods directly under speaker, but it made my narrow speakers very unstable. You might want to use something like Vibrapods with large granit or marble plate and then speakers on the spikes. Vibrapods have weight rating, but there are many others similar. I placed pods with higher rating in the front (front of the speaker is heavier). It is easy to measure with weight scale. Vibration is also a function of speaker construction. My new speakers are standing on the spikes directly on the floor and I cannot feel or hear any floor vibration (basement underneath).
343/4/2=42.875
where 343m/s is the speed of the sound in dry air, 4m is the distance between the walls and 2 - because sound has to go forth (reflect from back wall) and back to add to sound produced by the speaker. There would be peaks and valleys at different distances, since it is standing wave, but you can play 40Hz and walk around. You can always attempt to decouple the speakers from the floor. I used Vibrapods directly under speaker, but it made my narrow speakers very unstable. You might want to use something like Vibrapods with large granit or marble plate and then speakers on the spikes. Vibrapods have weight rating, but there are many others similar. I placed pods with higher rating in the front (front of the speaker is heavier). It is easy to measure with weight scale. Vibration is also a function of speaker construction. My new speakers are standing on the spikes directly on the floor and I cannot feel or hear any floor vibration (basement underneath).