is it possible to stop loud sound waves from passing inbetween 2
points by using. eg a small square size wall without having anything
in there like glass. just air. i have already thought of a vacum but
that wont work cause its not stationary. then i thought of silent
sound waves that some how override the louder ones. but i also need to
know what type of thing can make this happen between 2 points?
eg.im stood in a room where someone else is on the other side. theres
nothing between us. can i stop him from talking to me so i can see him
talking but cant hear him. then if i step to his side of the room,
will be able to hear him.

Earmuffs are the most practical.

You are talking about 'counter balancing' soundwaves.

Answer is basically no, but a small yes. There have been many attempts
to cancel noise by detecting the sound and generating an anti-phase
signal to coincide at the listening point. Great in simple theory but
dumb in practice. Problems are manifest and it can only work at one
specific position because at all other places the sounds add. You
can?t ?cancel? sound, the energy is still there unless it is absorbed.

Moreover, a surprising amount of the sound comes from reflections, so
what ends up at someone?s ears is dynamic and under most conditions is
impossible to characterise. There?s also the problem of the microphone
(which detects the noise) picking up its own anti-phase signal and
howling.

Semi success has been achieved in airline aimed experiments whereby
cancellation takes place on the headrest at each side of the
passenger. Trouble is that it makes it even noisier for everyone else
and moving your head screws it up. The other big experiment was
undertaken for the military, attempting to reduce the cabin noise in
helicopters. They used multi-phase plates driven by simple transducers
and surprisingly (not at all!) the noise actually worsened. Any
competent engineer could have saved them a fortune by explaining basic
principals of superposition. These experiments gave rise to the new
crop of flat speakers, much vaunted and pretty useless. Doesn?t seem
to have been an impediment to sales though.

Only way that comes to mind is with a fast air stream -- *very* fast.
Bit impractical and in itself very noisy. Or you may have noticed the
sound deadening effect of heavy fog or a steamy bathroom. That?s an
illustration of absorption but not a lot of help either. If anything
else occurs to me I?ll add to this.

Best

lol earmuffs. just to clarify( wish i could draw a pic) imagine the
room cut in half by an invisable wave thats stoping all sound move to
the other side. so that if you stand on one side you can hear yourself
but cant hear your friend on the other, but if you cross over you can
hear him speakas he will you.  I know that there has been an
experiment done in a night club once where the people who sat in this
booth (that was open top aswell, not enclosed) could talk to each
other. but when they steped out they could hear all the load misic
that they couldnt inside. I seen this on i think tommorrows world ages
ago(long time, or maybe discovery channel lol, cant remember) it had
something to do with where this light was aimed. quite amazing but i
cant find anything on it or how it worked.
thanks

I think what you saw on ?Discovery? was a sound absorbent booth. This
harks to what I said about sound level being composed to a surprising
degree upon reflections. If you enter a semi-enclosed space with
highly absorbent walls, the sound level plummets. Anechoic chambers
are disturbingly weird to experience.

Best