hi the question is about how can I arrange a microphone such that it has a "line of sight" kind of sensitivity, only in one direction? What Ive tried so far is to place a 5/8" dia tube towards the direction to be measured and the mic is at the other end of the tube. Ive found in listening to a running engine this helps to isolate where noise is coming from, but its not working for this. And Ive tried a "slit" where a 1/4" vertical slit is made in a wood panel, and this also did not give the selectivity needed. Im considering trying to take some home insulation material/fiberglass R13 and try to insulate everything but an opening. But wanted to ask, what are the physics involved? (I dont want to reinvent the wheel) I want the microphone response to be near zero except for the exact place its pointed at. the measurements will be taken in a straight line from 5 feet to 25 feet away from the microphone thanks!