The formation of echoes can take place when the reflecting surfaces are located at a distance greater than ______

Clean air should contain less than ______ of suspended impurity per cubic metre.

In ___________ process, the fresh air is forced in the room and the vitiated air is allowed to leave the room by itself …

The value of __________ depends on type of activity, geographical conditions, age of occupants, etc.

The defect of _______ results in confusion with the sound created next.

Because of high concentration of reflected sound at the Sound foci, there is a deficiency of reflected sound at some poi…

The general temperature difference between inside and outside of a room is not more than ________

In Winter, the outside air is cool and hence, the process of air conditioning involves filtering, preheating and _______…