If the direction of the wind is at 45° to one of the faces, negative pressure will be produced on ______

The branch of science which deals with origin and propagation of sound is called as _______

For lecture halls, large volumes are beneficial for weak sounds.

If the direction of the wind is at 90° to one of the faces, positive pressure will be produced on ______

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

The rate of flow of air arising due to the difference in temperature of outside and inside is given by the expression __…

_______________ system is just the reverse of the exhaust system.

The average height for small halls should be _____