ONE of the great social inconveniences in present-day life for large numbers of people is the lack of quietness which modern building design and materials have brought in their wake. The problem is accentuated in the case of the many large blocks of flats and apartment houses which are being erected, all around us, whether for the well-to-do or for the slum dweller. The question of acoustic isolation for the occupants receives little or no attention in the majority of cases, and it is a common source of complaint that purely local noises can be heard throughout the length and breadth of large buildings constructed on modern lines. Yet architectural acoustics is no longer shrouded in mystery and empiricism, but is a science of which some of the physical prin ciples are well established, and the practical out comes are often predictable. A good deal can, in fact, be done to mitigate the noise nuisance in buildings. The policy of perfection is, of course, to stop or lessen the noise at its source, but this may often be quite unfeasible. Alternatively, we must erect some kind of sound-proof barrier, whether wall, window or floor, between ourselves and the noise.