British Kinematography (1950)

78 BRITISH KINEMATOGRAPHY Vol. 16, No. 3 measure some particular physical effect, and it would require a host of meters to measure all the physical effects which go to make up a psychological effect — and then the answer would probably be wrong ! The term " reverberative effect " must not be, though it very often is, confused with reverberation time. Reverberation time is the time taken for a sound to die away, and the reverberative effect is the manner in which it does it. To take an example, consider a large room, the lower half of whose walls are covered with highly glazed tiles and the upper half with a six-inch layer of rock wool, which covering is also placed on the ceiling. If one were to enter such a room, the first sounds that would reach the ear would be the many sound reflections circulating in the lower half, whilst overhead would be fert a sort of oppressive heaviness. If now the treatment be reversed and the rock wool be situated in the lower half, and a heavy pile carpet be placed on the floor, whilst the upper half and the ceiling were tiled, then one would be greeted with a sombre heaviness on entering the room, accompanied by an overhead murmuring caused by such sounds that have escaped absorption in 0-0' NOI k l. THE OPTIMUM REVS "RE .RATION TIME' FALL £T WITHIN n i i kDllD AREA' 1 | r 1 1 1 -gr--... ' .2. E A»fi ( JN EATA Dili. TO R.watsi k — ni ^I»r? '/y^j 5 ^ *f? / i*'"^^ •>& f£4 T az & 2 &'<'■ I 10 ~** r?M — 4 [:::: Zj :;:. tftf ? & 5 * + + -* -J'-' 1 -- _j d bH t T f -< z J> -J iu-f< a. --o - rial 3 <S> $ ^ _ i ~. > — D 0 C — 3 _ in __ z Ul to » Ul CD 2 <J3 t 3 -J < ..._L 1 H 1000 lopoo ioqooo ipoqooo VOLUME OF STUDIO IN CUBIC FEET 10,000,000 Fig. 4. Optimum reverberation time as a function of studio volume. the lower half. In no way could it be said that the acoustics of the two rooms are the same, nevertheless, it is most probable that if the reverberation times of the two rooms were measured they would be substantially the same. Comparative Sound Treatment Such a difference was discovered in a pair of studios at the Maida Vale premises of the British Broadcasting Corporation, which were deliberately made of identical volume and of the same mean internal dimensions. The difference between them was that one of the studios had the walls and ceiling broken up with bold, zig-zag corrugations while the other had plane walls. The acoustical treatment consisted of covering substantially the whole of the wall surfaces with \ in. building board, and the floor with a carpet laid on building board over the concrete floor. The reverberation time of the two studios, when measured, was found to be substantially the same, but the reverberative effect was quite different, the studio with the broken up walls and ceiling appearing to the ear to be much less reverberant than that with the plain walls.