340 Recording Studio Design 12.5 A BBC solution Large broadcasting organisations such as the British Broadcasting Corporation (BBC) may need to transfer programme material between many studios in many different locations. Staff may also frequently move between studios, and to work efficiently they need to be able to settle quickly into an unfamil- iar room with a minimum of time for acclimatisation. They need to work rapidly and reliably, and to feel confident that the ensuing broadcasts are well balanced in people's homes. There is also a tendency for the broadcast indus- try to rely on free-standing loudspeakers, with all the attendant problems of edge diffractions, the confusion caused by rear radiation, and the response variability with respect to position. Broadcasting staff often have their own ways of working, which necessarily differ from the music recording industry, and any new rooms that are introduced into a studio complex usually need to be closely compatible with existing rooms. The deader acoustics of many music industry control rooms are gen- erally not well liked in the broadcast world. The tendency is still to favour rooms with characteristics not unlike the IEC rooms, but this type of construc- tion is not always appropriate because of limitations on size. In 1994, Bob Walker presented a paper 5 on a newly developed type of room for the BBC, which was to exhibit a relatively uniform decay time with frequency. It had the added specification that no reflexions should arrive at the ear within 15ms of the direct signal, and that no reflexions arriving after that time should be more than -15 dB relative to the direct signal. The concept is shown in Figure 12.5. The ceiling, as can be seen, is of generally similar shape to the walls, which seems logical considering the three-dimensional expan- sion of the sound waves. The floor dip problem, discussed in Chapter 11, is partially blocked by the siting of a mixing console between the loudspeakers and the listener. The design concept relies on the positioning of reflective surfaces in such locations that they will not reflect energy from the loudspeakers directly towards the listener, which is not as easy as it may seem. In reality, unlike the images shown on computer ray-tracing programs, the sound waves do not travel in straight lines according to Euclidian geometry. They travel as expand- ing waves that are greatly influenced by diffraction effects at most audio frequencies. The diffraction ensures that non-specular (i.e. unlike light) reflexions will travel in unpredicted directions, only to be re-diffracted from other boundary discontinuities. The design of such rooms is therefore not a simple matter. Nevertheless, the above concept has much to offer in some difficult circumstances, and its concepts are valuable when free-standing loudspeakers must be used. 12.6 On listening rooms in general When rooms are to be used for listening to music for serious enjoyment, almost all of the concepts discussed so far in this chapter must be taken into account. Simply placing loudspeakers in any convenient location will not suffice. It must be understood that in a highly reverberant room, with little furniture