140 Recording Studio Design further, but in the neutral type of room under discussion here, whatever reflexions exist should tend to be reasonably well scattered, otherwise they will develop a character of their own and the room would lose its neutrality. 5.6 Floor and ceiling considerations Let us now look at possible ceiling structures for our neutral room. As we discussed earlier, the nature of the floor has been chosen to be wood. Carpet tends to produce a lifeless acoustic, uninspiring for the musicians and unhelpful for the recordings. Stone was rejected, partly for its `harder', more strident reflective tendency, but also on the practical ground of slippage. Floors of neutral rooms overwhelmingly tend to be of wood. At this point of the design stage (see Figure 5.3), we have a relatively dead ceiling at a height of about 4.5m. We cannot come down too much below this because the reflexions which we would introduce would tend to become of the tone colouring, early nature. What is more, too low a ceiling would preclude the siting of microphones above the instruments at a height which may be necessary to cover any given section of musicians. One solution to such a problem is to construct a ceiling of wooden strips, with spaces between them which would allow a good proportion of the lower frequencies to pass into the absorbers behind. They would therefore provide mid and high frequency reflexions without allowing an unwanted low frequency build-up. As mentioned earlier, in order to reflect at low frequencies, surfaces need to be of sizes comparable to the wavelengths to be reflected. We can therefore have some degree of control over the lower limit of our desired reflectivity by providing gaps in our reflective surfaces at appropriately chosen intervals. This alternative juxtaposition of reflective and absorbent surfaces will also produce significant diffusion (see Section 4.7), which in many instances is extremely useful. Once again with this complex subject there are so many ways of achieving each objective, so here we will only be able to look at some of the possibil- ities within one technique of specific interest. The strips described could be of hardwood or softwood, and could be plain, varnished, painted, rough or smooth. Each will give its own subtle character to the sound. Hardwoods, untreated, can be quite interesting sounding, but in today's ecological climate many designers refuse to specify any woods of an exotic or not too easily replenishable nature. Sound is of course important, but there are also environ- mental considerations which we cannot escape. Obviously, we do not want to encourage the build-up of resonant energy in any modes which would unpleasantly colour the sound, so the ceiling surface can be broken into a series of angled sections, set to produce what the designer would consider to be the most appropriate angle for reflexions. A selection of possibilities for ceiling designs are shown in Figure 5.14. Figure 4.33 showed a pattern of wood/space ratios which are based on a numerical sequence, not dissimilar to the one used for the diffuser cavities referred to earlier. This type of arrangement could also be used, though perhaps it would be a little tricky to find a suitably attractive way of mounting the lights. The purpose of all these arrangements, however, is to help to prevent any noticeable patterns forming in the reflected sound-field.