60 Recording Studio Design At the other extreme, let us consider the isolation needs for a recording studio for orchestral and choral use, sited in an office building in a location above an underground railway and surrounded by streets with heavy traffic. In this case, it would be unacceptably expensive for noise-induced delays to affect the recording of a 100-piece orchestra due to underground train rumble during quiet passages. It would also be unacceptable for the fortissimo pas- sages to disturb people who may be concentrating on their work in adjacent offices. The isolation work may require the construction of an entirely floated inner isolation shell, of considerable weight, which may need the reinforce- ment of the floor in order to support it. In turn, this new hermetically sealed box would need to be penetrated by HVAC (heating, ventilation and air- conditioning) systems, which themselves would require considerable isolation. The costs could be very high indeed. In the first of the cases discussed above (the studio for the synthesiser band), probably the only acoustic recordings would be of close-mic'd vocals and the occasional guest musician. Neither the sound egress nor ingress would be particularly problematical, because there would be nobody to annoy by any external leakage of the sound, and except for the rare coincidences of extreme weather conditions during the recording of an even rarer acoustic guitar, the signal to noise ratio of recordings would generally be excellent. The only problem in this type of situation is that it would be restricted in its use. To some degree, though, all recording studios are restricted in their use; none are universal in their applications. In the second case, after due isolation work and internal acoustic treatment, the studio would be capable of recording just about any type of music at any time of day. The main restriction would be financial. After spending so much money on the studio building and preparation, the hourly rate would need to be prohibitively high for the general overdubbing of vocals, for example. That high hourly rate may be inconsequential though, compared to the cost of an orchestra's expenses when travelling to a studio in a distant out of town location. It is true, therefore, that an isolated location, by virtue of its distance from noise related problems is an option for reducing isolation costs, because the physical, geographical isolation is acoustic isolation. However, when overall convenience of access is important, this geographical isolation may be com- pletely impractical, so the only solution may lie in the choice of an inner-city site and a considerable amount of acoustic engineering. 3.10 Discussion and analysis Clearly, isolation is not a simple subject to grasp, and no simple computer pro- grams can solve the problems. Isolation is a subject for specialists, and where critical situations exist, the cost of calling in a specialist before construction will surely be less than the cost of trying to fix the problems after construc- tion. In fact, the problems may lie deep within the construction, in which case total rebuilding may be required. Intuitively, leaving out a layer of fibrous material between two of many layers in an isolation system may seem insig- nificant, but if the cavity resonates without the lining, the air at resonance can be a remarkably strong coupling medium.