In the construction of a sound studio, a number of variables and conditions are involved that must be defined before starting any work. Surely, the application of the studio is the first to be defined and this is how there are sound studios for the production of master musicals, radio voice over booths, dubbing booths for television, voice over booths, television studios for drama, television studios with audience for musicals and contests, audio mixing booths, audiometry booths and other solutions that require special treatment.
Regardless of the conditions of physical location, size, budget, execution time, it is very important when talking about sound studies, to be very clear about two fundamental technical concepts such as sound insulation and acoustic adequacy. For those who are not familiar with acoustic technique there is a tendency to confuse and mix these concepts that are totally different and independent.
Sound insulation
If you build an acoustic enclosure it is because you want to obtain within it a sound of good quality, independent of external sounds that are not related to the main production. From the practical point of view, all the studios are located in an environment where there are sound sources generated by man and his work, such as airplanes, cars, voices, engines, office equipment, vibrations of work equipment in the streets, monitoring sounds of other studies, air conditioning systems, etc.; these, like all sound, propagate through a medium.
From this it is established that there are two fundamental ways of propagation: the first, through the air and the second, through the structures.
So far the only solution to block or attenuate the noise transmitted by the air is to interpose in its path high-density materials that prevent its passage, which is why the walls, floor and ceiling of sound studios must be built with very heavy materials such as solid bricks or concrete.
The level of sound insulation that is required may vary depending on the application of the study. For example, a higher level of attenuation is required in a drama studio than in a studio for competition with audience assistance.
Building these surfaces with solid materials does not entail a very high degree of difficulty, however, every sound study requires access doors, windows, in some cases, and air conditioning duct inlets and cable pipes, which goes directly against the insulation achieved with the dense materials used in the other surfaces. Therefore, maximum care must be taken in the design and construction stages of these elements.
In the case of doors, they must be built in solid wood and of a sufficient thickness that guarantees a good attenuation with high quality rubber packaging that can guarantee a hermetic closure. It should not be forgotten that the door frames should be attached to the wall without allowing any hole or slit that facilitates the passage of sound. It is common practice to seal these expansions with silicone or other similar material. In the case of windows, the frames should be made of a solid material, with non-parallel glass sitting on neoprene packaging.
The air conditioning ducts, both injection and return, are an expedited way for the entry of noise into the study, therefore the use of high attenuation sound traps and silent air conditioning units is suggested. The gaps made for the passage of pipes must be sealed, after the installation of the cables, with acoustic materials such as tow, fiberglass or polyurethane foam.
Achieving isolation from airborne noise is relatively simple compared to the task of preventing noise transmitted by the structure from entering the study. To understand this phenomenon, it is enough to remember that if a person brings his ear to a railway rail, he can hear the vibrations of a train that is miles away without hearing the noise of it traveling through the air.
Similarly, a sound studio that is located within the structure of a building, is affected by the knocking of a hammer, a compressor or any other element that makes contact with the structure of the construction, the sound will travel through the concrete and iron elements that are in the structure to the walls of the studio, regardless of whether the latter are thick or not, leaving as a result an unwanted noise inside it.
The only solution to avoid these noises that travel through the structures is to physically isolate the walls, floor and ceiling of the studio, from the rest of the structures of the building. This technique is known as "box into box". From a practical point of view, achieving this structural independence is complicated and costly, especially when it comes to large studies.
In the case of a voice over cabin it is relatively simple to melt a concrete plate on an insulating base of neoprene, cork or other insulating material and, on this small plate, raise the internal walls, on which the roof of the cabin will be supported to form the structurally insulated box.
When the studio acquires larger dimensions, the foundations that support the walls of the internal box must be different from those that support the external box. This is a more complex work that is justified depending on the site where the study is located and the quality of insulation required.
A common practice that causes many problems is the installation of air conditioning systems on structures (ceilings) that are part of the structure of the sound studio.
When building a sound studio with the box-in-box technique, extreme care must be taken not to lose insulation by metal pipes or air conditioning ducts that can acoustically short-circuit the structural insulation. In other words, there must be no rigid element common to internal and external structures.
Acoustic adequacy
Once the sound studio is isolated from external noises it is necessary to adapt it internally so that the sounds produced within it respond to the application for which it was built. This has to do with two fundamental variables that are attenuation and frequency, whose interrelation gives us as a result the reverberation time characteristic of the study.
It is important to understand that within the study the sounds propagate through the air, are attenuated and reflected in greater or lesser quantity, depending on the material with which the internal surfaces are covered and the frequency of the sound produced.
In general terms, if the internal surfaces are hard, the sound will be reflected in greater quantity producing an echo phenomenon; if the surfaces are very soft, the sound will be absorbed, producing a "dry" sound effect. This causes the study to respond with very low levels of reverberation, approaching level zero, which is commonly referred to as a "dead" study.
The combination of hard and soft materials, the location of these and the dimensions of the studio will produce a response to sound that is particular to each studio, so it is said that a studio is more or less "bright" or that it is more or less "opaque", which generates, subjectively, a preference to make recordings in certain studios.
In a television studio for drama, the simplest thing is to build it very "opaque" because there is the electronic resource in post-production to add reverb effects, equalization, etc. In a chamber music auditorium, a high acoustic compromise must be achieved between reflections and attenuations so as not to distort the natural sound of the instruments and, that is why, there are usually walls and ceilings covered in wood that allow the reflection of high frequencies, which are the most easily attenuated on soft materials.
As can be seen, the internal adequacy of the study is closely linked to the specific application of it and due to its complexity, it is a practice of approximation, through its construction, to a hypothetical response curve required by the design. Of course, the calculations of the acoustic engineer will allow a more accurate approximation.
Leave your comment