What is Noise?

Noise is unwanted sound, but in a recording studio or in any audio room, noise can cause a lot of problems. Low noise standards are necessary with the recording studio environment, because equipment can pick up any unwanted noise produced.
Often the greatest noise to which audio/recording rooms are exposed is the noise from within the building. Noise comes from sources such as lighting, heating, ventilation, equipment used within the studio, mains hum, etc. The other source of noise is the general environment around us, for example, airplanes passing overhead, traffic, emergency services sirens, barking dogs, automobiles… The only protection from such noise is that offered by the walls, floors and ceiling of the building.
There are two ways in which sound can be heard: either airborne or impact. It depends upon the person who can hear the sound as to which category it falls into. For example, footsteps would be heard as airborne if the listener is in the same room. If the listener is in the room below, it would be heard as an impact sound. The reason for having to differentiate between the two types of sound is due to different methods of reducing the sound and different types of insulation specific to eliminating certain types of sound.
Some methods of preventing noise are discussed below. Prevention methods used to stop unwanted noise may seem costly at first, but the effects of unwanted noise in a recording environment, for example, are devastating.
Sound Absorption
Sound absorption is a reduction in the sound energy reflected from a surface.
Sound absorption is a major factor in producing good room acoustics, especially when controlling reveb. Sound may be reflected, refracted, diverged and diffused. The only way to get rid of it is to change the acoustical energy to another form.
This is the most commonly available type of noise absorber. These absorbers are fuzzy, fibrous vegetable or mineral materials, i.e. foams, fabrics, carpets, soft plaster, acoustical tiles, etc. The sound wave causes the air particles to vibrate in the porous material, and the friction causes some of the sound energy to be converted into heat energy, therefore reducing the noise heard. This is more efficient when working with high frequencies.
Low frequency absorption is attained by using thicker material. The thicker the material the greater the absorption. It is important to note that the correct density of the material used be maintained. If the material is packed too loosely, then not enough sound will be absorbed. If the material is too tightly packed, then the sound may be reflected off the surface and once again there will be no absorption.
Tiles, Panels and Foams
Acoustical tiles and panels are also widely used to “condition” sound. They are frequently used in constructing suspended ceilings. These tiles are relatively soft fibrous boards. They are often treated as “sound deadening” panels in studio treatment. They are often mounted behind or between Gypsum board layers and offer a method of providing some damping effect.
Walls for studios and audio rooms are subject to transmitting noise unless treated. The bigger the wall and the more damped it is the smaller the problems introduced by diaphragmatic resonance.
If a studio is being built inside an existing building it requires careful attention to the floor. If the studio is on the ground floor of a frame building, the floor is the only barrier between the low noise room and the environmental airborne noise penetrating the underside of the floor. If the studio is being build in an upper level of an existing building, its floor will be the ceiling structure of the room below. If the studio is built within a steel frame building with concrete floors, this causes its own set of problems.