Learn About Soundproofing
General Definitions
Hertz – Hertz (Hz) is a unit of frequency. One Hertz is defined as one cycle per second. The human ear can hear up to 20,000 Hz. Below 20 Hz, sound is no longer perceived as a musical tone but as a rhythm. The lowest note on a standard piano is an A at 27.5 Hz. The lowest note on a guitar is an E at 82 Hz. Middle C is about 262 Hz. The highest note on a standard piano is a C at 4186 Hz.
STC – STC stands for Sound Transmission Class and is the reduction in dB a partition can provide over a range of frequencies. It is a rating of how well a building partition isolates airborne sound. The number is derived from sound attenuation at specified test frequencies. It is used for interior walls, ceilings, and floors. The effectiveness of various partitions can be ranked on the basis of this measurement, which uses the transmission loss of sound in the frequency range 125 to 4000 Hertz. That said, the STC is weighted more heavily for attenuation around the frequencies of human speech and is not a reliable estimate for the attenuation of low frequency sound.
Transmission Loss – Transmission Loss is a measurement of the reduction in dB that a partition provides at any given frequency. For instance, if an 80dB sound at 50 Hertz is reduced to 50dB by a wall, that partition is said to have a transmission loss of 30.
Solution Postulates for Effective Soundproofing
Creation of a Cavity Space – When attempting to increase the STC value of a window construction, the most effective method is to create cavity space between two layers of glass. Noise from the exterior environment causes the outside windowpane to vibrate. As the glass oscillates in and out, it compresses the mass of air trapped in the cavity space. The greater the volume of air in the cavity space, the greater the mass. The inertia of the air trapped in this cavity space, resists the increase in pressure instigated by the vibrating glass. This damping effect attenuates the noise entering from outside.
Addition of Mass – The addition of mass as a barrier is an effective way to attenuate airborne noise. A good rule of thumb is to estimate that for a given frequency, each doubling of surface mass will result in about 6 dB reduction in sound levels. Because the math involved is rather tricky, we model our construction methods with acoustical prediction software to determine the Sound Transmission Class of our constructions.
De-Coupling of Adjacent Surfaces – Structural borne noise occurs when the components of the wall, floor or other building elements are set into vibratory motion by direct contact with vibrating sources. These sources can be airborne noise as well as mechanical equipment or domestic appliances. This mechanical energy is transmitted throughout the building structure to other wall and floor assemblies with large surface areas, which in turn are forced into vibration. These vibrating surfaces, which behave like the body of an acoustic guitar, transmit their motion to the surrounding air, causing pressure fluctuations that are propagated as airborne noise into adjacent areas. By de-coupling adjacent surfaces through various materials such as resilient channels, sound clips, and acoustical caulk, we stop vibration from propagating through a structure.
Cascading Densities of Materials – A trade secret. But if you ask us nicely, we will explain it to you in person.
Tightness of Fit – A great acoustical design can be foiled by noise leaks. If a door or window, for instance, is improperly installed, air gaps can allow the direct transmission of sound around the high-tech barrier. A design is only as good as its weakest link. Therefore, it is imperative that soundproofing materials are only installed by licensed acoustical contractors. Furthermore, it is essential that your contractor has experience with all aspects of the noise control field. Certain factors can often work at odds with each other. For instance, tightness of fit is essential to eliminate noise leaks. Yet, window frames affixed rigidly to a wall will propagate vibration through the adjacent structure. Therefore, acoustical contractors must be adept at guaranteeing a tightness of fit while providing resiliency between the building components.
Vibration Damping – Vibration Damping refers to the technique and the category of materials, which reduce vibrational noise at the source. A structure emits noise when it is excited by forced vibration. This forced vibration can stimulate the resonant frequencies of the structure amplifying the amount of noise. An example of a resonant vibration is the sound that occurs when one strikes a gong. A large amount of this noise can be reduced by converting this acoustical energy into heat. This is achieved through combinations of a variety of materials and techniques tailored to each unique situation. Some examples of machinery we commonly treat are hot tubs, air conditioning units, computers, air compressors, elevators and garbage chutes.
