SILENCE AND PEACE
Several studies conclude that noise can affect physically and psychologically the human being, compromising the quality of life, which is defined as the “individual perception about his/her position in life, in cultural and system of values context in which he/she lives, and concerning his/her main goals, expectations, patterns and worries” (Occupational Safety and Health Administration, 1998).
Windows and doors are often one of the weak points and when it comes to solve the problem, there are several issues we must take into account. One of these is the glass which is going to be used, as it is a strong ally in solving sound problems.
The noise, frequency and sound level
Noise is defined as any variation of the atmospheric pressure detected by a human ear, whether it is in the air, water or in any other propagation way.
Noise presents itself in three main characteristics: the timber allows us to distinguish, for example, the same musical note emitted by different musical instruments, the frequency related to the number of vibrations per second is the Hertz measure (1 Hertz= 1 vibration per second), the higher the tone is the higher is the number of vibrations per second and the sound Level is the difference of the wave pressure. In a logarithmic scale it is expressed in decibels, dB.
Human ear picks up noises over 20dB, over 140 dB can cause pain and over 175 dB the hearing is destructed.
Decibels in practice
When we calculate decibels, 1+1 isn’t equals to 2. Two 50 dB sources aren’t 100dB but 52 dB. When doubling the noise source there is only a 3 dB increase. To increase in 10 dB the sound sources it would have to be multiplied by 10.
We must take into account that even a difference of 3 dB in insulation between products is equivalent to a 50% reduction in a sound intensity; our ear doesn’t notice these changes in a sound level in a linear manner. This means that a sound insulation improvement of:
- 1 dB is almost unnoticeable
- 3 dB is noticedl
- 5 dB is a considerable change
- 10 dB reduces the noise to half.
Sound perception and the insulation value
Not all frequencies are heard with the same intensity by human ear, although possessing a sound pressure with the same magnitude. Human ear realises that a 100 Hertz sound is weaker than a 1000 Hertz sound, though the level is the same.
This ear sensitivity is very important when it comes to evaluate sound problems by correcting sound level (in dB) in accordance with the standardised curvature.
Sound insulation spectrum provides all data concerning glass sound performances, however, it isn’t an instrument easy to read, and thus it is normal to present these values from a graphic image of a coefficient series which “summarise” the sound insulation spectrum. Today and according to EN ISO 717-1 standard, we find a standardized value that includes 3 terms which simplify an easier analysis, Rw (C:Ctr).
Global insulation value (Rw) refers to an average between insulation in all frequencies, also called “Weighted sound absorption coefficient”.
C terminology refers to the value of pink noise spectrum adaptation (shrill sounds). For example: fast road traffic >80 Km/h, fast road traffic, proximity to airplanes, daily activities (words, radio, TV set, music, children playing).
Ctr terminology refers to the value of standardized traffic noises spectrum adaptation (low sounds). For example: urban traffic, disco music, low road traffic, railway terminals, airplanes at long distance, helicopters.
Sound insulation
Sound insulation depends on several parameters:
- Mass law: the thicker the glass is, the bigger is the insulation.
- Thickness difference between the glasses: the fact that the noises passes through the glasses of different thickness causes bigger noise insulation.
- Laminated glass: the use of a normal pvb increases sound insulation very little (1 dB) and although the laminated has more than a normal pvb, sound insulation doesn’t improve. However, with a AKUSTEX® pvb, sound insulation is noticeable, since the improvement between a normal pvb and a AKUSTEX® one is of 3 dB or more.
- Chamber: the bigger the chamber is, the bigger is sound insulation, although this increase isn’t that noticeable
Sound insulation doesn’t only depends on the glass, or depends only on the glass, but also a great important part of the insulation will depend on the whole window frame, as well as it correct installation.
