Sound

Description

Sound consists of pressure waves in the air, of which the intensity can be measured at different wavelengths or frequencies (number of cycles per second). The human ear is particularly sensitive to sounds with frequencies between 500 and 8,000 Hz, and furthermore responds in a non-linear manner.

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Frequency and noise level explained

 

Consequently, in order to measure the acoustic pressure level, reference is made to a logarithmic scale with the threshold of audibility as its origin.
The unit of measure is the decibel (dB).
The human ear also has varying degrees of sensitivity depending on frequencies.
 

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This is why, in order to judge the acoustic insulation performance of a material, we resort to weighting of acoustic levels in accordance with an ”A curve”.
Acoustics in buildings, however, take account only of the range from 100 to 5,000 Hz, which is split up into octave bands (frequency bands for which the upper limit is twice the lower limit) or 1/3 octave.

Sound dampening

Noise—unwanted, unpleasant, and disruptive sound—is increasingly present in our lives, affecting our comfort and even our health. Ordinary glazing is insufficient in blocking noise out. But today’s architects have ways to mitigate noise created by urban life: Saflex® Acoustic PVB interlayers. 

Used in a building’s façade (in standard windows, storefronts, and curtain walls), acoustic laminated glass provides significant sound transmittance damping—reducing noise from traffic, airplanes, trains, constructions, etc.  In interior applications, such as partitions and internal windows, acoustic laminated glass can help keep conversations private and create relaxing comfortable environments. 

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Mechanism of sound dampening
 

Saflex Acoustic glazing has sound damping capabilities and can, in the properly designed configuration, achieve a single number rating of 50 weighted reduction (Rw) or sound transmission class (STC) in comparison to ~30 Rw or STC for an insulating glass unit with 4 mm glass [12 mm air space] 4 mm glass. The use of high acoustic functioning laminated glass can help protect people from transmitted noise.

More than sound reduction glass, Saflex interlayers can also be designed to offer other benefits, such as, solar control, safety, security, and decoration. 

Many kinds of laminated glass can act as sound absorbing glass, thanks to the elastic behavior of the PVB between the glass panes. However, acoustic laminated glass composed of an acoustically engineered tri-layer PVB interlayer allows for greater reduction of sound.

When used in insulating glass units, the thickness of the different glass panes and of the spacer must be specifically designed to optimize performance.

 

Monolithic Glass

It is found that the glass panel is permeable to sound waves at the level of two frequency bands: below 250 Hz and between 1,000 and 3,150 Hz (depending on thickness). These two effects are caused respectively by the phenomenon of mechanical resonance, inherent in the glass, and the phenomenon of coincidence (frequency at which the glass panel begins to vibrate).

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(Source: conventional data of CEN (EN12758-1))

Sealed Unit (Insulated Glass Unit)

Resonance frequency in this case is inherent to the mass/air/mass system.
There is also the phenomenon of resonance of the cavity that separates the two glass panels. In fact, certain waves are reflected by both panels and thus cause the resonance of the cavity.
The frequency of coincidence is identical to that of the glass components.

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(Source: conventional data for CEN (EN12758-1))

Double Asymmetrical Glass Panel

An insulating panel with glass components of different thicknesses makes it possible to obtain greater performance, especially at high frequencies, because the coincidence thresholds of the two components are not at the same frequencies.
For an equivalent total thickness, a double asymmetrical glass panel has performance levels greater than those of a symmetrical double glass panel.

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(Source: conventional data for CEN (EN12758-1))

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