The sound insulation performance of glass is measured by the weighted sound insulation Rw or the sound transmission level STC (Sound Transmission Class), and the unit is the decibel (dB). Chinese standards use Rw, and European and American standards mostly use STC. The values of these two parameters are slightly different. The STC value of the same glass is equal to or slightly lower than Rw, that is, it is more difficult to increase the STC value. To analyze the sound insulation of glass, it is necessary to understand the law of compliance of the sound insulation performance of glass, the relationship between the subjective perception of sound by the human ear and the weighted sound insulation, and then rationally configure the glass structure to obtain the best sound insulation effect.
The Human Ear's Perception of Sound
The frequency range of human ear perception of sound waves is between 20 and 16000 Hz. The subjective perception of sound is related to the weighted sound insulation value as follows:
The sound insulation is increased by 10dB - the difference in auditory perception is doubled, that is, the perceived noise is reduced by half;
The sound insulation is increased by 5dB - the hearing can clearly perceive the difference, no matter whether the hearing is sensitive or not;
The sound insulation is increased by 3dB - the hearing can only perceive a slight difference, but the person behind the ear may not perceive it;
1dB increase in sound insulation - almost indistinguishable by the human ear.
This suggests that if we want to improve the sound insulation effect of the glass, the weighted sound insulation Rw should be increased by at least about 3dB, and if we want to significantly improve the sound insulation effect of the glass, the Rw should be increased by at least 5dB.
Glass Sound Insulation Formula
The sound insulation of glass is a logarithmic function of the quality of the glass and the frequency of the sound, and obeys the following laws:
R=20lgM+ 20lgf-47.2(dB)
In the formula:
R - the sound insulation of the glass, dB;
M - mass per unit area of glass, kg/m²;
f - the frequency of the incident sound, Hz.
The only thing related to the glass is the quality of the glass, which means that when the size of the glass is determined, the thicker the glass, the better the sound insulation effect.
Improve Glass Sound Insulation
For different glass, the following measures can be taken to improve the sound insulation:
- Single piece of glass: The thickness of the glass can be increased to improve the sound insulation.
- Insulating glass: In addition to increasing the thickness of the glass, the thickness of the gas layer can also be increased, and the inert gas Ar can be filled to improve the sound insulation because the sound wave propagates in the gas as a mechanical wave of longitudinal vibration, and the longer the propagation distance, the higher the molecular weight of the gas. The greater the loss.
- Laminated glass: increase the thickness of the glass to improve the sound insulation, and the test proves that the increase in the thickness of PVB does not contribute much.
Sound Insulation Improving Limitations
In order to obtain the best sound insulation performance, the contribution of glass thickness, air layer, interlayer film, etc. must be comprehensively utilized. The practical experience shows that the best glass configuration is: unequal thickness laminated glass + 16Ar + unequal thickness laminated glass; Considering the economy, you can also choose: unequal thickness laminated glass + 16Ar + unequal thickness single glass. The thickness of each piece of glass constituting the composite structural glass is preferably different so that the resonance peak of the glass can be avoided. Even so, it is very difficult for glass to increase the Rw greater than 40dB, and the glass will be very thick when it is increased to 45dB.
