Many people consult that there is a sound of traffic or low-frequency humming behind the soundproof window, which is generally caused by the resonance of the soundproof window.
Whether the soundproof window can avoid resonant noise is the most critical step to determine success or failure, but many soundproof window manufacturers do not have the step of judging the resonance frequency, nor do they provide sound insulation curves of different frequencies.
This article summarizes the method of judging the resonance of the window, one is to judge whether the model of the soundproof window is suitable before making a soundproof window; Second, after making a soundproof window, when there is a low-frequency humming sound, judge whether the soundproof window has resonated.
1. Before making soundproof windows, judge whether the model of the soundproof window is suitable.
1) Open the window to detect the ambient noise outside your window.
Use a noise meter that can measure the sound pressure level of the octave band, or the spectroid software of the Android mobile phone, and test the frequency of the noise outside the window after opening the window.
Figure 2 shows the test results of the spectroid software, and the noise outside the window is mainly distributed at 50 Hz and 200 Hz;
2) Calculate the frequency of the low-frequency resonance of the business's soundproof windows.
First, use the following formula to calculate the resonance frequency f: of insulating glass (or laminated + insulating glass).
f=60/x
where x is the product of the thickness of a single piece of glass (in mm) and the thickness of the cavity (in m) on one side.
For example, the cavity thickness is 0012m, the glass thickness is 8mm, then x=031, resonance frequency f=60 031 = 194 Hz.
The red curve in Figure 3 shows the measured insulation volume of this type of window, with a resonance frequency (soundproofing defect) of 200 Hz.
Formula Description:1The original formula is related to the sound velocity of glass, and this formula is simplified and only applicable to glass materials;
2.This formula is also applicable to laminated + insulating glass, and the laminated glass can be regarded as a whole;
3) Compare whether the frequencies of the two are close.
The ambient noise of 200 Hz is very close to the resonance frequency of 194 Hz of this window, so it is judged that this hollow soundproof window is not suitable, and low-frequency noise of about 200 Hz will occur after installation.
2. There is a low-frequency hum behind the soundproof window to determine whether resonance occurs.
1) Close the window to measure the main frequency of low-frequency noise.
Refer to Figure 1 to measure the main frequency distribution of humming or traffic sounds when the windows are closed.
2) Calculate the low-frequency resonance frequency of the business's soundproof windows.
Ditto. 3) Compare whether the low-frequency noise frequency and the low-frequency resonance frequency of the soundproof window are the same after the window is closed.
If they are consistent, it can be concluded that the hum or traffic is due to window resonance.
III. Miscellaneous. 1) If the sound of the current after the window is closed, it is suspected that it is caused by anastomosis vibration, and the method of judging is as follows.
Using the formula f=12084 x, calculate the anastomosis frequency of a single piece of glass, where x is the thickness of the glass in mm.
If the frequency of the sound is measured by software, if the two are basically the same, it can be determined that the sound is caused by the glass anastomosis effect.
2) Soundproof window is a relatively complex system engineering, the above is only a method to judge resonance, and the specific selection needs to be comprehensively judged.
Note: The resonance frequency can also be calculated by this formula, f=1150*x y; where x is the sum of the thickness of the glass on both sides; Y is the product of the thickness of the glass on both sides multiplied by the thickness of the cavity and then the root number, and all size units are mm. Example: 8mm thick glass on both sides, cavity thickness 12mm, x=4 (8+8=16 open root number), y=277 (8 * 8 * 12 = 768 open root number), then f = 166 Hz. The frequency of this formula is slightly lower, but this formula can calculate the case of different glass thicknesses on both sides. It can be considered that the resonant frequency is between the frequencies calculated by the two formulas.