Light steel keel gypsum board partition wall insulation effect!
You said the light steel keel gypsum board partition is a lightweight sheet wall. There is a general rule for partition sound insulation, that is, the heavier the material (surface density, or the greater the mass per unit area), the better the sound insulation effect.
According to your program to reduce 30 dB certainly no problem, but the actual noise level there are low-frequency noise, low-frequency noise penetration is strong, after the completion of the final or less than the ideal sound insulation.
It is recommended that you use the following structure: from the original wall 3-5cm do light steel keel (50mm) + gypsum board + light steel keel (50mm) + sound insulation + gypsum board + sound insulation + gypsum board (keel internal sound insulation cotton)
So finished after the volume can be up to 55 dB or more.
Gypsum board are almost, gypsum board must be added between the rock wool, so the sound insulation will be better. Gypsum board is best thicker, 12mm thick or 15mm thick