My Soundproof windows done by Singapore Windows & Grilles Specialists were FANTASTIC! Compared a few suppliers and found that this factory-direct contractor's price is the most reasonable. Now I can have my peaceful sleep without the noise from the MRT tracks just right out of my windows.
Very sincere contractor. They even helped to check and lubricated all my windows' hinges without additional charges, due to safety issues. Would recommend him if anyone looking for windows and grilles contractors. Below is his contact:-

Louis from Singapore Windows & Grilles Specialists (HP: 9672 0326 / 9100 6846)