Fitz is the pro at acoustical solutions no doubt.
Hello guys. Let me CLARIFY some things here. Ralph, your statement, although appreciated mucho, is way too generous, unless, given as sarcassim. Here is my disclaimer. I'm in no way an expert at anything except pissing people off

I even hate to sound like one. But this is a forum for home recording enthusiasts, of which I am one also. I have gained an insight into many things here, thanks to other members who have shared their knowledge and time with us. I just try and pass on what I have learned. It by no means gives me credentials as an expert. I also know from past experience, soundproofing is a difficult at best, impossible under certain circumstances and can waste a lot of hard earned money and time. The best advice I can ever offer here, is truth, at least as I know it. When I am wrong, I know I'll hear about it immedietly. Also, understanding the nature of sound transmission is not something that comes from intuition, instinct, nor second guessing. On the contrary, ST, if anything, defies common sense sometimes.

Sooooo...let me put it this way. The BEST advice I can offer a person is only as good as the information they supply here in regards to what they are really trying to accomplish.
In dobro's case, he was ONLY asking if the carpet tile he applied to a plywood panel inserted into a window opening, would improve the panels ability to impede sound. My answer is not really. It will help dampen vibration in the panel, and absorb certain frequencys ON THE OUTSIDE, not the inside. The panel, when excited by frequencies relative to its size, transfers by way of vibration, the same wavelengths that exite it, to the INSIDE. Make sense? That it has very little mass is the reason. Even 2 layers of sheetrock would perform better.
Also, BECAUSE the panel is only one leaf, it really does little. Even a hollow core door is a two leaf system in a sense. That is why I suggested a frame, with panels on each face and insulation in the void. Even standard wall construction is a two leaf system. However, ANY portion of a room enclosures ability to attenuate sound is only as good as its WEAKEST LINK. You could put a completely sealed slab of concrete in the window. But if the rest of the structural framing, walls, doors, ceiling, floors, HVAC ducting allow transmission to occur at ANY level lower than the concrete, it does NO GOOD!! You still have some leakage into the room via these other paths. Soooo, what do you do? Yea, putting anything in the opening helps to some degree. But SOUNDPROOF it does not. Get my drift? Soundproofing is a misnomer. Total soundproofing is something you have to plan from the ground up. AND it is only as good as the technique detail, materials and distance from sound generation objects.
Even airports, which use some of the best Sound Transmission Class construction and materials, fail to some degree, as aircraft approach the boarding terminals. Well, I hope that gives you a little insight into MY intent here. We all face the same delimas, some more so than others.
I am just trying to clarify the nature of sound transmission. Thats all. Solutions are only as good as the weakest link. Therefore, to soundproof an apartment in Singapore, the best suggestion I could possibly give, is MOVE, as all other attempts are likely to fail given the nature of the apartment as described.

The alternative is LIVE with it. But that brings up another point. How LOUD is the noise? Thats is what were really dealing with here. If you are only trying to impede noise that is 45 db, why build solutions that succeed at 65 db. For EVERY db of increase in noise, it takes TEN TIMES the ability to attenuate it. That is fact, as each increase of db is ten times the previous. So, there you have it. Hope this helps.
fitZ
ps. Ralph, I've already apologized for my disrespect on your thread regarding vocal booths. I am trying to make up for it by keeping to the point here.