How much space between two windows?-Acoustics Forum-Acoustic Fields Forum

Hi,

We live in a detached / single house. The outer walls are made from brickwork, then some isolation and then an inner wall of concrete. Together, this is about 40 cm / 16 inch thick. The noise from certain noisy cars and motorcycles, from the road about 40 meter (130 feet) further on and also in the street before our house, up to 80 dB(A) outside, and other outside noises bother me. I think the isolating value of the wall is about 50 dB(A), but the windows, even though they are double glass, are dampening the outside noise for 20 dB(A), as far as I can measure this myself with my iPhone 5 app. I’ve tried to find as much information as possible online.

I’m planning on sound-proofing one room first, as a test. If it’s to my satisfaction, I’ll do the rest of the house.

I’m thinking about putting a second window (with 51 dB(A) sound-proof double glass) in front of the existing window and a temporarily improvised isolation of the door with a thick layer of MDF.

I didn’t fill out the room-info because this is not about the inside of my room.

My questions are:
1) 51 dB(A) glass is quite expensive. Of course I could use less thick glass, but I want to do it as silent as possible. How do I know what will be enough?
2) How much space should I keep between the two windows, to prevent a three-leaf effect?

Any good advice would be much appreciated. Thank you.