Sound is heard through the weakest link, adversely the loudest sounds are heard; Example: If you are in a group of people who are talking, you must speak louder in order to be heard. The ability for something to reduce the amount of sound that passes through it is measured in STC or Sound Transmission Class - it is expressed on a scale of 0-100. 100 means complete soundproofing. To achieve an STC 100 would mean zero windows and concrete walls about 3 feet thick. A typical house with brick walls would have an STC of approximately 60-65 on the walls. The problem is the windows - a typical thermal window with 5/8" airspace has an STC rating of approximately 27-29. Therefore, the majority of the noise you hear is coming through your windows.
A bquiet Window is a second window that is placed on the inside of your existing window. It consists of 6mm laminated glass with a minimum 030 laminate and heavy gauge aluminum frames that adapt to any interior. Think of it as a sophisticated storm window. In rare situations it can be mounted on the outside also. The goal is to mount the soundproof window at least 3-4 inches away from the glass of the existing window. Sound reduction is achieved with density and space. The further away the soundproof window is placed, the greater the sound reduction. For example, a soundproof window that is located 4 1/2" away from the existing window has a 3-5 point higher STC rating compared to one that is located 2 1/2" away.
See the Soundproofing 101 page for statistics that prove how effective bquiet windows are.
Sound reduction is measured in STC, which stands for Sound Transmission Class. It ranges from 0-100. 100 representing complete soundproofing and 0 representing no barrier between you and the sound. Example: If have a window open, all the sound you hear is at 0 STC. When you close the window you are now hearing the sound through a barrier (glass). The glass has an STC rating that refers to the amount of sound it has reduced.