Let’s take a look at a real-world example. Screen Research’s ClearPix2 screen fabric has a transparency rating of three percent. That means that 97% of the projected light is stopped by the screen. Three percent of the light passes through the screen. If we place a perfect mirror behind the screen, all of that light will be reflected back, destroying the video experience. If we place a layer of StopLight black backing, with a transparency rating of 10%, between the screen and the mirror, only 0.3% of the original light output is allowed to reflect back off the mirror. A further 90% of this is stopped by its second pass through the StopLight layer. This means that 99.97% of the original projected light is stopped by the simple inclusion of a black backing layer.
An additional effect of having a black backing layer is an improvement in the contrast of the projected image. Blacks are dimmed without affecting the white level or luminosity of any colors.
The goal of an acoustically transparent fabric, such as THX certified ClearPix2, is to combine superb video performance with excellent acoustic perfomance. The same design goal must apply to any black backing layer. In common with ClearPix2, StopLight has a very low acoustic insertion loss resulting is exceptional audio performance.
The combination of ClearPix2 and StopLight gives a maximum linear signal attenutuation of 2dB which requires only a level change in the processor for those loudspeaker channels placed behind the screen. Furthermore, there is no comb filter effect. The frequency response remains smooth and requires no additional equalization.