Q: What is an acoustically transparent projector screen?
An acoustically transparent projector screen is best suited in a scenario when speakers need to be placed behind the projection screen and you do not want to sound waves to interact with the screen, moving the projection surface and causing distortions to the image or diminishing the quality of the audio by blocking the sound waves.
Acoustically transparent screens work by utilizing negative space in the surface, which allows for the sound waves to travel through without interference from the surface.
These screens are particularly useful when there is not enough space in the screening room to have the speakers placed on the side of the screen and one does not want to get a smaller screen in order to leave room for the speakers on the side.
Many people also prefer the illusion of the character’s voices coming from “behind” the picture as opposed to the sides or beneath it as it emulates the characters talking.
Types of audio transparent screens; Perforated vs. Woven
There are two main types of acoustically transparent screens; perforated screens and woven screens.
Perforated screens are made up of a series of holes with about a 0.3mm diameter or less. Some manufacturers make “micro” perforated materials with a much smaller diameter hole.
These perforations allow the sound to penetrate the screen without allowing much light through, eliminating the possibility of the picture also reflecting from the wall behind through the perforations back to the viewer’s eyes.
Generally, the negative space of the perforations is more noticeable than the negative space in the weave when at a closer viewing distance.
That being said, both the perforations & weave become virtually unnoticeable when seating further than 12’ away from the screen.
This gap continues to shrink as manufacturer’s are using smaller perforations and tighter weaves which is specifically important as the pixel size is shrinking with the adoption of higher resolution projectors.
As opposed to having a single sheet of surface with holes punched into it, a woven screen is made on a loom similar to the way other textiles are woven.
Woven screens have more natural variations in their thickness and pattern, making them more effective in reducing alignment with the projector pixels and reducing the effect of moiré than that of a perforated screen.
These may also lose small amounts of sound at certain frequencies as it is absorbed into the screen, but this can normally be fixed with tone controls and basic equalization.
Woven fabrics, on the other hand, are not quite as good at delivering sound through the screen but they do reduce the potential for a moiré effect and have a less noticeable pattern at a closer viewing distance.
Acoustically Transparent Projector screens and the moiré effect
What is moiré?
The moiré effect refers to the lines and patterns you may see on your projector screen when you are trying to projected video.
The problem is related to resolution; if a pixel cannot be seen a very short distance from the screen, then it is the projector screen that is causing the problem. However, if a pixel can be seen in detail it is the projector which is causing the problem. This is often the case with screens made from fine fabrics.
What is moiré and how does it occur?
Moiré occurs when the natural patterns on your projector screen align/overlap with the pixel patterns of what is being projected, merging to form lines that run across your screen. This can occur when the projection screen has too loose of a weave, perforations that are too large, or an uneven patterning.
Particularly bad cases of moiré will give you feeling that you are viewing your screen through a mesh screen door.
Moiré is becoming a larger issue now with 1080p+ HD projectors; The higher resolution makes the projected image more susceptible to imperfections on a textured screen compared to a smooth “HD” surface.
Most acoustically transparent screens have no issue with moire effect on a 720p resolution projector, however the greater the projection resolution, the smaller the pixel and the higher the probability of moiré.
“Generally” speaking, with screens 10ft wide and above, moire from the perforations or weave will not be a problem.
Place a plain white piece of paper against the screen exhibiting moire. If the pattern is still present on thepaper, then it is a result of the projector.
If the moire is not visible on the piece of paper than it is due to the screen. This is often the case when a 1080p+ projector is being used on an acoustically transparent surface with a loser weave, larger perforations or a non smooth surface.
The moiré effect can be prevented by the use of a smoother projection screen intended for use with 1080p+ projectors.
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