Home Theater Treatment For Great Images
Front view of My A/V Room with the screen down
Introduction
So after spending your hard earned cash on that new projector and screen, there is more to installing them than just hanging them off the ceiling or putting the projector on a table or shelf! Especially if you want to get the best possible image.
So by now you will have realized that a projection screen, no matter what it is made of, simply reflects back the light that hits it. In this case all you want it to reflect back, is the light from the projector and no light, or very little light, from anything else in the room.
For those of you who new to screens, their performance and selection it might first be worth reading my post on selecting a screen. It will get you ‘into the groove’.
Projectors require a different approach to their use compared to a flat panel display if you want to achieve an image that is even close to what the projector can actually create. Flat panel displays project light from a surface that cannot easily be interfered with by the rooms ambient lighting. Yes the BLACK screen surface and glass can reflect a little of the rooms ambient light, but compared to the WHITE highly reflective surface of a projection screen their reflection coefficient is very low. This results in flat panel displays that can provide exceptionally high contrast ratios and well saturated correct colors even in rooms with moderate lighting.
In this new world of High Dynamimc Range (HDR) and Wide Color Gamut (WCG), achieving high brightness and saturated color levels with corresponding deep blacks is what gives the image a real 3D feel with impact and depth (not really pixel count). Even modern HT projectors cannot create brightness levels that come close to a modern flat panel display. For a typical large screen projector, luminance levels may not exceed 200 nits (3.426 nits =1 lumen) where as for a modern LCD display levels of well in excess of 1000 nits is easily achievable. Also, with modern rear flat panel lighting techniques, levels of several thousand nits can be achieved over small areas of the screen, (The Sony X1 Ultimate Full-Spec HDR 8K Display can achieve a brightness of 10,000nits). With most modern flat panels generally having very good black levels, very high contrast ratios may be achieved even in a moderately well lit room. OLED’s can achieve 1,000,000:1 under the correct lighting conditions.
Projectors canot create these levels of brightness over their associated large screens. Remember that there is only a single bulb or three small low power lasers that have to illuminate a screen that may have a diagonal as large as 150″ or more. So in order to achieve high dynamic range from a projector, if you can’t get the brightness, you have to have exceptionally deep blacks. While this can give you contrast ratios, in excess of 150,000:1, there is NO substitute for brightness for a true HDR image.
Having exceptionally high brightness levels for a projector, even if it could be accomplished, is not necessarily what you might want to have. The 10,000nit level specified to meet the Dolby Vision HDR spec is ONLY to support what are known as specular highlights. These are very small areas of the screen like stars, candles flames etc. just like those levels found in real life. Producing levels like that across the entire screen is not only currently impossible but would potentially create significant eye strain with very large screens.
So where does this leave us in creating a satisfactory viewing environment for projected HDR images?
Treatment
The goal is to reduce, to a minimum, any light striking the screen that is not directly from the projectors lens. Light striking the screen from none projector sources will only serve to reduce dynamic range (wash out the image) and change the images color based upon the color of light reflected back to the screen.
It goes without saying that the theoretical ideal room for projection is one that is as dark as a bat cave and has no reflected light from any surface. This would mean no light sources of any kind in the room AND surfaces that were totally absorptive to the light reflected from the screen. For almost all of us, this just not practical, and of course many of our partners would never accept such a room environment. I have seen images of HT rooms, that like mine, are totally sealed from external light but all the walls are covered in draped black velvet (an excellent light absorber) and the floors and ceilings use matt black paint and black carpet. Excellent treatments to extract the very maximum contrast ratios from your projector. Making the average Egyptian tomb look really inviting! It also has a profound effect on the rooms acoustics.
So for the rest of us, there are several areas we can explore to improve our images dynamic range and color accuracy:
- Put dark curtains or blinds on every window to stop light from entering the room and close all doors if possible.
- Select a screen that has a suitable gain and appropriate viewing angle performance. This will help reject off axis light reflections.
- Position the projector correctly with regard to the type of screen:
- Angular reflective screen material
- Retro-reflective screen material
- Install non-reflective dark materials immediately adjacent to the screen. Above, below and on the walls.
- Don’t have a large reflective surface opposite the screen such as the opposing wall. (see my diffuser solution below)
- Ideally turn off all lights and equipment displays when watching your movie.
- Don’t have white colored walls, furnishings and carpets etc.
- If black is not possible, use darkish colored wall paper and or paints. I recommend earth tones like dark browns and grays, deep reds, and purples, and dark blues. Brighter colors like yellows, cyans and in particular any greens I have found really alter the images color balance.
- Make sure that your screen has an absorptive black border. (a great use for black flocking tape)
- Absorb/block any light that might ‘spill’ from the projectors body or outside of its lens angle.
Reviewing my own room shown below, you can see that I have adhered to all of the above requirements. Well almost all of them. The only light sources left on in the room during viewing are the power LED’s for the rear and side powered speakers, rear subs and projector. These small LED point sources of light are irrelevant when compared to the remaining light reflections from the red/brown walls and black/gold carpet. However, in a totally black room with the projector off, these tiny light sources still manage to illuminate the screen so that it can be seen. So ideally make sure that any background reflected screen light is lower than the black level created by your projector. In my case this illumination level is much lower than the black level of my projector, so it can be ignored.
Front of my room prior to ceiling absorbers – screen retracted
Front of my room after the installation of ceiling absorbers – screen retracted
Front view with the screen dropped and 16:9 masks descending, showing the black recess for the screen
Had I been a little more anal, I would have covered all of my sound absorbers in black material. However, you still need to feel comfortable in a room, and using all black material might have made the room feel very ‘dreary’. So yes, a little compromise maybe required for those of us us who are not total perfectionists. Remember the old architects adage, ‘Form follows Function’.
Rear Quadratic Diffuser Before Black Out Treatment
Rear Quadratic Diffuser After Black Out Treatment
The two images above clearly show the reduced light reflection that was achieved once my rooms rear quadratic diffuser was treated with a black flocking tape. This had a very noticeable improvement on black levels during moderately lit scenes that also contained darker images. Making those images noticeably more dynamic and giving them improved depth.
Types of Materials
Not all materials, even of the same type and color, are equally absorptive/reflective. Without exception one of the most popular and better light absorbers is hung, pleated black velvet. As I pointed out, be careful, not all black velvets absorb light equally well. This also applies to any black surface/material and depends upon the surfaces finish, shinny or matt and its general depth of texture.
In my case I selected black and red open weave burlap and a dark brown microsuede from AT Acoustics. Depending upon what you are covering, such as speakers and sound absorbers, you must ensure that the sound can pass through the material without attenuating it. This is especially true for speaker covers. Stiff materials if used to cover acoustic traps may reflect certain bands of frequencies, so select materials that are tested as being acoustically passive.
When selecting a material for its light absorbing properties it is always best to either get a sample or to read about other HT enthusiasts experiences on sites like the AVS Forum, and visit various camera and telescope web sites and artists materials suppliers.
Remember that your room is a listening environment too. For many, including myself, the sound may be just as important, or even more important, than the image. So be careful with treating too much surface area with thick fabric. This could cause the room to become too acoustically dead, and create an unpleasnt listening environement.
Recap
The aim of treating a projection room is simple, keep any none projector and any reflected light sources away from the screens surface. So the first rule is select the correct type of screen for your room environment and projector. Remember that in the correct setting, some projectors, like my JVC DILA, can provide exceptionally deep blacks, less than 0.002 lumens. A single candle puts out 12 lumens, a 5W incandescent bulb emits approximately 25 lumens. So it is very easy to see that to reach the projectors black performance residual light sources and reflections in the room must be kept to an absolute minimum.
The good news about all this is that if the room is not too reflective and there are no light sources on then during dark scenes, the screen provides little room illumination so reflected light energy is very low from the rooms surfaces and black levels are maintained. The bigger issue, as I discovered, is during bright scenes that contain dark images. Reflected light from the room under these conditions will cause the darker areas of the screen to be slightly washed out. Here your eyes do help out a little by closing down their iris’s helping to restrict incoming light.
Remember that your eyes are very sensitive to small changes in black levels, and relatively insensitive to changes in high brightness levels. So for projectors in particular, that have a limited light output, it is very important to maintain deep black levels, especially when trying to produce a good representation of an HDR (or SDR) image,
Get black out tape here at J.V. Converting Company.
Get black out materials here at Guildford of Maine, here at Joann’s and here at AT Acoustics.
See my home theater here.
