Sunday, 2 March 2014


As an introduction, I have already exposed how I would run a demo. (See  Running Efficient Demo) Now, the demo needs to be a good one, which means that the system needs to be performing as well as it should.

I will now present the conditions to be met to achieve this goal.

1)     The image must be excellent
2)     The sound must be excellent
3)     The image and the sound must be in perfect coherence.

Unusually, I’ll start with criterion # 2, the sound. The reason is that it will have to close a loop with # 1, as you will see.

The first condition for the sound to be good is that it is realistic. This has nothing to do with the audiophile criterion of “musicality”, as the majority of the program that is played on the system is not music, but movie soundtracks.
So, I will rather use the “realism” as the most desired criterion. The good news is that a realistic sound reproduction is also “musical”, provided the music is recorded as it should.

For the sound to be “realistic”, there are many criterion to be met, but the very first one I would draw your attention upon is its location.
Whatever the orientation of the tweeters and all these marketing gimmicks (yes, pivoting tweeters are only marketing gimmicks), we perceive the sound from where its source is actually located, with a precision that increases with frequency.
This means that when the sound is associated with an image, it has to come from the image. Period.

Of course this means that in the case of a Home Theatre, it has to go through the screen, as nobody would like an image that is projected directly onto loudspeakers…

This also means that the screen has to be acoustically transparent, or A.T. as we use to name it.

Now, if the screen is to be A.T., we have to go back to # 1, and this is the loop I was mentioning before: The image must be excellent on an A.T. screen

1 How to get an excellent imaging with an A.T. screen

First select your projector resolution. It has to be full HD minimum. If it can be 4K, you’ll get an even significantly better image.
Today, there are 2 projectors with 4K resolution available in the residential market (professional 4K projectors are very expensive, very bulky, very heavy and very noisy)
One is a true 4K projector
The other one provides an optically interpolated 4K image.
Both are significantly better than HD projectors. The source is not native 4K in most cases yet, but the interpolation processing works remarkably well.

Now, once you have decided the resolution, you need to select the screen. If you are our client (congratulations!), you are projecting on an Enlightor 4K projection surface, which is compatible with resolutions beyond 4K, increasing with the screen size. This projection surface will make things very simple for you, as it does not degrade imaging quality at all (This not being the case of most other A.T. projection surfaces).

Enlightor 4K with metric scale (1 cm)

Once you have chosen a projection surface, you need to decide on what platform (or frame) it will be stretched.
The screen platform really depends on what you want to sell, so it can be fixed-frame, retractable, flat or curved, with or without masks, according to what is needed. It does not have an effect on the actual image quality, as the projection surface is always the same.

What does matter is the size of the screen and the aspect ratio.

For the aspect ratio, I recommend 2.37/1 if you are using an anamorphic lens, 2.35/1 otherwise. 16/9 is not a movie standard, only a TV standard. And to demonstrate a system, you need the spectacular “wow” factor of a wide screen. Also, this aspect ratio is convenient to hide the left and right speakers behind the screen, whereas in 16/9 it would typically provide a too narrow sound stage.

The size is directly depending on the size of the room, the seating distance and how loud the speakers can be (yes, if the speakers cannot handle high SPLs, you’d better shrink all the sizes and get the audience nearer to the screen)..

Now, once you know the size of the screen, you can do the maths.

The unit in use is the Foot-Lambert (Ft-L), 1Ft-L = 1 Lumen / square foot.

The  SMPTE 196 M recommendation specifies 16 Ft-L for commercial theatres. The equation is simple:
Luminosity (Ft-L) = Brightness / Screen area (Sq.ft).

Now, we have to bear in mind that the THX recommendation for Home Theatre is about the double of the SMPTE one. This is because the public theatre rooms are quite dark and more or less normalised in terms of ambient light (also, it can be a bit tempting to increase the light output to make an impressive demo...).

So, how much brightness do we need from the projector?
The first step Is to measure the brightness of the ambient light as reflected by the screen. It is measured in Ft-L too.
Let’s work on an arbitrary example:

If you need a contrast of 1000/1 (a quite good figure, actually), and if your ambient light is 0.02 Ft-L, you will need a 20 Ft-L luminance.

I would like to add a side comment here: Nowadays, projectors manufacturers claim incredible contrast figures, like 100,000/1 or more. This can be true only in 100% dark rooms and with full On/Off measurements. A more realistic figure is given by the checkered board test, in a real room.

Courtesy of Loudness Films Studio. Screen: RF 180 HD

So, if your screen is 120’’ wide with 2.37 aspect ratio, for instance, and the ambient light is 0.02 Ft-L, the screen area will be 10’ x 4.2’ = 42 sq.Ft.
To get a 1000/1 contrast figure, you will need approximately 850 lumen's output from the projector.
This is in theory.
In practise, you have to be aware that the available brightness of the projectors is always overrated: After a proper calibration, some projectors are only providing 1/5 of the claimed brightness output. Some tests performed by independent journalist provide the actual measurements of the projectors brightness after calibration, which is a much more trustworthy data.

From my own experience, I can tell you that the latest JVC -DLA X70 has a sufficient output for a 150” screen, and the Sony VPL-VW 500 can take a 180” without problem, both on Screen Excellence Enlightor 4K (this in a reasonably controlled light environment).

Now, of course, you have to install a proper setup and calibrate the projector. Nothing really difficult there…

In my next article, I will get to the “hardcore” of what will make your demo a stunning one: The sound.
As it is far more complicated than the video, I will have to chop the subject in quite a few sub-chapters.

All the best,

Patrice Congard