Audio Excellence

Congratulations! You are about to install a Home Theater system in your client’s home and are aiming for top-notch results. Your client satisfaction will be your pride and as a part of your reward, it will help to build your reputation. 
You must achieve the best, and the fundamental aim is to provide this most desired ‘suspension of disbelief’, also called total immersion.

I will now introduce the basic 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 condition # 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 programs that are played on the system are not music, but movie soundtracks.

So, I will rather use “realism” as the most desired criterion.

The good news is that realistic sound reproduction is also “musical”, provided the music has been correctly recorded.

For the sound to be “realistic”, there are many criteria to be met, but the very first one I would draw your attention to 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.

The fundamental implication of this is 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 Theater, all the sound supposed to come from the visible action (on the screen) has to go through the screen: The speakers cannot be placed in front of the screen, as nobody would like an image that is projected directly onto loudspeakers…

So the speakers must be behind the screen.

This of course means that the screen has to be acoustically transparent, or A.T. as we will refer to it.

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

1. How to get 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 a significantly better image.

Today, there are projectors with 4K resolution available in the residential market, either by native resolution or by interpolation (E-shift).

Even if the source is not native 4K, these projectors offer a significantly better image than HD ones. 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 projection surface, which is compatible with resolutions beyond 4K.

This projection surface will make things very simple for you, as it does not degrade imaging quality at all (This is not the case with most other A.T. projection surfaces).

The screen platform really depends on what you need. It can be fixed-frame, retractable, flat or curved, with or without masks, according to what is specified. 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 would recommend 2.37/1 if you are using an anamorphic lens, 2.35/1 otherwise or 2.40/1.

16/9 is not a movie standard, but a TV standard. And to provide a really stunning 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 these would typically provide too narrow a soundstage.

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

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 theaters. 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 Theater is about double that of the SMPTE one. This is because commercial theater rooms are quite dark and more or less normalized in terms of ambient light.

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

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 lumens output from the projector.

This is in theory.

In practice, you have to be aware that the available brightness of projectors is always overrated: After proper calibration, some projectors are only providing 1/5 of the claimed brightness output. Some tests performed by independent journalists provide the actual measurements of the projector’s brightness after calibration, which is much more trustworthy data.

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 installation a stunning one: The sound.

As it is far more complicated than video, I will have to chop the subject into quite a few sub-chapters.

All the best,

Patrice Congard