The Importance of Professional design and planning for home theaters (part III)
We agree that speakers are not like children - they should be heard and not seen. That is not always possible but it is certainly a design goal. But beyond that, and even armed with THX speakers, the placement of the speakers is critical to the attainment of accurate sound reproduction.
They cannot be too close together or too far apart. Depending upon the speaker, one must be concerned with boundary effects, cabinet resonance (when built into a cabinet or theater proscenium), and side wall reflections.
The most difficult speakers to place: the center channel and sub-woofer(s).
The sub-woofer is most affected by room modes. The good news about the bad news 'room modes' is they are very easily calculated. When your designer is involved at the start of the project, the proper placement of the subwoofer can be accurately calculated. The bigger the room the bigger the sub-woofer required.
Once you get into multiple sub-woofers, the design becomes a greater challenge. In one case, the owner of a stereo retail store was concerned the sub-woofer in his demonstration room was not producing adequate bass effect.
To solve the problem, he placed a second sub-woofer in the room, then a third and then a fourth. With each addition, he was not getting the increase in bass volume he expected, and, in fact, the overall quality of the bass was getting worse. The problem came down to two issues.
First, each sub-woofer had been placed one of the four corners of the room - they were all perfectly symmetrical!
In looking at the room modes, the listening position was in the same null zone from each corner. The second reason? Remember, we said you have to be careful about using resilient channel for sound isolation? In this case, the methods used in the store for sound isolation were absorbing the bass frequencies in the room.
The solution? The position of each sub-woofer was changed to re-enforce frequencies at the seating position and smooth out bass response. Now back to the center channel. The minute your designer places the center channel speaker below the screen, find another designer. That's not where it belongs. The absolute best location for the center channel speaker is behind the screen!
When the lips move, that's exactly where the sound comes from. Now your brain does an excellent job in processing sounds to make you "think" sound is coming from a place it is not; but, that is fatiguing and subtracts from your enjoyment of what should be a relaxing environment.
While behind the screen is an ideal location for the center channel, there are indeed cases where that is not physically possible. Where's the second best location? Above the screen.
The problem with achieving correct speaker placement is not placing the speakers during the initial design phase.
The problems occur when the designer becomes involved in the process at too late a stage. If the walls are up, the wire run, the cabinets are in place and the designer comes on the scene, the only recourse is to tear down walls, cabinets and other structure members. If you're spending $30,000 or $100,000 on your theater, you want it to sound like a million bucks, not like $5000.00. The only choice is to tear away.
Lights, Projectors & Screens
As in any special purpose room, attention should be paid to the lighting design. In the case of the home cinema, control of the lights becomes equally important. After all, you want the lights to dim when the movie starts without getting out of your chair. The most commonly used lighting control device used in home theater applications is Lutron's Grafik eye.
This device provides the various lighting 'scenes' needed in a theater and can be easily integrated with theater control systems from Crestron, AMX and others.
Where the theater designer needs to be involved is in the decision process of which lights should remain on, or dimmed, during the movie presentation. One common mistake is the use of tube lights in lighting coves and stairs.
Why? Well, these lights emit a very yellow light. The side effect is often green flesh tones on the screen.
The lighting color is very important. In a properly calibrated theater, you've spent $500 to $1,000 to have a trained Imaging Sciences Foundation (ISF) member carefully color calibrate your projector. (If you were present when this was done, you'll recall the calibration was done with all the lights off in the room.) The front projection screen reflects all light, not just the light from the projector. So, if lights are on in the room, the color of those lights will affect the color fidelity of the picture on the screen.
In most theaters, some lights remain on during the movie presentation. Here again, you must be careful.
Incandescent bulbs change color as they dim. One solution to this problem is to use D65 fluorescent lights. D65 tubes are 6500K in color. Yes, you can dim fluorescent lights when dimming ballasts are installed. Another choice is side emitting fiber optic lights. If you must use incandescent fixtures, your designer can install theatrical filters to correct the color.
The intensity of the lights left on during a presentation also have an effect on picture quality. When you are in your theater, turn off all the lights, close the doors, curtains, drapes, what have you.
What you see is the blackest black you can achieve on the screen. Now raise some of the lights to a low level. This is now the blackest black you can achieve.
There's one other aspect to room lights, more particularly the lighting fixtures themselves, which is often overlooked until too late. Rattles! Many lighting fixtures and sconces have parts that fit together rather loosely. If care is not exercised in the selection of the lighting fixtures, you could be introducing very distracting rattles into the room.
Care should be exercised in the selection of wall finishes and colors. White walls have no place in a home theater!
White will reflect light from the projector and will make it almost impossible to properly calibrate your picture. As the scene in the movie gets lighter, more light is reflected off the white walls on to the screen, washing out the picture. Shiny reflective surfaces are also problematic.
Not only do they have an unfortunate affect on room acoustics, I, for one, want to see only one copy of my movie. I don't want to see it reflected off the surface of the bookcase or in the glass frames over my collection of movie posters.
The point, really, is that care must be taken in the lighting design of the room. The type of care you need, is the type that can only come from an individual trained and experienced in theater applications.
We've already discussed wall treatments for acoustics; but, the colors used in your room can have adverse effects on picture quality. When you turn off all the lights and fire up the projector, you can see the walls, the floor and the ceiling. You can see these items because the light being reflected from the screen is illuminating the room.
The light from the screen (and the projector) is bouncing off room surfaces and being reflected to your eyes. More to the point, this reflected light is also being bounced back to the screen! The reflected light is decreasing the contrast ratio on the screen and washing out the picture.
In this scenario, can you also see that the walls are red (or blue, or yellow)? If you can see those colors, so can your screen!
This reflected light is not only reducing picture contrast, it's also affecting color balance.
None of us are particularly attracted to a solid black or gray room. On the other hand, care must taken in the selection of colors, fabrics and room finishes so you don't diminish the value of all you've spent on electronics, screens and projectors.
There are several manufacturers and sources of screens. These include DaLite, Draper and Stewart. There are also a lot of screens on the market whose heritage is unknown. Screen quality has a direct and marked effect upon the resultant picture quality. When you start cutting the budget, the screen isn't necessarily the place to begin.
Using a $300 OEM, brand X screen for a $40,000 projector, is rather like putting $100 tires on a $60,000 Mercedes Benz. Why spend all that money on the quality, ride, performance and reliability of the Mercedes just to ruin the ride, performance, and perhaps reliability using cheap tires?
Each screen material has its own attributes with respect to gain, reflectance and color shift.
A competent and experienced professional can match the screen to the requirements of the room, its use and the projector.
Screen size is also a vexing problem. We all are tempted to buy the largest screen that will possibly fit on the wall.
What is the ideal screen size? Several studies have been conducted on this issue. The studies have attempted to get the viewer close enough to the screen that part of the action takes place in the viewer's peripheral vision - adding to the sense of involvement in the film. At the same time, as you get closer to the screen you can see more of the defects in the picture. Defects such as line structure and film grain.
For film, the consensus is a subtended angle in the area of 40 degrees. In other words, the angle created between your seating position and each edge of the screen would be 40 degrees. For a 92" wide screen, this would put your seating position at about 10-1/2 feet. For a line tripled and quadrupled picture, this would be about right.
For a standard NTSC television picture, that's way too close. You couldn't see the picture for the line structure.
As screen size increases, the amount of light necessary to properly "light" the screen also increases ... and increases dramatically. This comes from two areas.
First, as the total square inches of screen area increases, the total light output necessary to light the screen increases.
That's pretty intuitive. But that's not the end of the issue. The second comes from the throw distance of the projector. Most projectors must be located a fixed distance from the screen. This distance is a function of screen size. Thus, as the size of the screen increases, the projector must be moved further from the screen in order to project the picture on the entire screen. The physical limitation is that light intensity will decrease with the square of the distance. So, not only does a larger screen have more area needing illumination, we also have to move the projector back, decreasing the amount of light available to fill this added space.
One attribute of projectors, which will be with us for a long time, is the greater the light out of the projector, the greater the cost. It's not a happy day when you've spent $16,000 on an 8" CRT projector and $2,000 on a 135" screen to discover you can't see the picture (and if you could, it would be worse than your $300 27" TV set).
The relationship between screen size and the budget is a close one indeed. It can be real tempting to satisfy a customer's desire for a larger screen letting the result on picture quality be damned.
Projectors come in all sizes and flavors running from just a few thousand dollars to well over $100,000.00. There are "three gun", or CRT projectors, LCD projectors, DLP projectors and even "light canons".
What is appropriate in your application is entirely dependent upon screen size, ambient light conditions, and desired picture quality. There's no rule of thumb here except to say there is a direct relationship between cost and potential picture quality.
Why potential quality? Simply put, it's very easy to make a $50,000 projector produce a $10,000 picture. It takes 4 to 8 hours of work by a skilled and experienced technician to make a $50,000 projector produce a $50,000 picture. You don't want the Chevy mechanic working on your Ferrari do you?
There are several manufacturers of projectors suitable for home cinema use.
The leaders in this area include Runco, Vidikron, and Sony. Be careful about what you hear on the street. While some manufacturers purchase their chassis from suppliers such as Barco, NEC and Electrohome, the resultant product isn't the same. For example, the Runco 933 is based on an NEC projector. But, if you were to buy the NEC (because it cost less), you'd be in for a serious disappointment.
First, the NEC is a class A device and cannot legally be installed in a home. (So what, you say? Discuss the issue with homeowner's insurance agent!)
Secondly, these commercial projectors are not suited, and indeed many cannot handle, the multiple aspect ratios required for film reproduction. In the case of Runco, the electronics are different, the software in the EPROMS is different, and the ergonomics are better suited for film use.
Today, the price of a projector is a very good indicator of its quality and suitability. If the specifications between two projectors look the same, yet one is $3000 less than the other, there really is, somewhere, $3000 difference in the projector. It could be in the electronics, the convergence mechanisms, or even in the quality of the optics.
Don't be fooled by price or swayed by a sales pitch. You want quality and quality is something you must pay for - it's never given away.
Proceed to Home theater design and planning part IV