AVS Forum banner
Status
Not open for further replies.
1 - 20 of 22 Posts

·
Registered
Joined
·
190 Posts
Discussion Starter · #1 ·
I am currently wiring up my home for a projector and screen. I am looking into getting a DLP projector and a 110inch screen.


My question is, what is the optimal distance between the screen and projector? And how far should the electrical outlet be from the projector? Does anyone have any other suggestions?


Thanks,

Nav
 

·
Registered
Joined
·
479 Posts
I don't think there is any "optimal" distance between a projector and a screen. Each projector has a unique throw distance. For a certain projector to fill a 110" screen, it will have to be within a predefined distance range. However, I think most would recommend that you place the projector as far from the seating position as possible within this range to minimize apparent projector fan noise.


See this thread regarding outlet distance:

http://www.avsforum.com/avs-vb/showt...threadid=85653
 

·
Registered
Joined
·
4,720 Posts
Nav,


There really isn't an "optimal" distance.


As long as you are within the throw range of the projector - i.e. as long as the lens can

focus the image at that distance - it will work.


If you have a short throw - you will have more pixels per unit area - but the image will be

small and subtend a smaller portion of your view.


At a long throw - you will have a bigger image, but the number of pixels per area is smaller.


The way to look at it is - regardless of the throw the projector is producing an image with a given

number of pixels - and that's what you see.


Greg
 

·
Registered
Joined
·
609 Posts
I want to point out there is however a optimal distance from the screen to the viewer !.


3 picture hights away is the closest you want to be. PERIOD.


4 is better.


This distace will then allow you to decide on screen size and then throw distance.


I believe for each projector there IS a optimal distance which is governed by the lens parameters. Sort of a optical sweet spot. This varies from lens to lens.


Before you get to any of that you must first decide on where you chair will be in relation to the screen. To keep the 3-4 PH rule that may dictate a different size screen and change the throw distance.
 

·
Registered
Joined
·
2,091 Posts
"3 picture hights away is the closest you want to be. PERIOD.


4 is better"


Seating distance from the screen is a personal choice and I don't think absolutes can be made where to sit. I like to sit closer, filling up a greater field of view. IMO if you sit far away then what's the point of having a FP, might as well have a diret view 27".
 

·
Registered
Joined
·
2,969 Posts
I think what Chris is suggesting with the 3-4 PH distance makes sense if a digital projector is contemplated. Any closer and one runs the risk of noticing digital structure (Screen Door).
 

·
Registered
Joined
·
2,091 Posts
There are so many other aspects to consider such as resolution of the projector, display type (DILA, DLP, LCD), use of an anamorphic lens, and type of screen that I don't think a blanket statement can be made about digital projector seating distance. A digital projector can be configured to display a wonderful image from a closer seating distance without artifacts.


An SVGA LCD would look better at 4 x versus a DILA which has greater fill factor and virtually no screen door.
 

·
Registered
Joined
·
6,225 Posts
Actually, there is a widely accepted means of determining both the minimum and maximum seating distances. The SMPTE (Society of Motion Picture Theater Engineers) has established standards based on long experience and many many polls of theater viewers preferences. I will summarize these and then refer you to more detailed documentation.


A concept called "subtended angle" is used to ensure that the emotional involvement with the material is present. The standard is that the screen height should subtend 15 degrees or more of the viewer's vision, and the screen width 30 degrees or more. If you fail to meet both or either of these criteria, the experience is small screen (watching TV, a part time activity) versus bigscreen (total immersion). In practice, once you decide upon the aspect ratio of the screen, simple trignometry is used to calculate the maximum seating distance to ensure that the rear seats get the bigscreen experience.


The minimum viewing distance is a little more subjective and does indeed depend upon projector type and resolution. Quite simply, the front row of seating should be back beyond the point where the picture structure becomes visible. In a commercial theater, film grain is the picture structure, and you can sit very close to a huge screen because the film is effectively very high resolution. In a home theater, the minimum distance for a CRT is back beyond where you can see scan lines, and for a digital projector is back beyond where you can distinguish pixels. The subjective part is because not everyone has perfect vision. A further factor of course is the type and resolution of the projector.


Most CRT projectors are effectively analog multi-scan displays capable of more than one video mode. If you drive such a projector with an NTSC video source, you get quite a coarse low resolution picture you would not want to sit very close to - but if you use a line doubler/scaler or HTPC scaling to effectively reduce scanline visibility, you can sit much closer without the picture structure intruding upon the viewing experience.


Digital projectors should always be driven at native panel resolution wherever possible, after scaling the source material to this size. The type of projector and the panel resolution both play into how close you can sit before noticing pixels. The commonly accepted rankings by type rank the DiLA (and other LCOS technologies) first and the LCD last, with the DLPs in the middle.


In my family room I use a 4:3 screen in a 90" diagonal size, and an XGA resolution LCD projector. In this room, I can exceed both the horizontal and vertical subtended angle minimums, and also not notice pixel structure, sitting between 9 and 12 feet back from the screen - therefore I have one row of seating. YMMV - I have noticed that when I have guests, the adults prefer to sit back where I have the furniture, whereas the kids prefer beanbags and pillows closer to the screen. I have learned to simply not comment upon these choices, not to worry about the audio "sweet spot" and pixel visibility - because in truth, these are not problems to anyone else unless you point them out!


The reference for the above material is:

http://www.dolby.com/movies/m.in.0009.screensize.html


Gary
 

·
Registered
Joined
·
4,075 Posts
Wow, that's a very neat calculator. I figured out my arrangement based on seating distance = 2 x screen width, plus the throw requirements of the Boxlight 38T/Sanyo XP21N. Your spreadsheet shows it comes right out on the money.


I believe the 2 x screen width rule of thumb is intended for XGA DLP but it also seems to work quite nice with XGA LCD.


Dan
 

·
Registered
Joined
·
6,225 Posts
Nav, I just noticed I only addressed one of your questions, and didn't give an exact answer at that.


The projector to screen distance depends upon the "throw distance" which varies from one model to the next. You have already selected 110" screen (hopefully the same shape as the projector panel to keep the math simple), so go to the web site below, click the "Manufacturer" link in the right column, select and click the manufacturer, select and click your model projector, and click the "Projection Calculator". Enter the 110" diagonal screen size and click "calculate". You will either get a narrow range of projector to screen distance (for a model with focus adjustment only) or a wider range (for a projector with zoom lens). Stay somewhere between the two limits given.

http://www.projectorcentral.com/


The electrical receptacle should be no further from the projector than the power cord length. Best results are often obtained when you power the projector and other audio/video gear from the same circuit, to avoid audible or visible noise called "ground loop". If you have cable TV or telephone line connections to any of the interconnected A/V equipment, these connections are notorious for the above "ground loop" problem, but you can get "ground isolators" to eliminate the problem.


Gary
 

·
Registered
Joined
·
609 Posts
The 3-4 is from the SMPTE specs, and what I refer to. Gary, Great post.


INDEED it IS personal preference. I WHOLLY AGREE.


What im refering to is different than what has been discussed.


Your SOURCE material and device determine safe distance. Sure using good HiDef you can sit 2 PW away. However, Std Def and in particular BAD std def like DSS or Cable require a further distance to obscure the SOURCE structure. An example would be the marco block size in DSS type MPEG compression. These 'blocks" are somewhat like pixels and are tuned to be viewed on a 27" picture with a very small angle of view. As you get closer/bigger then this MPEG blocky nature will become more obvious and less appealing. The SMPTE specs really don't account for this.


Bad Cable also produces this problem for different reasons.


YES the pixilated structure of the imager in the projector is also a problem its more how these interact with the blocky nature of MPEG and DSS to produce a weird sorta alisasing that is best viewed from a distance of 3-4 PH.


DVD of course also has block structure. Once again its not so much the SMPTE specs but the source device that requires a distance.

All that said however


It is personal choice. However I think its best to realize its possible to be to close and look at a picture and decide BEFORE the entire room is commited to in stone.

Quote:
Gary
The electrical receptacle should be no further from the projector than the power cord length. Best results are often obtained when you power the projector and other audio/video gear from the same circuit, to avoid audible or visible noise called "ground loop". If you have cable TV or telephone line connections to any of the interconnected A/V equipment, these connections are notorious for the above "ground loop" problem, but you can get "ground isolators" to eliminate the problem.
This point is VERY important.....
 

·
Registered
Joined
·
479 Posts
How would I know if I had a "ground loop" problem? What are "ground loop" isolators? Do they attach to the cable causing the problem (CATV cable, phone line) or to electrical outlets?
 

·
Registered
Joined
·
6,660 Posts
Then.. there is the other important criterea, when utilizing a digital projector. A quote from the screen forum.

~~~~~~~~~~~~~~

"Here's the story regarding digital projectors and grey screens.


It involves human nature, as a situational in this comedy.


People want quick, easy answers, for situations that really don't have any. They want simplicity in their lives,where there really isn't any. Take a look at the current political situation, if you want to know what I mean. People will believe anything,as long as it is easy to swallow,and lead to where they want the truth to be. Destroy reality, for a sense of comfort.


back to screens,and greys.


there is no simple grey screen formulation.


One:

you can choose a single grey type and tone. then, adjust your screen size, so the lumen count (at so-called black level) compliments the room lighting,and projector output per square foot of screen. So, the size is adjusted up-and-down..to get to the right perceived black level, to match that of what the screen-projector-room combination will produce. Simple.


Two:

Or, select screen size. then, take into account the lumen count of the projector, the ambient condition of lighting in the room, how the room behaves with projected light, the inherent black level of the projector in question,and then... get the appropriate grey level for that screen size-situation. The black level (or zero IRE condition) of the PJ in question is the key here, in combination with the light output thrown on the screen per sq.ft.



These two scenarios are created by the fact that the digital PJ's have a CONSTANT LIGHT OUTPUT. the bulb output NEVER VARIES. When this happens, the ends of the contrast range spectrum are LOCKED IN STONE. Absolutely un-movable. Period.


So, you have to get the EXACT right grey level screen, to maximize the contrast range you get from the PJ. If not, you are throwing Contrast range away..as far as the eye-brain mechanism perceives it, in conjunction with a given grey screen.


Thus.. it is easy to see, with the incredible multitude of projector designs out there..that there is NO perfect grey screen, period.


Each situation must be tuned for, and by, itself.


Which is why I wanted to market paint systems for self created grey screens. Different greys,and different COLOR CORRECTIONS, to allow for different bulb types... that color shift, the ENTIRE spectra. UHP bulbs are prime offenders, for instance. Color correction can be enabled in the PJ, which many are strating to do..but this limits contrast range and color gamut, in a device that has little room to shift within, in the first place. It is better to zero the color correction in the PJ, back to where it would be, if the bulb output spectra where perfect.. gain greater color gamut on the chip-electronics level..and correct at the screen, for whole spectra shift. Correct the bulb, and black level, at the screen.


The first grey screen color corrected for bulb type, was made for UHP bulb, single panel, bad red, DLP projectors, quite a while back. I sent it to Alan, here at the forum, just for fun. He loved it. He said it corrected the color beautifully, and the black level as well. It's too bad I was far from marketing it at the time.


So, multiple grey, color corrected mixes are clearly the way to go, once you understand what is going on with that digital PJ.


Is that a little more clear?"

~~~~~~~~~~~~~~~~~~~~

So, it's not just the size of the screen, its the seating distance/PJ design criteria/room conditions/screen design parameters. THEN you will have an image that is the best it can be.
 

·
Registered
Joined
·
806 Posts
Also keep in mind that most digital projectors have a range of distances since they have zoom lenses and focus controls. That being the case, the farther back the better, for two reasons.


1. The farther back, the quieter they will be at the listener position.


2. All lenses distort at the edges. The less of the lens you use, the less the distortion.


Number 1 can be aleviated with a hush box but less is always better.


Number 2 is typically not an issue, (unless you intend to use either an ISCO or Panamorph), but again less is better.



Phil
 

·
Registered
Joined
·
6,660 Posts
It also makes me wonder if there are any conditional aspects of the combination of zoom/focus that alter contrast ratio at all, due to the fact that such a small lensing system is used..and there are very definite different amounts of the 'lens surface area' used in different PJ positions. i wonder if this plays any part in percieved contrast range and subtulty of image minutae?
 

·
Registered
Joined
·
1,948 Posts
any rules of thumb for screen height vs. eyeball height;

max projector height vs screen height?
 

·
Registered
Joined
·
6,225 Posts
Once again the model of projector determines the difference in projector height and screen height. The projector has a feature called "lens shift" that effectively allows you to offset the projector above or below the screen, to get it out of the field of view of audience members behind it. The manual for the projector has a table of exact dimensions that should be adhered to when planning for such a projector. A very few projectors have adjustable lens shift, but they are rare exceptions.


The bottom line is that before you purchase a projector, you should plan out screen size and aspect ratio, throw distance, projector orientation (ceiling or table mount), and viewer seating locations. After all, the most expensive part of the Home Theater, and the one hardest to change, is not the projector but the room it's in. I made scale drawings of floor plan and elevations and projector location and seating and speaker positions and veiwer seating before I made a final decision on the projector. Then I made a stategic move of selecting a fixed rather than a rollup screen, and using the screen itself for ambient light control of the double-wide window it covers - this saved me $2000 in new light control draperies. The only other window in the room got a room darkening roller shade (about $60) underneath the existing drapes.


It is the detailed planning involved, and the research you have to do before making a plan, that leads me to believe that front projection will remain the exception rather than the rule. Most normal people will probably continue to buy "Theater-In-A-Box" audio and add it to RPTVs and direct-view sets, off-the-shelf solutions.


Gary
 

·
Registered
Joined
·
151 Posts
Gary:


I checked the Projectorcentral.com website....it does NOT have the Sharp 9000 model as one of the choices. Do you know where I can calculate the 'Throw Distance"


I am getting a 123" Grayhawk with a Sharp 9000. My room depth is 20' and I was planning to fix the projector (i.e., throw distance) at 17-18' from the screen. Will this produce the BEST viewing experience???


Thanks

Amar


Quote:
Originally posted by Gary McCoy
Nav, I just noticed I only addressed one of your questions, and didn't give an exact answer at that.


The projector to screen distance depends upon the "throw distance" which varies from one model to the next. You have already selected 110" screen (hopefully the same shape as the projector panel to keep the math simple), so go to the web site below, click the "Manufacturer" link in the right column, select and click the manufacturer, select and click your model projector, and click the "Projection Calculator". Enter the 110" diagonal screen size and click "calculate". You will either get a narrow range of projector to screen distance (for a model with focus adjustment only) or a wider range (for a projector with zoom lens). Stay somewhere between the two limits given.

http://www.projectorcentral.com/


The electrical receptacle should be no further from the projector than the power cord length. Best results are often obtained when you power the projector and other audio/video gear from the same circuit, to avoid audible or visible noise called "ground loop". If you have cable TV or telephone line connections to any of the interconnected A/V equipment, these connections are notorious for the above "ground loop" problem, but you can get "ground isolators" to eliminate the problem.


Gary
 
1 - 20 of 22 Posts
Status
Not open for further replies.
Top