What kind of projector? What kind of Screen? All of these things are vitally important.
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Hello, in the directions to my sharp projector it tells me approx. how large the image will be with different length throws and it lists up to 58.4ft. minimum throw and on that catagory it doesn't list a maximum which means to me that you can put the thing 70 feet away and just zoom way in and still get a great picture, I had(I use past tense because my projector fried in a recent electrical storm, and I am now dealing with the insurance company) a 15ft throw and it made the image 100" and a GREAT picture with progressive scan and a good component video cable and a complementing screen it is very enjoyable as long as your room isn't too bright- so there are a lot of factors with front projectors to ensure truly good results. FWIW the 58.4 ft minmum indicates a 500in image that it will produce :) I don't think 20ft is too far by any means just means you'll have potential for a HUGE image.
Attainable???...Yes. Practical???...Here are the issues.
You didn't specify which projector you would use. Knowing the projector would indicate the lens ratio. A simple equation is to divide the throw distance by the lens ratio and you will get your screen width. Assuming a 20' throw (LENS to screen) and a lens ratio of 1.5 (just a general assumption), your screen width would be 13.3'. This gives you a screen height of 10', assuming a 3 x 4 aspect ratio. Since we don't know how bright the projector is and how much ambient light is in the room at any given time, there are more factors to explore. I realize I made quite a few assumptions, but if you fill in the missing info I can make some suggestions.
Rayd, I'm hoping to get suggestions here for a used projector under $5000. There is only one window in the place, it is 12 ft by 12 ft at one end of the room. I have a window covering that will make the room pitch black. Other than the window, there is no other external light source. I've just began my HT quest and I have no experience with projectors at all. All I know is that I have the room for a big picture and I don't want a big screen tv console mucking up my 2 channel setup. I have to do some research to understand things like lens ratio, ambient light and other projector nomenclature.
Mitch, like any audio component you can audition at home, have you considered auditioning a projector in your room? You didn't mention if you were interested in LCD, DLP, CRT, ILA, etc., or if you were buying used from a dealer or from Audiogon, but if you can audition a projector in your room you will gain answers to many of your questions. Many LCD and DLP projectors are small enough to make an audition quite simple to do. I applaud you for wanting to do your homework.
I asked about what the equip. was because the type makes a huge difference. If you wanted CRT as opposed to lcd or dila all of this would factor into both screen size and distance. Each of these projectors depending on tube size or spec. has a fairly precise mathematical formula for determining distance to screen size. Also picture quality should be of parmount importance and CRT by a small edge still has the best overall picture quality, but light becomes a greater consideration. Another question is budget. It seems that your application would call for a DILA or LCd because you can generally use these at greater distance from the screen with larger screen size and still maintain decent quality. Dila is the latest and greatest and expensive. 9" CRTs might meet your needs with a 16:( 110" or greater screen. The prob. there is that a lot people have big bad screen envy and sacrifice quality for size. Big screen translate generally into quality degradation. Bottom line whats your budget? How picky are you? ECT.
Gosh, one thing you're gonna have to investigate is how much light you're really going to have falling on the screen. 20 foot throw distances are at the further limit of capability for units designed for home use. Unfortunately light is an inverse square thing, so the further you are sending the light, the more it disperses - and quickly.
The other, consequent problem can be addressed, albeit usually at some expense. Namely, the longer the throw distance, the more area the image occupies - and therefore, the more that has to be lit up. You can get a special long-throw lens for some (most?) projectors, but they aren't cheap and are only rarely included in used projectors.
Because of these considerations, I'd steer you away from CRT units, since they have the least light to begin with. The LCD units conversely appear to have the greatest net light output; they tend to be a bit newer also, and therefore long-throw lenses are somewhat less nearly impossible to locate for a used unit. (GOt that torturous english? :)
Actually, in a loft, you might actually prefer to use a unit that was really designed for the commercial business presentation marketplace. These tend to be a little noisier, have longer throw lenses, and sometimes don't handle motion nearly as well. But some of them are pretty darn good, and they may fit your particulars better than many of the more conventional choices.
I'd also carefully consider your screen options. They can help make up for light deficits in some cases, as they can be obtained with "gain" of up to 1.3x or even 1.5x. The gain is produced by narrowing viewing angle, so it's not a free lunch - but again, your situation may call for it.
I can imagine the kind of issues you may have finding speakers that fill your space! You have 7x as much volume as I do!!!
Actually, the speakers that I have are more than emough to fill the space.....they are Infinity Kappa 9....front and rear. They sound incredible.
I went ahead and bought a 61 inch 4:3 analog big screen. It worked out pretty well. I'm still hankering for a projector that can throw an image across a 120 inch screen.