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Author Topic: video screen for classroom  (Read 3210 times)

Tom Matthews

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video screen for classroom
« on: June 07, 2007, 12:45:48 pm »

Experts,

Our church is presently furnishing a new multi-purpose building.  There is a room in that building that will be a "dedicated classroom."  We envision that it will scheduled as needed for different types of classes.  

Typical AV needs include DVD (and maybe still VHS!) playback.  Our Pastor also wants a screen for his portable video projector and power point slides.  I would like to see some form of sound reinforcement as well as good audio for DVD playback.  

It seems to me that a flat-panel display could serve for both DVD playback and for power-point slides.  Can someone comment on the feasibility of this approach?

Two issues come to my mind.  First, I need to consider the compatibility of various video signals and how they will be switched (in conjunction with audio). This issue includes the signal sources -- should I try for all HDMI?  What is the video format available from the Pastor's laptop computer?  Should I allow for NTSC?  Any advice would be appreciated.

The second issue is that of screen size and selection.

The room is about 29 feet long and 21 feet wide.  The ceiling is flat at 9 feet.  The screen will be on one of the shorter walls, so the maximum distance from the screen will be approximately 24 feet, allowing for a reasonable aisle at the rear.  I suspect that we will rarely, if ever, fill the room to the point that people cannot choose to sit closer to the screen than 24 feet.  

The screen diagonal for a 16:9 can be converted to height, then an often-quoted rule can be applied:  The screen height should be 1/6 to 1/8 of the maximum viewing distance.  

A 60-inch diagonal screen has a height of about 30 inches, so using the 1/8 specification the maximum viewing distance would be  about 20 feet.  This seems to be a reasonable choice for room size.

Based only on what I have read, I would rather have an LCD than a plasma for the qualities of briliance and robustness.  A 60-inch LCD, however, is a considerable expense.  A 46-inch (more easily obtainable as an LCD) would give a maximum diatance of about 15 feet; that is probably going to work for most class sizes but might not be commensurate with the room size.

Has anyone worked on such a design already?  

Tom Matthews
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Brad Weber

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Re: video screen for classroom
« Reply #1 on: June 07, 2007, 03:55:34 pm »

Tom Matthews wrote on Thu, 07 June 2007 12:45

Has anyone worked on such a design already?

Only probably several hundred classrooms, training rooms, conference rooms and similar.  You are running into very common issues and there is no single answer for most of them other than "it depends".

Using a plasma or LCD display for DVD and computer display is definitely viable, it is done all the time.

If you don't mind using the projector/display remote and the sources match the inputs available, then that is the most cost effective approach.  If you have more sources that appropriate inputs or want to centralize the switching then a separate switcher might be a good choice.  If you switch between sources a lot and/or could benefit from a single connection to the projector/display, then a seamless switcher might be an option.

Beware of DVI and HDMI, there can be numerous connectivity issues relating greatly to HDCP copyright protection or cable run lengths.  It's not that these are bad choices, they certainly do offer some advantages, but there are considerations that don't exist with other signal formats.

I am going through the struggle of deciding what signal formats should be supported for a project right now.  For any commercial projects, including churches, I try to always have composite video and VGA (HD15) connections, there are very few possible sources that can't use at least one or the other, so they are probably the most 'universal'.  Beyond that is a matter of what you think might be used on a regular basis.  Component video is often a good choice for DVD, it allows for a quality HD picture without the HDCP issues, but that may the only source you use that for.

LCD versus plasma has gotten to be a more difficult decision.  In general, I will go with LCD where the sources are primarily computer and often use plasmas where the sources are primarily motion video or it is critical video viewing.  While much less susceptible than when they were first introduced, plasmas are subject to burn-in if a static image is left up for a long time.  Some plasma manufacturers incorporate functions to try to minimize the effect of burn-in, they may move the image around a few pixels at a time or may have a way to put up an all white image.

The cost difference is definitely not linear with screen size.  A 57"-60" LCD display might be 3 times the cost of an equivalent 40"-42" display, so sometimes I'll even use two smaller displays instead of one larger one.  With 100'+ LCD displays starting to become available, maybe the prices on the 50"+ ones will drop, but that may be wishful thinking since it is the consumer market driving a lot of this and the manufacturers probably sell hundreds of 40"-42" LCD displays for every 55"-60" one.  The advantage to you on this is that you can probably go to a nearby electronics store and compare the viewing on different screen sizes.

Speaking of consumer displays, you may not care, but many consumer electronics warranties specifically exclude commercial or industrial use, which is basically anything outside a residence.
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Brad Weber
muse Audio Video
www.museav.com

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Re: video screen for classroom
« Reply #1 on: June 07, 2007, 03:55:34 pm »


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