Da-lite Hi Power New or Old what did you get? - Page 19 - AVS Forum
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post #541 of 583 Old 01-14-2011, 11:57 AM
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can any long time owners of 2.4 share how it is faring as far as waves go... ?

Thanks,

Rana

a few funny stories from my life ------->http://www.kirtirana.blogspot.com
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post #542 of 583 Old 01-15-2011, 12:35 AM
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Quote:
Originally Posted by Murilo View Post

Complex and varied? My glass beaded was random size placed everywhere, it was not complex and varied.

I understand your a da-lite fan, i was to, the old highpower is still my favorite, but try looking at it from our perspective.

Your missing the point that what we ordered and paid good money for was not what we received.

Also I really dont get how the old fabric is still going to be used in fixed frame yet, if the new stuff is better.

Also the fabric is quite a bit thinner and feels much more flimsy then the sample, not sure how the new stuff can be considered better. Doug confirmed this when he measured the thickness, but i can literally feel a large difference comparing my sample to the screen.

People did complain about the viewing cone, but come on, not at the expense of this much brightness, i dont think when they had the viewing cone in mind, they wanted the gain dropped that much, and thinner rougher fabric.

I also went with the old fabric because it was smooth and easier to clean, this is rougher, and reminds me of my glass beaded really, and if you clean it, it looks like it would wreck like my glass beaded. Which got wrecked when i tried to clean something off of it.

The old highpower sample did not wreck when i tried to clean the sample, it was smooth, sturdy, and cleaned well. A big reason i also chose the highpower and da-lite.

is it ok to clean the newer 2.4 screen ? or does it get wrecked ?

Thanks,

Rana

a few funny stories from my life ------->http://www.kirtirana.blogspot.com
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post #543 of 583 Old 01-15-2011, 04:30 AM - Thread Starter
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It should be fine to clean. I use hydrogen peroxide followed up with denatured alcohol to clean bug marks off my 2.8 with good resulted. If I were you, I would call dalite for a sample so you can test it out. The 2.4 is not as smooth as the 2.8 but I could see (looking at it with a microscope) (see first post) no reason it would not clean. The micro beads are embedded in an emulsify and as long as you do not use something that lease residue behind or rub to hard and physically damage the surface it should be fine.
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post #544 of 583 Old 01-15-2011, 07:50 AM
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bugs ? how do you get bugs on it ?

chasing rattles ......

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post #545 of 583 Old 01-15-2011, 08:10 AM - Thread Starter
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It is a portable and rolls .. pull downs and electrics have this issue.. bugs like bright light.. They can be on the back as well, and when you close the screen.. they are on the front! you would be surprised at how big a nat is when it is squished on your screen!
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post #546 of 583 Old 01-15-2011, 01:33 PM
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All

I have just stumbled into this issue manyu of you seem to have been struggling with for months - and I was hoping some of the more knowledgable of you could help me out.

I plan to buy one of the new JVC X3's that will be ceiling mounted (2.4m from the floor) about 5.5m back from the screen and 20cm off set to one side and the main viewing will be 4.5m from the screen.

I was planning on a 165cm x 295cm screen and was wondering whether the new 2.4 gain HP would be my best bet?

I have used the online gain calc tool and it seems that the gain across the screen is between 1.21 centre, 1.28 right and 1.22 left - which doesnt really make sense to me why the gain at the edges is higher than the centre so I am not sure I made a mistake!

Any help would be really appreciated!


BASIC SETUP (Change the green values as needed to fit your situation.)
What is the type of screen? Specify A for angular reflective or R for retro reflective. (Do not guess at this parameter--it makes a huge difference!) R
What is the manufacturer-published on-axis centerscreen gain of your screen? 2.40
What is the published maximum viewing angle (to one side in degrees off-axis)? 20
What is the centerscreen gain at the published maximum viewing angle? (Don't guess at this either. Consult manufacturer if necessary) 1.00
What is the minimum gain of your screen at large off-axis angles, e.g., 60 degrees? (OK, you may guess here, but make it <= line 13 above.) 0.6
What is the horizontal width of the viewing area of your screen? 295
How high above the room floor is the center of your screen? 117
How high above the room floor is the center of your projector's lens? 230
What is the distance from the front of the lens to the screen? (Measure perpendicular to the screen.) 550
How far back from the screen is the viewing position? (Measure perpendicular to the screen.) 450
How far to the right or left of the screen center is the viewing position? (Use positive distance for right; negative distance for left.) 0
How high above the floor are the viewer's eyes when seated at the viewing position? 90

OPTIONAL SETUP (You may not need to change these values.)
How far is your projector offset to the right or left of your screen center? (Enter positive distance for right; negative distance for left.) 20
Want instead to calculate the gain of screen points above or below mid-screen height? Enter positive distance for above; negative distance for below.) 80
RETRO REFLECTIVE
Coordinate: x y z SCREEN SCREEN SCREEN
Screen Center Point: 0 197 0 LEFT CENTER RIGHT
Screen Right Point: 147.5 197 0 Calculated Error Angle (Degrees): 16.06 16.93 16.86
Screen Left Point: -147.5 197 0

Estimated Screen Gain: 1.28 1.21 1.22
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post #547 of 583 Old 01-15-2011, 02:33 PM
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Quote:
Originally Posted by airscapes View Post

It is a portable and rolls .. pull downs and electrics have this issue.. bugs like bright light.. They can be on the back as well, and when you close the screen.. they are on the front! you would be surprised at how big a nat is when it is squished on your screen!

i guess i am lucky. my 2.8 119" manual has no such issues.
my issue is waves. but when a movie is on, they can't be seen, so its really not an issue.

chasing rattles ......

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post #548 of 583 Old 01-15-2011, 04:42 PM - Thread Starter
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Quote:
Originally Posted by deimh View Post

All

I have just stumbled into this issue manyu of you seem to have been struggling with for months - and I was hoping some of the more knowledgable of you could help me out.



Any help would be really appreciated!



How high above the room floor is the center of your projector's lens? 230

How high above the floor are the viewer's eyes when seated at the viewing position? 90


Those 2 measurements are your problem, they need to be much closer to being the same number if you want to get any value from this screen. So the projector needs to come down or your head needs to come up..
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post #549 of 583 Old 01-16-2011, 05:52 AM
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Quote:
Originally Posted by airscapes View Post

Those 2 measurements are your problem, they need to be much closer to being the same number if you want to get any value from this screen. So the projector needs to come down or your head needs to come up..

Hi Doug

Firstly, many thanks for helping out a complete newbie - very much appreciated!

I'm afraid that its not possible to increase head-height or reduce the height of the projector and hence I'm trying to work out what the best screen is for this comprimise - ie whether to go with the new 2.4 gain HP material (retro-reflective), or just get a tensioned "normal" gain white screen (angular reflective)?

The next questions are whether its better to have the projector closer to the screen (say 4m) which makes the angle from projector-screen-viewing position larger, but the lamp brighter (I assume). Or have the projector further back (say 6.5m) which makes the angle from projector-screen-viewing position smaller (better for retro reflective), but the lamp less bright (I assume)?

The final question is whether I can / should go for such a big screen, say 3m wide - or whether this would make the image too dim / be uncomfortale to view from a position 4.5m back?

I have now read all threads related to this on this and AVForums sites, but I still dont know - perhaps I'm just a bit thick

As you can see I'm quite confused

Please please help!!!

Thanks
Dave
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post #550 of 583 Old 01-16-2011, 06:15 AM - Thread Starter
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Quote:
Originally Posted by deimh View Post

Hi Doug

Firstly, many thanks for helping out a complete newbie - very much appreciated!

I'm afraid that its not possible to increase head-height or reduce the height of the projector and hence I'm trying to work out what the best screen is for this comprimise - ie whether to go with the new 2.4 gain HP material (retro-reflective), or just get a tensioned "normal" gain white screen (angular reflective)?

The next questions are whether its better to have the projector closer to the screen (say 4m) which makes the angle from projector-screen-viewing position larger, but the lamp brighter (I assume). Or have the projector further back (say 6.5m) which makes the angle from projector-screen-viewing position smaller (better for retro reflective), but the lamp less bright (I assume)?

The final question is whether I can / should go for such a big screen, say 3m wide - or whether this would make the image too dim / be uncomfortale to view from a position 4.5m back?

I have now read all threads related to this on this and AVForums sites, but I still dont know - perhaps I'm just a bit thick

As you can see I'm quite confused

Please please help!!!

Thanks
Dave

Taking a look at the projector central calculator, with that projector and a 133" diag screen you would be at 19fl with a 1 gain screen with a fresh lamp which is not a lot of head room once the lamp ages.
http://www.projectorcentral.com/JVC-...ulator-pro.htm
Smaller will be brighter, but size is a personal preference. You would be better off waiting to get the screen after you have the projector. Use it on a white wall or sheet to figure out what size is comfortable for you from your seating distance.

If the projector can not be placed closer to eye level with and extension pole I would think you will be better off with some other screen technology.

Price wise the HP is probably less expensive than a tensioned screen and you will always have the options of lowering the projector at a later time. If your choice is matte white 1.1 tensioned and HP 2.4, I would got with the least expensive option since your image will be about the same on both. The HP is not tensioned and will get waves over time. These will be less noticeable than if it were a matte white screen.

So in a nut shell, you are outside the required parameters for any benefit of the HP, you will run the risk of waves if it is not a fixed frame vrs the tensioned screen. However, you do have the option of making your image brighter in the future by moving your projector. Most folks put the projector in the middle or towards the close to the screen end of the throw but room layout can play into that as well.
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post #551 of 583 Old 01-16-2011, 06:27 AM
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excellent answer airscapes.... !!!

which screen would be 2nd best for deimh after the 2.4 ? how about video spectra ?

Thanks,

Rana

a few funny stories from my life ------->http://www.kirtirana.blogspot.com
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post #552 of 583 Old 01-16-2011, 07:15 AM
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Quote:
Originally Posted by airscapes View Post

Taking a look at the projector central calculator

Doug

This is great - many thanks for the link!

Do you have a feel of how much I would need to lower the projector to get any impact from the HP?

I actually used the screen gain tool on this forum to calculate the gain with the HP and got the following results:

Not sure if I messed up though.

Dave



BASIC SETUP (Change the green values as needed to fit your situation.)
What is the type of screen? Specify A for angular reflective or R for retro reflective. (Do not guess at this parameter--it makes a huge difference!) R
What is the manufacturer-published on-axis centerscreen gain of your screen? 2.40
What is the published maximum viewing angle (to one side in degrees off-axis)? 20
What is the centerscreen gain at the published maximum viewing angle? (Don't guess at this either. Consult manufacturer if necessary) 1.00
What is the minimum gain of your screen at large off-axis angles, e.g., 60 degrees? (OK, you may guess here, but make it <= line 13 above.) 0.6
What is the horizontal width of the viewing area of your screen? 295
How high above the room floor is the center of your screen? 117
How high above the room floor is the center of your projector's lens? 220
What is the distance from the front of the lens to the screen? (Measure perpendicular to the screen.) 400
How far back from the screen is the viewing position? (Measure perpendicular to the screen.) 450
How far to the right or left of the screen center is the viewing position? (Use positive distance for right; negative distance for left.) 0
How high above the floor are the viewer's eyes when seated at the viewing position? 90

OPTIONAL SETUP (You may not need to change these values.)
How far is your projector offset to the right or left of your screen center? (Enter positive distance for right; negative distance for left.) 0
Want instead to calculate the gain of screen points above or below mid-screen height? Enter positive distance for above; negative distance for below.) 80

RETRO REFLECTIVE
Coordinate: x y z SCREEN SCREEN SCREEN
Screen Center Point: 0 197 0 LEFT CENTER RIGHT
Screen Right Point: 147.5 197 0 Calculated Error Angle (Degrees): 15.96 16.67 15.96
Screen Left Point: -147.5 197 0


Estimated Screen Gain: 1.28 1.23 1.28
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post #553 of 583 Old 01-16-2011, 07:22 AM
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i had a queston... the screen gain calculator is by default set for 2.8

if we had to change it for 2.4 what else do we have to change from default values other than 2.8 to 2.4 ?

Thanks

Thanks,

Rana

a few funny stories from my life ------->http://www.kirtirana.blogspot.com
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post #554 of 583 Old 01-16-2011, 07:50 AM
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Quote:
Originally Posted by airscapes View Post

The HP is not tensioned and will get waves over time. These will be less noticeable than if it were a matte white screen.

I wonder if the highlighted claim is justified? Brightness of a point on a matte white screen should not be sensitive to either angle of incidence or viewing angle (within a scale caused by waves). Also, at large error angles the HP acts pretty much like a matte white screen, anyway.

For some time I've been of the opinion that noticeable waves were associated mainly with angular reflective gain screens, which are very sensitive to angle of incidence and viewing angle. Is my opinion misinformed? I'm curious as to what others think about this.
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post #555 of 583 Old 01-16-2011, 07:54 AM
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Quote:
Originally Posted by rana_kirti View Post

i had a queston... the screen gain calculator is by default set for 2.8

if we had to change it for 2.4 what else do we have to change from default values other than 2.8 to 2.4 ?

Thanks

Please see the lower section of post #2 in the Screen Gain Calc thread.
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post #556 of 583 Old 01-17-2011, 05:45 PM
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Quote:
Originally Posted by FLBoy View Post

I wonder if the highlighted claim is justified? Brightness of a point on a matte white screen should not be sensitive to either angle of incidence or viewing angle (within a scale caused by waves).

Maybe those screens aren't as lambertian as they would need to be, or maybe there is something else going on, but in my experience a Da-Lite Matte White screen showed much worse waves than the HP.
Quote:
Originally Posted by FLBoy View Post

Also, at large error angles the HP acts pretty much like a matte white screen, anyway.

But the angle that is relevant to the gain math isn't the big angle from the wave on the screen, it is still the difference between the line from the projector to the point on the screen and the viewer's eyes to the point on the screen. That angle should basically not change any more than a very small amount. The screen itself likely has slightly different gain when turned far enough, but doesn't seem to be much of an issue with normal waves.
Quote:
Originally Posted by FLBoy View Post

For some time I've been of the opinion that noticeable waves were associated mainly with angular reflective gain screens, which are very sensitive to angle of incidence and viewing angle. Is my opinion misinformed? I'm curious as to what others think about this.

I think you are right that those would be the worst. Consider the extreme angular-reflective case of a wavy mirror.

--Darin

This is the AV Science Forum. Please don't be gullible and please do remember the saying, "Fool me once, shame on you. Fool me twice, shame on me."
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post #557 of 583 Old 01-18-2011, 10:14 AM
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I have a 120" diagonal 16x9 2.8 gain high-power screen that I really like. I've been considering going to a CIH 120" wide 2.4:1 screen for a while now (with my room configuration, the current height of a 16x9 image is a little big, but the width of a 2.4:1 letter boxed on the screen is a little small. A 120" wide 2.4:1 would be perfect).

Anyway, I procrastinated and missed the 2.8 high-power availability. Today I entered all of the numbers for my room into FLBoy's excellent screen gain calculator and these are the results it gave me. Boy am I surprised!

Current 2.8 gain HP in my room:
Screen Left: 1.35
Screen Center: 1.39
Screen Right: 1.35

Proposed 2.4 gain (2.4:1) HP in my room:
Screen Left: 1.75
Screen Center: 1.80
Screen Right: 1.75

So, it looks like my procrastination may have paid off!
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post #558 of 583 Old 01-18-2011, 05:33 PM
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Looking at the data provided by Da-Lite, there might not be as much of a difference between the two screens as the screen gain calculator predicted. I'm looking into it.

--Mark
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post #559 of 583 Old 01-18-2011, 06:16 PM
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Deimh,

I noticed the following in your calculations:

Quote:


OPTIONAL SETUP (You may not need to change these values.)
How far is your projector offset to the right or left of your screen center? (Enter positive distance for right; negative distance for left.) 0
Want instead to calculate the gain of screen points above or below mid-screen height? Enter positive distance for above; negative distance for below.) 80

Why did you enter a distance of 80cm for the height offset? It appears that you are trying to measure the gain at the top center of the screen. Most people measure it at the center-center of the screen.

Also, the numbers you entered for the 2.4 gain screen are not correct (at least not according to this post by FLBoy (the spreadsheet's author): http://www.avsforum.com/avs-vb/showt...8#post12697268).

You should be using the following values for the high-power 2.4 gain screen:
ON-AXIS GAIN: 2.4
MAX VIEWING ANGLE (ONE SIDE): 30 DEGREES (AT ONE-HALF THE ON-AXIS GAIN)*
GAIN AT MAX VIEWING ANGLE: 1.2
MIN OFF AXIS GAIN: 0.9

I plugged your screen info into the spreadsheet using the corrected 2.4 gain high-power numbers above, and I get the following for your center of the screen (vertically) gain:
Left: 1.82 Center: 1.79 Right: 1.78

However, I have also found what I think *might* be an issue with the original spreadsheet for high-power material (I sent FLBoy a PM about it).

With a modified spreadsheet, I came up with the following gain for the 2.4 high-power for your room:

Left: 1.55 Center 1.52 Right: 1.51

In either case, this is a very nice gain.
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post #560 of 583 Old 01-18-2011, 06:17 PM
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Quote:
Originally Posted by DrMark View Post

I have a 120" diagonal 16x9 2.8 gain high-power screen that I really like. I've been considering going to a CIH 120" wide 2.4:1 screen for a while now (with my room configuration, the current height of a 16x9 image is a little big, but the width of a 2.4:1 letter boxed on the screen is a little small. A 120" wide 2.4:1 would be perfect).

Anyway, I procrastinated and missed the 2.8 high-power availability. Today I entered all of the numbers for my room into FLBoy's excellent screen gain calculator and these are the results it gave me. Boy am I surprised!

Current 2.8 gain HP in my room:
Screen Left: 1.35
Screen Center: 1.39
Screen Right: 1.35

Proposed 2.4 gain (2.4:1) HP in my room:
Screen Left: 1.75
Screen Center: 1.80
Screen Right: 1.75

So, it looks like my procrastination may have paid off!

See, I just do not know how much weight to put into this calculator. How accurate is it? Where did the calculations come from? Get a sample and test, its really the only sure way
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post #561 of 583 Old 01-18-2011, 07:06 PM
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Quote:
Originally Posted by deimh View Post


The final question is whether I can / should go for such a big screen, say 3m wide - or whether this would make the image too dim / be uncomfortable to view from a position 4.5m back?

Deimh,

There is a very nice room layout spreadsheet available here: http://carltonbale.com/home-theater/...ter-calculator

You enter all of the info about your room and it tells you if you are too close or too far away from the screen for various viewing standards. I plugged in your info, and I found the following:

For this screen size, the THX standard recommends that you sit no further away than 454cm (right where you will be sitting).

The advertised brightness of the JVC X3 is 1300 Lumens. If you believe this number (I don't), then given the screen gain numbers I computed for you, you will have a screen brightness of 37.5 foot-Lamberts (128.5 cd/m^2). This is plenty bright.

The reason that I don't believe the advertised brightness of the projector is that you need to have it calibrated, and you might not want to run it at the maximum iris setting (stopping down the iris will improve the contrast ratio). I found at least one post claiming to have measured the light output of the projector at 800 Lumens (calibrated to D65; high-lamp, wide iris). With this brightness, you would be at 23.1 foot-Lamberts (79.1 cd/m^2). Still plenty bright.

However, you bulb will probably lose half of its brightness as it ages: 400 Lumens (11.5 foot-Lamberts; 39.5 cd/m^2). This is just under the acceptable threshold for a fully darkened room.

Also, if you want to use this projector for 3-D, then you will have less than half of the effective brightness (because of the way shutter glasses work). So, you are more realistically looking at 11.5 foot-Lamberts with a brand new bulb, and 5 foot-Lamberts with a well loved bulb; way too dim).

My recommendation is that if you are buying this projector for 2-D viewing, you will be fine with the high-power 2.4 material. However, if you are buying it for 3-D viewing, you should consider going with a screen that has about half of the area (200cm X 112cm). Since we all want the big-screen look, you can adjust for the smaller screen by sitting closer. If you sit 300cm from the screen, it will appear to be the same size as it would have with the larger screen at a distance of 450cm. You might even be able to put in a second row of seats with this configuration.

--Mark
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post #562 of 583 Old 01-19-2011, 11:10 PM
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Quote:
Originally Posted by newfmp3 View Post

See, I just do not know how much weight to put into this calculator. How accurate is it? Where did the calculations come from? Get a sample and test, its really the only sure way

Quote:
Originally Posted by DrMark View Post

Deimh,

I noticed the following in your calculations:



Why did you enter a distance of 80cm for the height offset? It appears that you are trying to measure the gain at the top center of the screen. Most people measure it at the center-center of the screen.

Also, the numbers you entered for the 2.4 gain screen are not correct (at least not according to this post by FLBoy (the spreadsheet's author): http://www.avsforum.com/avs-vb/showt...8#post12697268).

You should be using the following values for the high-power 2.4 gain screen:
ON-AXIS GAIN: 2.4
MAX VIEWING ANGLE (ONE SIDE): 30 DEGREES (AT ONE-HALF THE ON-AXIS GAIN)*
GAIN AT MAX VIEWING ANGLE: 1.2
MIN OFF AXIS GAIN: 0.9

I plugged your screen info into the spreadsheet using the corrected 2.4 gain high-power numbers above, and I get the following for your center of the screen (vertically) gain:
Left: 1.82 Center: 1.79 Right: 1.78

However, I have also found what I think *might* be an issue with the original spreadsheet for high-power material (I sent FLBoy a PM about it).

With a modified spreadsheet, I came up with the following gain for the 2.4 high-power for your room:

Left: 1.55 Center 1.52 Right: 1.51

In either case, this is a very nice gain.

Has the calculator be updated or is it going to be updated by FLBoy ? Do i need to re-download or change any preset values in it ?

Thanks

Thanks,

Rana

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post #563 of 583 Old 01-20-2011, 04:26 AM - Thread Starter
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Originally Posted by prkrshawn View Post

This is really amazing and more over I do believe that I will be rethinking getting an HP. As per my opinion it will be interesting to know the gain on the new HP. I am looking at a manual as well so if this change has to do with manual screens.

Not sure how much you read, but the old 2.8 is no longer available as of 2011, the new 2.4 is the only HP. There is still nothing else in the same price range that is anything like it. It does not fit everyone's needs but in the proper setup it is a great screen.
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post #564 of 583 Old 01-21-2011, 05:09 PM
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Looks like I got lucky and received one of the last 2.8 (ordered on DEC 29th and received Jan 7th). The picture is definately a huge jump in brightness compared to my old HCCV. I'm also impressed with the build quality of the Cinema Contour from Dalite.

My only regret is not getting the 133" instead of the 119" :P
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post #565 of 583 Old 01-21-2011, 07:52 PM
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Just got mine, 2.4 oh joy. It's a perm wall. I started tearing down my old frame and screen, mounted new frame, and started the snaps,,,,,holy crap. I got the four corners on and a few more then gave up for the night
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post #566 of 583 Old 01-24-2011, 07:00 PM
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Originally Posted by DrMark View Post
Looking at the data provided by Da-Lite, there might not be as much of a difference between the two screens as the screen gain calculator predicted. I'm looking into it.

--Mark
Hello everybody,

I was using the now well known All Screen Gain calculator developed by FLBoy, to compare the difference between a 2.4 gain Da-Lite High-Power screen and a 2.8 gain Da-Lite High-Power screen for my theater. It just happened that my viewing angles line up with measured points on the original gain graph published by Da-Lite (see attached). Unfortunately, the gains listed on the graph didnt match those predicted by the spreadsheet.

After exchanging PMs with FLBoy, I found that the problem came from his attempt to provide a spreadsheet that would work for literally any screen. However, as can be seen from the Da-Lite graph, the high-power material isnt just any screen. So, I decided to develop a customized version of the calculator that will work much more accurately for high-power screens.

I have attached my new spreadsheet to this message. You use it in much the same way as the previous calculator except that because this calculator is customized for high-power screens only, some of the previous inputs are now hard-coded into the spreadsheet.

The next posting will describe how I developed this new spreadsheet so that others can double check my work.

I want to again acknowledge FLBoys work on the original calculator. Without it, I never would have attempted to provide this version.

--Mark

 

High-Power Screen Gain Calc.zip 14.748046875k . file
LL
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post #567 of 583 Old 01-24-2011, 07:08 PM
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Hello everybody,

In this posting, I will describe how I implemented the new high-power screen gain calculator. I want to go into some technical detail here so that others can double-check my work.

I decided to protect and hide the formulas used in the spreadsheet simply to make it simpler for people to use. The spreadsheet does not use a password. To get access to the formulas, simply do the following:
  1. Click on Review and then on Unprotect Sheet
  2. Select rows 30-64 and right-click; select Unhide from the pop-up menu.
The vector calculation math is unchanged from the original all-screen gain calculator.

To better model the change in gain by angle for the high-power screen material, I decided to piece-wise curve fit the measured data. For the following discussion, see the High-Power curve fitting spreadsheet attached to this posting.

To accurately read the data from the Da-Lite graph, I saved a copy of the graph to my PC and opened it in Photoshop. I then turned on the ruler tool and set it up for millimeters. With this tool, I was able to read off the location of each sample point in the Y (gain) dimension. By measuring the location of the origin of the graph, I was able to easily compute how many millimeters in the Y (gain) dimension each data point is. Finally, I derived the gain/mm by measuring the full range of the graph (3.0 gain). Because the data points were measured at even multiples of 5 degrees (e.g., 5, 10, 15 degrees), the X axis values were trivial to determine.

You can see the measurements I took at the top of the spreadsheet.

As a double check of my math, I plotted these points in Excel. This is the first plot in the spreadsheet. You can easily see that the shape of the lines corresponds to the original plot.

I then analyzed each material (2.4 gain and 2.8 gain) separately. By using Excels curve fitting tool, I was able to curve fit polynomials to sections of the measured graph. In the case of the 2.4 gain material, I fit three segments, and in the case of the 2.8 gain material, I only needed to fit two segments. This is shown in the next two graphs.

In order to make sure that the curves are well behaved at the ends of each segment, I fit additional points on both sides, and extended the fit lines so that they can be visually inspected. For example, in the high-power screen gain calculator, I use one curve for the range 0-10 degrees for the 2.4 gain material. In order to make sure that the curve is well behaved at 0 and 10 degrees, I fit the curve from 0-15 degrees, and plotted this fit curve from -5 degrees to 20 degrees. You can see that the R^2 for 0-10 degrees is 1.0 (this is not a surprise, as you can fit any four points perfectly to third degree polynomial.) What is important is that the shape of the red curve looks right beyond the region for which it is being used (0-10 degrees).

For the 2.4 gain material, I used three polynomials (shown on the graph), the first for the range 0 <= angle <= 10 degrees; the second for the range 10 < angle <= 20 degrees; and the third is for the range 20 < angle. I read the coefficients for these polynomials directly from the trend line labels on the Excel graph for 2.4 gain.

For the 2.8 gain material, I used the same process, except that I only needed two curves (0-20 degrees and 20-55 degrees) to fit the entire data set.

The rest of the spread sheet should be pretty self explanatory. If anybody spots any bugs in this approach, or can offer any suggestions for improving it, Im happy to make modifications to it.

--Mark

 

High-Power curve fitting.zip 12.4462890625k . file
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post #568 of 583 Old 01-25-2011, 06:53 AM
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so is Flboy's calculator flawed and all the measurements we've been getting till now been wrong all along...?

Thanks,

Rana

a few funny stories from my life ------->http://www.kirtirana.blogspot.com
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post #569 of 583 Old 01-25-2011, 07:16 AM
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Quote:
Originally Posted by DrMark View Post

Hello everybody,

I was using the now well known “All Screen Gain” calculator developed by FLBoy, to compare the difference between a 2.4 gain Da-Lite High-Power screen and a 2.8 gain Da-Lite High-Power screen for my theater. It just happened that my viewing angles line up with measured points on the original gain graph published by Da-Lite (see attached). Unfortunately, the gains listed on the graph didn’t match those predicted by the spreadsheet.

After exchanging PMs with FLBoy, I found that the problem came from his attempt to provide a spreadsheet that would work for literally any screen. However, as can be seen from the Da-Lite graph, the high-power material isn’t just any screen. So, I decided to develop a customized version of the calculator that will work much more accurately for high-power screens.

I have attached my new spreadsheet to this message. You use it in much the same way as the previous calculator except that because this calculator is customized for high-power screens only, some of the previous inputs are now hard-coded into the spreadsheet.

The next posting will describe how I developed this new spreadsheet so that others can double check my work.

I want to again acknowledge FLBoy’s work on the original calculator. Without it, I never would have attempted to provide this version.

--Mark

How exactly do I open this? My CPU wont let me do it, but I am sure it is a user (me) error!

JVC 3D: Been there, done that, bought a DLP
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post #570 of 583 Old 01-25-2011, 08:29 AM
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Originally Posted by Toe View Post

How exactly do I open this? My CPU wont let me do it, but I am sure it is a user (me) error!

It's a zipped (compressed) file. You need WinZip or some other compatible software to unzip it. (WinZip is a free download.)
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