CurtPalme.com Home Theater Forum

daves123 · Joined: 16 Jan 2009 Posts: 126

I read somewhere about masking the tube faces on crt projectors for a slight improvement. Just wondering if there is anything to this, and if I should bother trying it.

perisoft · Joined: 29 Aug 2007 Posts: 2920 Location: Ithaca, NY

I guess it depends on the exact mechanism by which contrast is reduced in an air coupled lens system. If a significant part of the contrast loss is due to back-reflection between the rear lens elements and the unused white phosphor, it seems there could be a significant improvement by masking the face.

But if it's internal to the tube - between the phosphor surface and the glycol chamber's front surface, and then out to the screen - masking wouldn't make much difference at all.

And the final issue is the same as with $40 home solar panels to reduce your electric bill by 90%, and those magnets you put on your fuel lines to improve your gas mileage: If it's that easy and useful, why isn't everyone doing it? Granted, there's always the first time for something like this, but in a community of obsessed tweakers who debate the relative merits of various types of capacitors, it seems unlikely that a mod with such a large potential gain / effort ratio would have gone unplumbed.

ecrabb · Posted: Mon Jul 20, 2009 3:37 pm Post subject:

NEC put them on LC XG's, so their engineers must have seen some benefit. Question

SC

J Kildare · Joined: 28 Sep 2006 Posts: 164

I did it and when finished thought it was just a wonderful way to waste time.
Now I didn't make it real tight to the edge of the image, but could see no improvement.
I think you would get far more from even the slightest tweak to color calibration.
Jim

daves123 · Joined: 16 Jan 2009 Posts: 126

So probably just a big waste of time. I thought it might help cut down on stray light, but wasn't sure.

ecrabb · Posted: Mon Jul 20, 2009 4:43 pm Post subject:

Unless you did some pretty objective evaluation, I'm not sure with how much certainty you could say it helped or not. I'm assuming Jim, that you probably didn't go to much length to try any really objective evaluation... Of course, the point you make is valid... If you can't see the difference at a casual glance, then is it really worth it? OTOH, there are all sorts of little tweaks we do, that unless we looked at them in a direct A-B comparison, wouldn't be able to tell the difference... All those little tweaks together really add up to something, though.

I'd say there are other things you could better spend time on: Room acoustic treatments, lowering the sound floor (hush box), cleaning up cabling and improving the signal path, and even optical and mechanical setup. If you've already nailed all that stuff, though - why not?

Like I said, NEC's engineers must have seen an improvement, because as we all know, any company that kind a way to save $5 per unit certainly will. If the masks hadn't been of some benefit, they wouldn't have wasted the resources to install them.

I have other pressing issues, but I plan to install them on the G70.

SC

Zebu Fellenz · Joined: 21 Dec 2006 Posts: 2567

1031 · Joined: 22 Mar 2006 Posts: 657 Location: Finland

Tubeface masking work better on AC-machines.

ecrabb · Posted: Mon Jul 20, 2009 8:25 pm Post subject:

1031 · Joined: 22 Mar 2006 Posts: 657 Location: Finland

J Kildare · Joined: 28 Sep 2006 Posts: 164

daves123 · Joined: 16 Jan 2009 Posts: 126

So what would the benefits of masking be, potentially?

dturco · Posted: Mon Jul 20, 2009 10:37 pm Post subject:

Spanky Ham · Joined: 22 Mar 2006 Posts: 5643 Location: Comedy Central

I was going to say that I thought they were paper. I believe Guy Kuo said that putting them on the c element would help a little, but only if you have a bat cave. From this I would conclude that the ANSI cr only went up slightly.

Now as peri alluded to, the reason for LC is the light reflections are bouncing off of the c element at an angle and then hitting the tube face at reduced intesity. In an AC, the glass is flat and the reflections are hitting the tube face with more intesity. I probably didn't describe that well, but their is a picture in that 3M white paper.

I have said a couple of times that probably the best way to increase ANSI cr would be to either put a mask directly on the tube or the side of the glass facing the tube or the side of the c element facing the tube. Scott thought I was crazy when I mentioned it to him, but that is a common refrain. Smile

Mark_A_W · Posted: Tue Jul 21, 2009 2:09 am Post subject:

NEC masks are a simple paper sticker. Sometimes they stuck them on crooked or wrinkled.

And I think you are right Eric, the inside of the C element or on the Tube face directly would be better...but then the mask is inside the glycol, and you'd have to silicone on a bit of plastic or something. Way too much work to bother for me1

wallace123456 · Joined: 14 Aug 2006 Posts: 2236 Location: Northwest VA area

Other people must have liked it. I've had about 11 Sony 12xx models over the past 2 years. 3 of the projectors had tubes where they were masked. All of them, the person before me used black electrical tape on the tube face. (The tubes were shot when I got them, so I never even tried to see what the difference was.) I never tried it.

wallace

Mark_A_W · Posted: Tue Jul 21, 2009 2:55 am Post subject:

Just to be clear, the tube face Wallace is talking about is the outside of the second piece of glass.

The "tube face" Eric and I were discussing is that actual front of the bare tube - inside the glycol.

Spanky Ham · Joined: 22 Mar 2006 Posts: 5643 Location: Comedy Central

Wallace,
I think black electrical tape might be worse than nothing at all.

Mark,
I was thinking of some sort of paint at first or maybe a fabric like black velvet, but I have no idea what would hold up in glycol. If you could do a mask and cover the inside of the lens with this material, then ANSI and resolution would be maximized. I thought about trying it with my AC pj, but a LC pj would probably be easier.

Spanky Ham · Joined: 22 Mar 2006 Posts: 5643 Location: Comedy Central

Oh yeah, I tried uploading the 3M file, but it was to big. Does anyone know how to reduce a PDF file size.