CurtPalme.com Home Theater Forum

[mookee]

hello

i need your help again please)

i need to build a "hushbox" for my floor based crt (nec 6pg plus). as i didnt came up with a better place for it than in front of the couch, so the hushbox is supposed to build something like a couch desk..

1.it is supposed to be open at the front
2. it must be of the leastest hight, so that i can use it as a propper couch desk
3. it must be as short as possible, so that....-"- without having it even closer to the wall that it allready is..
4. i dont really want to, but i could go bigger in the width..


what i am trying to say by this is that i really thought about my needs and the design..and its as good as it gets for now. it just have to work now without frying my crt.. hihi

sooo, please take a look on the attachment and may you can tell me what you think of it..ore better what you think i need to do to get it working like this..

lets see..

thank you and bw for now


lg christoph

[Tim in Phoenix]

Hello

Look at the label on your NEC for wattage of power consumption. If it uses 600 watts of power, 500+ watts of that will be given off as heat. So you probably need to push 100 cfm of air through your box or you will have a fire in no time.

[winny]

Air holds about 1 kJ/(K * m^3) so with 500 W and say 20 K increase in temperature, you are looking at 25 liter/second. Don't want to run your projector at 40 degrees ambient? 50 liter/second will half the temperature rise and so on.

Oh, and with white light being about* 300 lumen/watt and your average CRT does 300 ansi lumen, you are looking at 599 W of wasted heat.

*Depends on CRI and color temperature, but give or take.

[gjaky]

I had a similar hushbox concept on my PG xtra for a short time, it was a dead project... You really need to move a lot of air through the box (I've measured temepratures inside themachines), mine was a directly exhausted box so I ended up with a louder "hushbox" than without the box.
One note to your drawings, the general direction of moving air is opposed on the NEC, the two fans at the bottom of the machine are sucking out the hot air from inside. If you plan to use the machine on floor (like I do) set the legs for the highest position you can get to ensure the most clearance at the bottom of the machine, and you should mount small heatsinks at the bottom where the convergence and focus boards are to make heat radiation better.

[garyfritz]

Yes, gjaky is right -- the NECs pull air out the bottom. Works great for ceiling mount, less so for floor mount (since convection works against you). One popular thing to do with XGs is to tape a flat pan (like a baking pan) onto the bottom, covering the exhaust vents, and then cut a hole in the pan and attach your exhaust vent to that. You'd have to raise the projector several inches to connect the exhaust vent without too much kinking.

If you don't do that, I'd put the intake in the rear and the outflow out around the lenses. With the intake in the front like you're showing, you could end up with a dead air space (and lots of heat buildup) in the back of the box.

Either put the fan inside the box (hopefully containing the fan noise) or you could run the exhaust under the couch and hide the fan in the next room.

[the big E]

Guys its not hard to flip the fans around to pull air in from the belly mounts I did on my nec (except one) just tricky to do with the tubes in place

[gjaky]

[mookee]

why isnt it the same if i just lead enough air (50l/sec) to the place where the air is going in and do the same with the place where the air is going out without any extra ventilation anyway?

i mean, arent the vents sucking and blowing enough?

bw

[garyfritz]

The fans should move enough air, assuming the air is room-temp. If you don't get good enough air motion inside the box, you can get pooling of hot air inside the box and then the fans are pulling hot air through the chassis. The ideal situation is to entirely remove the hot air from the box. Sucking it out the belly of the projector does that. Pulling air out of the box might do that, might not.

[the big E]

[mookee]

hello again

soo, i would like to know what you think of that, beside of that its quite cool ha
(its even to scale)

do you think it works, cooler, silent, etc..?! improvements?

i thought of using 4 Thermalright TY-150 PWM Silent Fans - 150mm, which are ment to be in each hole on the front..

if you have some difficult to explain suggestions you are welcome to please use the sketchupfile.. http://we.tl/lI4MSNWTbo

[the big E]

Looks great I may do something like this for my marquee(except have the fans in the rear)as I would like to make it as quiet as possible

FYI I can't see the last two pics

[the big E]

Never mind they work now(been having internet issues)

[ecrabb]

How do you plan to arrange the fans? Intakes on bottom, exhausts on top? Intakes both on one side, exhausts on the other? Or?

My fear would be that the front half of the box would stay well-ventilated, but the "back" half of the box would pool heat - especially toward the top of the box.

To avoid that condition, you might want to put a couple of small slots on the back (top and bottom) and make all four of the fans exhausts. That should create a nice, even cross-flow from back to front, exhaust the heat and air turbulence out toward the screen, and if you designed the box with a jog in it, should be no less sound-isolating than if the box were sealed at the back.

SC

[mookee]

i must admit that i didnt really calculate the airflow in front of the box as i thought like the upper holes for in and the deeper holes for out..but thats not physics am afraid hmm

i thought about some out/in let at the backside too. guess they just must be small enough so that i dont have a additional noise outlet..


do you think i have to angle the airflow from the wholes to the pj to blockade noises from coming out of the holes?

thanks and bw christoph

[garyfritz]

Air is like water. It will flow to the easiest / shortest / least-resistance path. If you have inflow on the top fan and outflow on the bottom fan, the air will go in, make a quick u-turn, and go straight out again. Most of the box will have no airflow at all.

If you have left side in & right side out, it would be better, but you would probably still have dead air space (== heat buildup) in the back of the box.

SC's suggestion to have all fans blow out, and air intake on the back, forces the air to flush out the entire box. If you're concerned about noise coming out the back, you can build the "jog" in it like SC said. Instead of just slots on the back of the box, make the air turn a corner. Line the diversion with fiberglass and it will absorb almost all sound before it can escape out the holes. See attached pic for an example.

Be aware that all these holes, bends, etc add resistance to the airflow. Your fans won't pull their rated free-air CFM against that static resistance. You should get a remote-sensor thermometer and stick the sensor inside the CRT, near the circuit boards. See how hot it gets in there. Try it first with your projector running outside the box, like it does now, so you can tell if it got worse.

[mookee]

hi again,

am sitting now planing for a new design for the box and i actually would love to only mod my box instead of totally redesigning it..

the rear inlet with a jog seems a good and easy way to prevent heatpools..
But, first i need to know about the convection. as you can see in my sketches i planned to let in the air through the higher holes and suck it out through the lower ones... but convection laws tell me thats bulls..it.. and should be the other wayround if i dont want to suck in the blown out heat.. hmm , so, what do you think. really necessary to reinvent the whole concept?

[mookee]

thats what i came up with to avoid the convektion problem. the coloured triangles are where the air in and out can go through if i flip the fans. the triangle has 89cm2

understandable;)

bw

[mookee]

okay thats geting too wierd that way..
so the easy version, still without rear inlets until i got
one question anserded: is that an air output or input in the rearsection of the nec 6pg?

thanks too all and bw
christoph

[the big E]

May I suggest you give member tinman a pm and ask him about his fan mod and forget the box

I was going to do it on my nec 10pg but it needed repairs I never had time to fix so I parted it out trust me I think you would like the outcome