AVS Forum banner
1 - 7 of 7 Posts

·
Registered
Joined
·
423 Posts
Discussion Starter · #1 ·
NEC XG COFFEE TABLE








[click thumbnails for larges images. This is also posted here. If anyone can send me code to line up thumbnails in a row, I will edit. Thanks!]

DESIGN GOAL AND RESULTS:
Compact - Yes. Outer dimensions are 22" high by 28" wide by 36 1/2" deep. Active cooling eliminates the needs for extra space so a very tight fit around the PJ is possible.


Quiet - Yes. Outer layer of 3/4 oak veneer plywood - lined with 1/8 inch heavy sound blocking vinyl - plus inner fill of 1 inch sound blocking material really silences the PJ - Placement and limited opening of the airflow porting areas means little noise escaping overall an no noise escaping to the critical rear and sides.


Cool - Yes. The fans draw air directly through the core of the PJ -around the heat generating tubes. The temp probe placed in the center of the PJ, right near the green tube, typically reads around 100 degrees (in my 75 degree room) while open air use reads around 110 degrees.






DESIGN PRINCIPLE:
Room air is drawn in through the front of the projector (between and around the lenses - the INTAKE). The air moves through the projector---which is housed in an upper chamber - to the back of the projector. Then the air reverses direction - it makes a 180 degree turn down into the lower chamber and moves forward to be expelled in the lower front - the EXHAUST. Air movement is driven by two banks of fans; 4 fans in the back of the lower chamber and 4 fans in the front of the lower chamber.


This picture (crudely) shows the direction of airflow


(Note: Neither the fans nor acoustic materials - which help separate and seal the chambers - are shown here - see next series of photos).

DESIGN:
These pics show the elements of the lower chamber:


The platform on bolt "legs"


The fans set into 1 inch foam material (303)


View of Rear


View of front next to outer shell


Fisheye view of lower chamber (Note: side panel of foam is removed to take the pic; the power adapters don't take up as much room as the pic suggests)



Final Assembly Pics:


The vinly-lined shell being placed over the platform


The small amount of spacing left for the air to flow front from the top chamber to the lower chamber


Foam being dropped into the sides (to help seal the chamber and absorb sound)


Foam on the sides blocks air from going astray.

Notice that the width of the box itself is just about 27" (The top with the overhang extends another 1/2" or so on each side to 28")

The distance from the outside of the box to the NEC frame is around 2 inches - with just under 2 inches of material on each side of the NEC frame. (To each side is the (not quite) 3/4" oak plywood, the 1/8" vinyl and the 1" of drop-in foam.)


Inverted top (Note the crudely routered craters - these allow for the lowest possible projector height, by thinning the top where the PJ is tallest)

CONSTRUCTION:
Basic assembly of shell



Railing routered at 45 degree angles


Dowel Assembly


Completed Shell

IMPORTANT PARTS AND MATERIALS:
*1 inch sound absorbing foam

*1/8" sound blocking vinyl material

* Quality fans and transformers to run fans at lower than rated fan voltage

Note: These quiet-design fans are run at 9V or 6V for even quieter operation. (I probably didn't need that many transformers, but I wasn't sure of the amperage and they came cheap from a PC recycler.)









PROTOTYPES, EARY VERSIONS AND REJECTED DESIGNS:
I really liked the model with the side fans - (foam around lenses give it a nice look). This had intake holes on the back - Unfortunately, the air flow pattern bypassed the PJ core where it was needed most. Another penalty was width - the working design is a good few inches narrower. The last pic also shows an earlier working version that was unnecessarily wide












FAQS:
Q. Isn't the hot air being recycled back into the projector again?

A. Likely some of it is, but this still works, I guess, because a much larger percentage of hot air simply dissipated into the surrounding air, and the air being sucked in is always cooler than the air being expelled.


Q. More about the temperature performance?

A. Temperature inside the PJ stays pretty consistent at ambient room temp +20 to 25. With room temps at around 75 to 80, the internal temp will get up to around 100. This is about 5 to 10 degrees cooler than the PJ sitting out by itself. Measurements taken at a variety of locations within the PJ remain pretty consistent. Its seems as if the air movement prevents pockets from building up. My "reference" sensor is kept at the focus coil thumbnail screw at all times.


I should note that with the fans running at higher speeds (with somewhat increased noise), the temps can be reduced further. I've attached another archive photos showing temps around 90 degrees throughout the PJ. If I remember correctly, this was an earlier version that was wider, but the fans were running faster too. I'm pretty sure it was fan speed more than internal volume that brought temps down so low (and this would seem to make sense), but I'm not 100% sure.


Earlier version of PJ - fans running at higher voltage (in a wider enclosure)


Q. More about Noise?

A. Noise is dramtically reduced. While the PJ/box isn't dead silent, it is is quiet enough to be almost unnoticeable with virtually any sound playing or with slight background noise from outdoors. Even in a totally silent room it barely calls attention to itself.

REFERENCES AND CREDITS:
KennyG, Iceman, Aksor and others are credited with so much of the basic design ideas.

Sound Dampening Plants

Best Hushbox Material

Hushbox Question

Guy Kuo Hushbox

Hushbox 21st Century

CRT Hushbox with Glass Front

The Aksor Coffee Table (and many others)

Coffee Tables
 

·
Registered
Joined
·
8,079 Posts
Wow.


Nice box.


Well documented.



What did you do with the stock NEC side fans? Are they obstructed by the foam?
 

·
Registered
Joined
·
423 Posts
Discussion Starter · #3 ·
Thanks for the vote of confidence.

Quote:
Originally Posted by Mark_A_W /forum/post/15479750


What did you do with the stock NEC side fans? Are they obstructed by the foam?

That's probably a more pertinent question than the ones I surmised.

I considered removing them or at least disconnecting them. But then I read somewhere that the PJ has some type of intelligent fan monitoring and might not function properly with the fans disconnected (although some clever forum members have suggested there would be dummy loads or other ways to "placate" the fan leads.). I probably didn't have the guts to risk damaging anything.


With this contraption, the NEC's fan currents are mostly over-taken by the the 8 fans moving air through the projector. You can actually feel a light vacuum type suction around the lenses - it's noticeably more powerful than what you can feel near the PJ's own fans. The foam does not stop the NEC's own fan blades - as long as it isn't packed too tightly. This does leave room for improvement - Defeat the NEC's own fans and maybe the PJ would be quieter.


As a final note, there is one internal fan in the XG that really whizzes - the most annoying of them all - yet this one blows towards? some critical heatsinks so I guess its still effectively helping cool something.



PS

I did sell the PJ recently. This posting had been outstanding for a while, but the disassembly of the box was a good (and the last) chance for me to take the right photos and post this project.
 

·
Registered
Joined
·
5,876 Posts
Nice work. Glad to see you around.
 

·
Registered
Joined
·
154 Posts
Nice Job I'm glad I inspired you. As for mine I eneded up selling it when I sold the projector. The buyer liked it too much.
 

·
Registered
Joined
·
2,284 Posts
DJordan


Do you have low ceilings?


From the pics and the posting it is quite obvious that you have put a great deal of thought and time in the design of this hushbox!


Prototyping! hehe...I can say that I ever do...I have a habit of cutting first and then measuring. (...but it works out most of the time!)


Very nice and well documented post


Two thumbs up



Martin
 
1 - 7 of 7 Posts
Top