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
[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
