A Hushbox from My LP340  

I have have started my hushbox project to silence or at least tame my LP340. The spec says 37dB, but I get 50 to 51 dB from 3 feet away sitting directly beneath it. It's finally gotten to me, and so here is my design.

I started by reviewing other member's hush boxes and gathering ideas from the resulting discussions. Next I created a poster board and wooden dowel mockup to understand the aesthetic impact on my living room ceiling. Next I drafted a model of my design in AutoCAD in preparation for building it. This past weekend, I got with a buddy and made the box out of Lexan. I still need to install the foam baffles, install the cooling fan(s), mount the box, and cover the box. I will be adding to this thread as I complete this project.

I bought a digital thermometer from RatShack to see how hot the exhaust was and to get a baseline temp. Ambient was 76 F, running was around 104 F. When I held the box over the projector, with the intake grill on, and no other holes, the temp rose to about 113 F rather quickly so I knew exhaust fans would be needed. But, the noise drop was very noticeable. The high pitched and very annoying whine was gone, so the box is going in no matter what obstacles :)

My original plan was to use a 80MM case fan to exhaust into the floor space above the projector. But I found a very promising product I think will be better. A 5.25 hard drive cooler call JustCooler TT900 from www.2cooltek.com has two 90MM fans pulling almost 80CFM at 26dB. The main exhaust fan on the LP340 is 16CFM at 27.8 dB. For $18, if it doesn't work out, then I have a PC that could use it. I also ordered SONEXmini polyester foam from the same dealer. 16"x24"x1" sheet is $9.00 so I got two. I'll update you when I get them installed.

As for the box itself, I had originally planned to paint it flat white to match the ceiling, and maybe even spray popcorn texture on it. But my wife suggested we cover it with the same velvet fabric we used on our DIY screen frame. So that's the new plan. My mom has volunteered to sew it up for me, I'll post pictures when it's ready.

Well, that's it for now....fire away :)

Here is the link to the photos thus far: Jaydmdigital Webshots

Jay

Pierre,

The plan it to use electrostatic filter material over that inlet inside the box. The dust doesn't concern me as much as the cat hair :) As for intake fans, I want to experiment with just exhaust first. 80 CFM seems like a lot to me, but I may be wrong.

Jay

Well, after two hours of measuring, cutting and sewing, my mother has completed the cover for the hushbox. The pictures are in the album now. I still need to cut the hole for the projector, paint the inside and outside of the box flat black, install the foam, install the exhaust fan, mount the box :), and install the filter and intake vent.

I'll keep you posted on progress.

Jay

Andy,

Yeah, I am very much leaning toward the optical glass route. A lot of noise comes from the front of the projector, so any openings would be bad. Another option would be to buy a bigger FLD filter and use it as my glass. Any thoughts?

I think I've decided to mount it to the ceiling first, mark the exact hole for the lens and cut once :) I might get a wild hair tonight and buy some 2x2 material for the ceiling frame. As always, I'll keep you posted.

Thanks,
Jay

Well, now they are not needed. There won't be any light from the projector exact what is projected on the screen. I'll tell her you like it, I know I'm pleased. I have some other photos of my room at Humble Home Living/Theater Room Just keep in mind that this is a living room first, and a theater at night :)

Thanks,
Jay

I understand. Actually, the CR doesn't bother me too much. As long as the blacks on the screen are equal to the "black" on the surrounding screen (in other words in scope, the top and bottom of the 4:3 screen) then black is black :)

I ordered the glass from Edmund. I may finish the whole thing this weekend.

Jay

Robster,

Logic says yes to question 1. In this manner you are flowing air into and out of the box at the same rate. I am no expert on these matters so keep that in mind :)

Question number two. The first thing to do is to calculate the total current draw. For the fan cooler I bought, the wattage is spec'd at 3.12W. Divide by 12V and we get 260mA. So I will use a wall wart transformer (I have a surplus of these things from old cordless phones etc...) rated at 300mA or greater (more is fine, but the more amperage means a bigger transformer and more heat from iron loss). Then just cut the adapter, plug, whatever off and direct wire it to your fans in parallel (ie both reds on the fan to the positive wire and the black to the other). If memory serves me, the stripe on the transformer wire is positive, but use a voltmeter to be sure, or test it with a fan...12V is nothing to worry about, you can't hurt the fan. Let me know if this is clear to you.

In my case, if the exhaust fan is not enough, then I will add another one for intake.

Jay

I have been doing some digging to understand the interaction of noise sources. I now know how dissimilar frequencies add. You use the logarithmic sum.

Combined sound level = 10 x lg ( 10^(s1/10) + 10^(s2/10) ... ) where sn is the measurement of your noise in dB.

Using this formula, and guestimating the other fans and the color wheel in the LP3x0 series, I calculated 38.5dB in free air. I used:
27.6 for the rear exhaust
*27.6 for the internal pancake fan on the bulb
*33 for the radial blower on the lamp
*38 for the color wheel
* indicates a guess

This is close to spec, so I think the numbers are correct. Just something interesting for you :) Further reading has brought up another phenomenon. If there is a flat hard surface that the noise/sound can radiate off, then another 3dB are added. I have my projector mounted about 17" from the back wall, and 3 inches from the ceiling. I'm sure there is some constructive interference going on. That calculates to 41.5dB. The meter measures 51dB at a distance of 30" or so (I'll double check that tonight).

Now, the game changes if the noises are the same dB. You need to add 3dB. So in the case of the Vantec stealth fans, two fans would result in 21 + 3 = 24dBA (A = A weighting on an SPL meter FYI). A whisper is said to be 23dBA, so no harm there :) However, if the noise/sound is in phase, then you could get a 6dB increase (a la stacking subs).

Again, just some food for thought I thought you would enjoy. I believe these equations to be correct, and I have indicated where I made guestimates. However, if anyone thinks I made some egregious errors, please let me know.

Thanks,
Jay

Robster,

12 volts is what you need to apply to get the rated CFM. If you want to experiment, I would not go below 7 volts. According to my research on the logarithmic sum of sound, the overall sound of the two fans will be 24 (for the 80mm) and 23 (for the 90mm).

I am confused by your statement about intakes. You will need some sort of hole to let fresh cool air in. My design uses a grill to cover the intake hole. The Whisperflow just has a hole cut in it. Other designs use flexible ducting that lead to a hole of some sort. so the short answer is yes, you need an intake hole. By using internal baffles of acoustic foam, I hope to eliminate any noise radiating out of the hole :)

Did this answer your question?

Jay

OK, I mounted two red oak strips to the ceiling. However, I'm not sure the best method to mount the box to these with. I want to be able to make it easy to remove the box for maintenance. Suggestions are welcome.

I posted a couple of shots of the strips at the webshots link. Jaydmdigital Webshots The strips are 1 x 2" which means .75 x 1.5" (I still don't know why they can do that).

Anyway, the original pan just called for four screws (2 on each side), but I think after a couple of removals and replacements, that the holes will get stripped maybe. Thoughts?

Thanks,
Jay

Robster,

I will soon be able to answer that question with my design, the foam should be here Friday.However, look at the Whisperflow design and the good reviews it gets. That said, if I could put in two vents (one intake, and the other outlet) I would :)

Jay

OK,

After a trip to the Home Depot, I have the mounting hardware, and the electrical supplies. I am going to use 4 brass screws into the oak strips to hold it up there. I will line the top with weather stripping. I will reroute the power to the projector receptacle through a switch I will install in the closet on the other side of my screen wall. That way, when power is one, both the fan and projector are.

I also plan to use Velcro around the top edge to hold the fabric on and allow easy removal if needed. I should finish it this weekend, stay tuned for the update and pictures :)

Jay

Jeremie,

OK, so fill me in on the details :) What did you use to "black out" the front of your box? Maybe window tint? Can you take a picture with the projector on? Any issues with using the IR remote? And very nice job I might add.

Update on my progress. The box is up! (no pictures yet) and I received the foam and fan today. I thought I could get away with a spare wall wart I had, but no dice. Apparently, the inrush current is over 420 mA. So I'm off to RatShack to find a replacement. However, I did connect the fan to a PC P/S and it was very quite. The P/S fan was louder than it was.

Thanks,
Jay

Update:

I got the power switch installed to control the fan and the projector (that was a pain). I bought some 4" aluminum ducting to put in the joist space. Mating it to the fan housing with duct tape works, sort of, but I will try to find a better solution. On top of that, the metal acts as a megaphone amplifying the small vibrations of the fan case. My wife is suggesting neoprene, so stay tuned for the results. No new pictures yet, all the work has been basic electrical. However, I did find a better wall transformer at RatShack. It's a 12V 1A for $14.99. Works perfectly. On the transformer, the striped side is negative. I just tinned both leads, soldered them together, and covered the joint with heat shrink.

Thanks,
Jay

Update:

The newest photos are posted on webshots. We have installed the SONEXmini foam, installed the fan system, and cut out the window (glass should arrive Monday). I ran some thermal tests last night. At first, the temp rose rather quickly to 140 F :eek: So I opened a hole in the bottom baffle to let some cooler air into the exhaust chamber. The temp stabilized at 110 F ;) Which I felt was ok. I still wonder if I am fooling myself about the temp though. What is a safe operating temp? Should I add an intake fan too?

As for the noise...well, with the open window (for the glass), there was a little. But for the most part, I was able to enjoy the movie at low volume. Monday should be the final installation. Look for the update.

Thanks,
Jay

One question, is the hole covered too? It looks that way from the photos, but hard to tell for sure.

I agree, the FLD is a requirement for my PJ.

[quote]I would like to get some screen shots but the room is too dark for the pics and they turn out very poorly. So until I can get the picture to turn out as good as what it really looks like I am not going to post any pics.[quote]

I have had to use a Gamma correction of 1.66 to 1.77 for all of my pictures I have taken thus far. Some required even more. But I understand.

So I assume that is once in a blue moon :)

OK, have you taken any temperature measurements of the exhaust out of the back of the PJ? I want confirmation that 140 F is normal. Otherwise, I need to add more fans.

Thanks,
Jay

Update:

I ran another thermal test this morning with out the box. On the right side (facing the projector) about an inch back I measure 155 F. This is the side with the bulb. On the other side, I only measure 120 F at the same distance. therefore, if the temp is only 140 F with the box, then I think I'm fine. In fact, I may use my wife's design after all.

Jay

Update:

I attached the fabric cover last night. I painted the intake vent flat black. I have asked Wendy to make another vent stack (like the one on the webshots) tonight, and the glass is supposed to be here today. If it is, then this project will be over tonight.

Thanks for the feedback, and I hope others will get ideas from how we did it. If anything is unclear free to ask.

Thanks,
Jay :cool:

Update:

It's finished!!!!!!! And it is SILENT. The ceiling fan makes more noise. I have to look for the light in the lens to know it's on.

However, it was a bit of a rough day. Edmund took my address down wrong, so FedEx could deliver. I left my tracking number at work, so I had to get a control number from the operator to claim my package. The glass is way over packed (if any of you were wondering) and coated with a blue film. The directions say use a piece of 2" wide tape to remove the film...nope. More like use your fingernail to peel an edge and then slowly and carefully pull the film off. Wow, the glass is invisible! OK, now to mount it. Get out the Dap Clear caulk. Hmmm...do I put it on the glass or the box....ok glass....DOH! the caulk was warm,runny, and spurted right onto the middle. :eek: OK, I grab the lens tissue that it shipped in to get the silicone off quick. AHHHH!!! now there is a huge smudge! :( OK, don't panic, use isopropyl alcohol and some more lens cloth. Oh yeah that worked...NOT :rolleyes:, now the whole glass is either spotted or smudged. I called up Wolf Camera, they say they can help :). Quick trip and bingo, almost as good as new.

Maybe you will learn from that mistake. In any event, it's up, it's done, and the living room is back to normal. I hope you enjoyed reading and seeing this project. I will post the final photos tomorrow morning.

Thanks,
Jay