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Discussion Starter · #1 ·
Every since I bought that first xg135, I've been using my homebuilt, plywood hushbox...it's huge, heavy, and has sharp edges and corners. Not the best thing for sound, especially when it's hanging above your head.

I'm starting to gather a plan in my head for a new hushbox.

This one will be smaller, and can only be used with the plastic covers off the XG, it will be much lighter as I'm going to make it out of fiberglass.

The plan so far is this:

1)I'll install all the outer panels and take the pj from the ceiling.

2)I'll "fit" 1.5 inch styrofoam all around the pj and extending to the floor (as pj sits on the floor)...this styrofoam will give me a hushbox mold that I can lay the glass on.

Once it's cured I can remove the styrofoam and pj's outer covers.

I will then have an inch of space for sound absorbant material.

I'm thinking these fans run in the 800 to 1200 hz range, do any of you know of a good sound material that works especially well in that range?
 

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That will be quite a bit tighter than usual for a hushbox. Typically you aim for 3 to 4 inches of free air space on all dimensions. That's not including the additional space taken up by the acoustic insulation. The fiberglass molding idea should let you do some pretty neat curves and features. Next you'll be doing molds for your own Lambo.
 

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Discussion Starter · #3 ·
Yes, I had a corvette once that I brought back from the dead, so that's where I started using fiberglass.

I have my remote sensor thermometer in the tube cavity of the pj, so if this H-box ends up being to small I will know it immediately by the temp rise...however the evac system I've made uses a fan that flows 70 cfm.

Even if you were to loose 10 cfm because of ducting that's still 60 cfm, the H-box is approx 11 cu. ft., the pj takes up a good 4 or 5 cu. ft.fm, so that leaves, at worst case 6 cu. ft. this means the air in the H-box's air should turn over 10 times per minute.

With a pull like that, and all the pj's fans running, it should be no problem, even with only an inch-and-a-half around the pj. Removing the plastic covers will give me an extra inch or so.

However, by making the H-box smaller, this limits the thickness of my sound absorber, so it becomes critical to get something that works well in the correct freq range.
 

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Have you thought about corregated plastic? You can make a box, glue whatever foam you want to the sides and it will only weigh a few pounds. You can rivet latches on it to. Comes in different colors to. Very strong material.

Ask a packaging company near you about it.
 

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Discussion Starter · #5 ·
No, I've never heard of corregated plastic...but, I will check into this. The idea of rounded corners and edges is what has drawn me to the idea of fiberglass. Can this corregated plastic be molded in such ways?
 

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How about blue or orange tinted lucite kind of a IMac look. :) Oh yea, to pull it off right you need to leave your XG in the nude.


Mike
 

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Discussion Starter · #7 ·
That's no problem, my XG is kind of an exhibitionist anyway...it's always showin' something :)


Unfortunately, with the covers off, mine doesn't look as good as most of them, I've done alot of ductape work to increase the efficiency of the fan system.
 

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I have a suggestion. Use foam of the thickness desired and put a release material (aluminum foil) over it before you lay the glass and resin. I have done this with fiberglass before and it leaves nice rounded corners and will follow contours real good.


Deron
 

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Now I have a question.


If you build a hushbox and project through a piece of glass, does this do anything to the brightness or picture and would you want to use optical quality glass? Or should you design the box so the lenses protrude?


Deron
 

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Deron,

The foam idea sounds like a good one. It could really keep the weight down and provide excellent sound damping. I have an inboard ski boat and the motor cover is made that way. It really eliminates the engine noise.


Kenny,

The biggest thing about working with fiberglass is the fumes. You know that already if you rebuild a Corvette. I rebuilt a Corvette when I was 19 and still have it I'm now 44. I think it killed a couple of brain cells along the way or maybe that was the eighties. Anyway better work on it outside and wear a mask or the fumes and your wife will kill you. I would think you could make a wood frame lined with foam, lay in the inside layer of glass allow to cure, remove the frame from the outside, shape the corners and edges of the foam then lay the outside layer of glass. Then apply gelcoat to get rid of the fiberglass grain. You also could use bondo but it would not look as good before painting and besides gelcoat is easier to sand smooth. It might also be a good idea to use wood stringers where the hinges and latch are mounted to give it a little more rigidity. I have to build a hush box for my projector also and your getting me fired up about this project and hey, if you sell your projector you can always go fishing in your hush box. :)


Mike
 

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Way to go Kenny. Your projector must not need tweaking any more. A while back on the DILA forum there was a hushbox built with a very good foam that was an inch or less if I recall. He had the links to the vendor on that thread. Not sure if you searched the dila forum for it yet....
 

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Discussion Starter · #12 ·
Yes, as I start to draw this out, I will be using the 1.5" styrofoam as a mold, then as Deron suggested tin foil as a release material, and a 1/2X1" hardwood frame at the top for hinge and latch mounting.

As far as the glass over the lenses, I've read of people that have done that, but a certain amount of light will be reflected back into the lenses, which also means less light at the screen...doesn't seem like a good idea. Others have mentioned having glass over the lenses and the Hbox completely sealed, no other means of pulling air into the box, that's gotta create a heat problem.

My box will be built so the opening is just out past the end of the lenses, and 1/2" larger than lens area...that's the easy way...

I have also thought about building the box so the front actually bolted on and off...once the box was raised and latched into place the front would be held in place by studs and wingnuts, that way the Hbox front piece could be built to a tight lens tolerence and a round rubber boot used to "fit" the lenses snuggly into the holes. Lastly I'd build the air inlets with a sound baffling maze. This would cut the most noise, and is still an option...I'm doing alot of thinking here. (you can smell the brain cells burn)


The only problem with the bolt-on front is once I sell the pj, I can't use it as a boat for fishing :)
 

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Quote:
Originally posted by KennyG
No, I've never heard of corregated plastic...but, I will check into this. The idea of rounded corners and edges is what has drawn me to the idea of fiberglass. Can this corregated plastic be molded in such ways?


Corregated plastic comes in a 4 x 8 sheet( and I suppose other sizes. and looks like double wall cardboard. It was designed to eliminate wood crating, and be rusable and recycleable.

You can bend it, cut it, glue it etc any way you want. It would make a neat corner in box form. . It's super strong, you can't tear it or rip it. It can be bent forming a rounded corner to. If all fails, I can put you in touch with my local supplier.
 

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Does anyone sell them pre-made with Kenny's idea in mind?


i have the same pj and i'm looking for something like kenny has in mine but want to buy it already made. no time to make one.


sugestions?


thanks

carlos
 

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Discussion Starter · #15 ·
Sam I want to thank you for the corregated plastic idea, I bought two 4X8 sheets of it today. It is very thin, I was hoping it came in different thinknesses, but it doesn't seem to. Not to worry, I will be bonding two layers of it together, running the corregation at 90degree angles for strength.

I've decided to go all out with this one, and design it with a removable front so I can make the lens fittings tight. The bottom of the box will have two bottoms, space 1.5 inches apart, the back open to the room, and front open into the box. So the Hbox vent fan will pull air from the back of the Hbox, along the bottom of the box, then at the front of the Hbox the fresh air will empty into the projector cavity and be pulled to the suction at the back of the Hbox cavity.

Should be alot quieter than the Hbox I'm using now.
 

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Where did you get this corregated plastic stuff ? I think I might know what it is, but I don't have any idea where you would get it. Also is it paintable ? If you could take a few shots of the construction while in process that would be great.


Thanks

Mike
 

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Discussion Starter · #17 ·
This stuff is just like a cardboard box used for shipping, except it's made out of plastic...two layers with a "corregated layer seperating them. The stuff I bought is the same thickness as it's coardboard counterpart. (about 1/4")

I bought two 4X8 sheets @ $13 each.

I have since gone to Lowe's and bought 1.125" cornerbead wood, lattice strips at the same width and depth, and small steel corner & "L" brackets. these brackets will be bonded to corners.

Then the corregated plastic will be bonded on both sides of the woodframe...inner skin's grain running one direction, outer skin's the other.

The front will bolt on using the cornerbead of the box structure with bolts bonded & gusseted...rubber seals around the lenses.

This design leaves a 1/4 air gap between the inner & outer plastic skins...........Can anyone recommend a good insulator for that gap? Then, perhaps a 1" thick sound absorber that works best in the 1khz range, for the inside.

Thanks for the thoughts on this.

Kenny
 

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Discussion Starter · #18 ·
Mike, I wish I could get some shots, but I don't have any way to do it. I don't have a scanner or any thing to get the pictures into my computer, sorry. I also realized you ask where I got the plastic and I didn't answer...I found a place in the phone book under "plastic", they make various item out of every type of plastic and acrylic, so they had this in stock.

I also picked up an incredible adhesive at Lowe's call "GOOP", I bought their "marine" application. This stuff sticks to ANYTHING.

Between that stuff, wood glue and #4 1/2 screws this Hbox will be strong and light...looks like about 15lbs.

I'm building the front of the Hbox in two pieces, the lower will be part of the Hbox, and when the Hbox is latched in place, it will surround the lower half of the tubes, then the upper piece will screw on and seal the upper half. (studs & wingnuts)
 

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Discussion Starter · #19 ·
I've been away from the forum over the last few days finishing this box...it comes in at about 20 lbs, which is great, the last one was hard to lift using both hands (and arms and legs!) This one can be lifted by one arm.

The inrush of the evac system is much quiter, but the sound of the pj is still about the same as the old box, about 9 db down from open air...I must find a good, light sound absorbing material.

Since all the air is pulled from the back of the Hbox, through a 26X2" slot, I'm building a filtration system using furnace filters cut to fit a 26X4" plenum mounted to the back.

It was nice to watch a movie tonight that didn't have the pj screaming in the background (foreground?)
 

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Thanks for the tip on the plastic. I missed it before. The hush box sounds good. (pun intended) I saw Guy used a couple layers of fiberglass insolated ceiling tiles in his hush box I don't know if that is option for you. Did you put any kind of temperature sensor in the evac system or is it on all the time? It does however sound like that hush box will not be much of a fishing boat.:)


Mike
 
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