# hush box design help wanted :)



## panduro (Oct 3, 2009)

hey guys,

i have a small ht and my pj is located just behind my seating position in the sealing.
i would like to lower my noise floor and the pj is the villain, it might not be to bad, but i want it as silent as i possible can.

my pj is a jvc dila hd350. it has air intake on the front and has air exhaust on the side.

i would prefer to close the hush box completely from the ht. i can put intake and exhaust fans in the box or on wall in other room.
i have the option of making a vent or 2 to another room, but they will have to be pretty close together(max 60cm/2 feet part including pipes). im also limited to make straight pipes thought the wall so its no possible to get cold air from low position and to get the exhaust out up high. so bothe intake and exhaust have to be within 40cm/16" of the ceiling.

so questions :

1/ what fan? how much airflow do i need? max hole size is 15cm/6".
2/ do i need only fan on intake or both intake and exhaust?
3/ how much breathing room(thinking about size of box vs pj size) should i give the pj?
4/ is it nesecary to make an "exhaust" after the fan on intake and and exhaust side. or should i just go with one big box?

i hope some of you people with hush box experience can point me in the right direction 

best regards

panduro


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## gazoink (Apr 17, 2013)

panduro said:


> hey guys,
> 
> i have a small ht and my pj is located just behind my seating position in the sealing.
> i would like to lower my noise floor and the pj is the villain, it might not be to bad, but i want it as silent as i possible can.
> ...


The fan may have to be determined by experiment. You want fairly high CFM, and high static pressure, which translates to high noise unless you use a centrifugal. The airflow is unknown, hard to predict. Once constructed you can test the ambient temp in the box and adjust. 

High CFM dictates the largest hole and duct diameter possible, otherwise pressures and velocities have to go up increasing air noise. 

Placing the actual fans outside the room and ducting them to the box will help keep additional noise down. 


panduro said:


> 2/ do i need only fan on intake or both intake and exhaust?


 Dual fans help get over a pressure drop issue, but may not be required depending on the fan used.


panduro said:


> 3/ how much breathing room(thinking about size of box vs pj size) should i give the pj?


The volume of the box affects the internal temperature rise time constant, but not overall cooling. Just a guess, I'd go at least 20-30% larger than the projector.


panduro said:


> 4/ is it nesecary to make an "exhaust" after the fan on intake and and exhaust side. or should i just go with one big from I'm hush box?


 For a sealed box you want to duct both intake and exhaust out of the room.

Note that a sealed box includes an optical glass projection port, not just a hole for the lens. You need anti-reflection coated optical glass for this, not plexiglass or window glass which would degrade the image.

Once source is Edmund.

When you think "sealed box", consider than any hole at all, including cable entries, is a noise leak. Surprisingly small holes make for big sound leaks. Making a box air tight makes it sound tight too. That includes sealing all ducts/pipes to the adjacent room, and wall penetrations too. 

A little "fuzz" on the inside of the box helps keep noise transmission down a tiny bit, and you may want to put the projector on rubber to keep vibration off the box. Thick, soft, neoprene is probably best. 


panduro said:


> i hope some of you people with hush box experience can point me in the right direction
> 
> best regards
> 
> panduro


When you shop fans, look at high CFM and static pressure vs noise. Those figures track each other, so low-noise high CFM fans depend on speed, size and impeller design. Fan noise figures are a bit wild, not as standardized as you'd hope. For my last vent project I picked a fairly large high pressure/cfm centrifugal blower, far more than required, then ran it at 1/3 rated speed. Big slow fans make less noise than tiny high speed ones, and move the same air.


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## panduro (Oct 3, 2009)

hey Gazoink and thanks for you reply, it is very helpfull!

sorry for the next badly put question, with half bad english, little knowledge of heat and airflow, i cannot figure out how to write what i mean better.
so the air in from the outside fan doesn't need to be let directly into the air in on the pj, but just more or less let into the box and then the air in fan on pj will "pick" up what it needs? if so 
would that in practice mean that i could just make the air in vent exit in the back lower portion of the hush box, and the air out just over the exhaust outlet over the pj in the front? 


my biggest size hole i can make in wall is 6".
i know nothing about fans, but would something like this be adequate and do a good job in you opinion? 
http://www.ebay.co.uk/itm/L-K-PLAIN...Bottle_Warmers_Coolers_LE&hash=item1e87f305ab

thanks for the link, that will be very helpful to me. how thick should the "glass" be?

you answers do enlighten me a lot 

panduro


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## panduro (Oct 3, 2009)

Hope somebody Can enlighten me a bit ?

1: what thickness optical glas do you Think i should use?

2: as my pj Will be near Ceiling with only 10 feet to screen, i have to angle the pj downwards.
Can i keep the glas vertical or do i need to Mount it in the same angle as pj lens?

Best regards
Panduro


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