Is plywood safe for indoor use?

If you want to stop noise getting out you will need a lot more than a sheet of plain ply wood because if the structure is too light it will just act as a resonator. You will need something quite heavy like thick (I'm talking 30 mm+) timber probably a double layer of 18 mm ply or MDF with a layer of something able to absorb noise in between. You could line the inside with carpet but that will muffle the sounds inside the box (presumably you want to make music inside the box?) You will also need the same on the floor.

BTW I reckon your biggest risk by far associated with this project will be the drive to the hardware store to pick up the timber.

Skip the crude ply box. How shabby. Think outside the box.
Noise-cancelling hearing protectors have nearly been perfected
for the trap/skeet shooting sports. No fooling, they really do work.
6 x 10^9 trap shells were sold in the USA alone in 2010.

I still use my 'muffs from my Unlimited Handgun IHMSA days
7mm/.308 full length cartridge in a pistol is a handful.

I tell ya, some days, that silence is very nearly priceless.
No, I don't know where my ex lives.

Quote:

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Originally Posted by Robson Valley

Skip the crude ply box. How shabby. Think outside the box.
Noise-cancelling hearing protectors . . . .

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I think he wants to make a noise inside the box and stop it getting out - not stop noise getting in.

Hmmm.... ventilation? Farting? You are a fruit loop mate! I think I may need to build one too!!!!!!:C

like ...

why does the OP need a box at all ?
making a box sound proof requires a minimum of 6 sides which in turn requires the box be ventilated
An open front box will just bounce sound arround
and if the generated noise is loud enough it will be transmitted through the walls and floor of the room


for this assignment, I think the OP needs to provide a bit more detail of what will be going on inside the box and why shutting the door to the room is not enough