Im picking up a sub box that will go perfect with my SPLX 12" (Had a DD9512) it's listed in the for sale section.

Im wanting to no what to use as a window on the back of the box. Being an SPL box i would think it would need to be strong and so and so thick.

Im thinking of cutting a rectangular hole a sertain thickness and lay the perspex or glass over it and ovcoarse being bigger than the hole i cut out.

Other than what material i need to use what would be the best way to seal it so no air leaks out. Was thinking of running a bead of silicon on the inside were the hole i cut meets the perspex (Just put my hand in thrue the sub cutout and seal it)

Any help would be great as i can't afford a custom box at the moment so thats why im doing it to this pre built box (For $50 it's better than a small box you buy from strathfield etc)

Use glass, wont flex as much as perspex, and use sellys glass silicone to attach and seal it

What so i don't screw the glass in or anything? How thick does the glass need to be?

As thick as you can afford, the thicker the better

so if he only afford 2mm thick glass, thats ok?

Ok then and wouldn't i use more than just sellys glass silicone to attach it or is that stuff super strong lol.

well, perhaps the logic is if you attach it from the inside, the pressure caused by the woofer in the actual box will keep it 'in place' and the silicon is there to give it the airtight seal needed?

I reacon that thick perspex will flex so minutely, it would not be an issue at all (10mm and up). The actual wood would probably flex more than the perspex itself.

no need for screws, the silicone is really strong, its actually acidic and really holds onto the glass, try to use about 8-10 mm glass

Yes but as i said at the start the box is already made im buying it off the forums second hand for $50 until i get the money for a custom job. But in the meantime i wouldn't mind a bit of bling thus the idea of a window. I'd have to pull the box apart to do it from the inside unless i can unscrew the back panel put it on and some how seal it all up air tight again(But i would rather leave that as a last resort). And if perspex will work id rather use that as i can seal it and screw it in as it is on the outside and it will pop off at high volume ovcoarse without being screwed in.

When i get the box i'll do some measurements and go source some thick perspex locally.

I got another idea on how to do it will do a google sketchup image as it's easier than explaining.

As shown in the images i was thinking of putting another layer of wood on the back of the box and have it's hole about an inch bigger all round and have the perspex recessed into that hole and screw it into the first layer and use foam strips behind it to seal it or just silicon.

if you go perspex you'll have to use about 25mm to have the same strength as 10mm glass

Will be perfect if i can get some 25mm mdf thrue school.

25mm plexi? You have to be joking, right? I mean thats ridiculously thick, especially when the rest of the box is made from 16 or 19mm mdf.

I personally think that is overkill to the extreme, but I could be wrong, I have been before.

Could be as the box is ported i don't think there will be as much pressure as a sealed box. I'll get the same thickness as the box and if it is to thin i can just redo it and use the perspex elsewere

yes, for a tweeter enclosure lol.......

lol, id say the mdf is under kill if its only 16-19mm. especially considering most people here are using at least 20mm with the majority probably 25mm. Personally 32mm for me =D.