glassing MDF enclosure

[ncc74656 2]

I was thrown into the fire so to speak at work, designing and building a box for 2 phenox gold 12" subs and i found out our company policy today is to resin the entire inner box and glass the corners. I do not believe i have enough resin to coat the entire box so my question is this:

does covering the box with resin or any section of the box improve its performance? should the corners be glassed and if so what is the best way to do this? i was shown a corner piece with resin and kitty hair pressed into it, it was not smoothed.

i need to finish the box tomorrow.

Edited April 13, 2014 by ncc74656

[SpeakerBoy 64]

I've heard resin alone can actually weaken the wood, it's not the same as actually fiberglassing the whole interior.

[Tirefryr 1,742]

What kind of policy is that?    Some SPL competitors have had gains by painting the interior with resin, but just in the corners and not smoothed is going to do nothing.  Stupid policy.

[SacredTanakh 67]

I've heard resin alone can actually weaken the wood, it's not the same as actually fiberglassing the whole interior.

No..

[///M5 2,833]

and your idiotic owners strike again....at this point i dont think they have said somethi g correct yet

[jcarter1885 995]

Find a new shop to work at.

[SpeakerBoy 64]

I've heard resin alone can actually weaken the wood, it's not the same as actually fiberglassing the whole interior.

No..

Never glassed anything myself, but I've read that here on the board a handful of times.

[ncc74656 2]

my first thought when i saw the "demo" piece was that it would only work for a sealed box or MAYBE the outside corners of the chamber, farthest from the port. the sample was a single corner cross sectional piece cut from a box so it had a bottom and 2 sides. the inside wood was coated in resin and then there were pools of resin with kitty hair mixed in around all the corners and seams. im certain this is a poor idea for any place there is air flow but if done properly and smoothed out would it provide any real world benefit in this application? given that this is not a project for myself i want to be damn sure that i do everything i can to make this box right for the client.

the box is holding 2 12" 1600W 30mm Xmax (one way) subs. The other reasoning for putting resin on the box was to seal the wood from air escaping. now my first thought was the gaps (if any) between joints. this box does not have gaps as an actual table saw was used, however it was then explained that this is to prevent the WOOD itself from air flow. in other words MDF breaths. when i questioned this i was told that if you use a vacuum to lift 4X8 sheets you can lift 2 or 3 sheets through one another with a single vacuum plate. now even IF this is true i would expect the 2.5X12" hole in the box (other wise known as a port) to allow the pressure to escape FAR before the wood would ever breath to this extent?

what are your thoughts on all this?

[Quentin Jarrell 671]

Yes vacuum will go through MDF.  My vacuum form guy uses MDF bucks and he gets vacuum through 4 or 5 sheets thick without drilling holes in it.  

[ncc74656 2]

ok so the wood does breath. what i take away from that is that if i am building a sealed box for something with high power i would want to glass the inside of it but for a ported enclosure i am unsure if it would make a difference. a direct vacuum plate is a totally different thing from a speaker shoving air along its surface and out a port. i could perhaps see letting resin pool at the bottom of the port to create a rounded area for the air to flow across?

[Julian 641]

For spl instances it's a go to tool for gains. Also the only time we ever glassed the inside of the box was by customer request or for marine applications.

[Impious 1,476]

Yes MDF is porous. However for the average daily user the affect is negligible and the time and cost of the resin is completely unnecessary for what is an otherwise unnoticeable difference in performance. By the way most enclosure programs can include leakage losses (Ql) in the response calculations....so the leakage loss of the wood, assuming a reasonable value is used for Ql, is already accounted for in the design of the enclosure.

[ncc74656 2]

i use torres most of hte time for box size calcs when a manufacturer has fairly specific specs for cubic, port area, and tuning. if they dont then i use bass box pro and winisd to model things and try to get an idea of how it will respond. id assume both of these programs have such Ql calculations but i will have to check.

for this box i think i will silicone the seams on the inside nad perhaps add some 45 degree cuts to the inside of the port. the work and cost of glassing the inside does not appear to be worth it.

[ncc74656 2]

a second question, i have always used screws with pre drilled holes to put boxes together (along with glue of course) and while i understand the glue'd joints become stronger than the wood itself i assumed the screws did aid in the rigidity of the box or at the very least helped build a solid seal with teh glue. I was told that the screws are worthless in box construction and to just use a nail gun to assemble pieces. any input on this?

[///M5 2,833]

Screws, clamps, nails any are fine which doesn't matter.  Just need to have good pressure on the glue joint.

[ncc74656 2]

kool, well that pretty much answers that. my challenge tomorrow will be to cut perfect circles with out a router table for the baffle.

[///M5 2,833]

kool, well that pretty much answers that. my challenge tomorrow will be to cut perfect circles with out a router table for the baffle.

Challenge? Don't you have a circle jig?

[SpeakerBoy 64]

Your shop doesn't have tools?

[swift 501]

Alot of car audio shops are setup that way. I know here my buddy managed one and his install guys had their own tools and section of the shop. They may have even rented their bays kinda like at how barbers just rent the chairs and have their own loyal customers. 

[Lee Carter 150]

I plan to  resin my box- purely to put automotive grade paint in the port.  And since I am doing the port- may as well do it all.  i also want to keep the wood smell down.  The box I built for my Suzuki still make the truck smell like wood(after you pound on it for a bit) after 6 months. 

[Quentin Jarrell 671]

I plan to resin my box- purely to put automotive grade paint in the port. And since I am doing the port- may as well do it all. i also want to keep the wood smell down. The box I built for my Suzuki still make the truck smell like wood(after you pound on it for a bit) after 6 months.

Don't. Use an automotive grade primer. Do NOT use resin.

[Lee Carter 150]

Roger that- we were going to discuss it.  Thanks!

[stevemead08 752]

For spl... Yes resin it and smooth corners. Sand smooth to glass like finish.

For a daily system, I wouldn't bother.

[SacredTanakh 67]

I plan to  resin my box- purely to put automotive grade paint in the port.  And since I am doing the port- may as well do it all.  i also want to keep the wood smell down.  The box I built for my Suzuki still make the truck smell like wood(after you pound on it for a bit) after 6 months. 

haha what? resin it so that you don't get the smell of wood? the smell of resin stays in the car a very very long time, and I think wood is a little more pleasant of an aroma.

That being said either way you can get a very smooth nice looking enclosure. I prefer resin on all my enclosures though to seal everything up tight.

[ncc74656 2]

my boss had a circle jig for his router so yes, we do have one. i had gone searching to find one but no hardware store i went to had ever heard of such a thing so i was just going to try and use a jig saw. the box is nearly complete... crazy long build as i had to run to the store to buy tools neither i nor the shop had, yesterday the shop ran out of glue, today the shop ran out of screws... just lots of hickups. in either case i have the box with in 1/16 of an inch of error on the cuts so its coming together very nicely.

i am using some 45's striped across the inside of hte bottom of hte port and then silicone on the rest of the seams. not using any resin. here is a pic of the design:

http://i.imgur.com/XXKM1iq.jpg