Sealing the inside of an enclosure

[NyxOne]

How important is it ?

I know some of know do it and some don't (like me). I'd just like to have your input on what benefits, acoustically, can be gained by sealing the inside of an enclosure? It there any ?

If you do it, could you share your favorite Technic/method ?

Thanks,
Chuck

[johnnyrichards]

Straight cuts and lots of glue seal the joints. Sometimes I spray the interior with rubberized undercoating, sometimes just primer. Sometimes nothing at all. Someday I might try Rhino lining the inside just for kicks.

[Steve Henry]

Being a novice woodworker, I have taken several classes at Woodcraft & Rockler. I posed this question & in both instances with different instructors, do the same to the inside as you do to the outside. According to them, this makes the rate of expansion the same for both sides & both directions. With glue sealing & painting, this is a no brainer, but when I asked about veneering, they said even more so. They recommended using the cheapest veneer you had around for the unseen areas of any project. Again, their opinion.

[NyxOne]

Straight cuts and lots of glue seal the joints. Sometimes I spray the interior with rubberized undercoating, sometimes just primer. Sometimes nothing at all. Someday I might try Rhino lining the inside just for kicks.

So what you're saying is that you seal your inside depending on your mood ? By the way, what is "Rubberized undercoating" ? Do you use any specific product ?

Being a novice woodworker, I have taken several classes at Woodcraft & Rockler. I posed this question & in both instances with different instructors, do the same to the inside as you do to the outside. According to them, this makes the rate of expansion the same for both sides & both directions. With glue sealing & painting, this is a no brainer, but when I asked about veneering, they said even more so. They recommended using the cheapest veneer you had around for the unseen areas of any project. Again, their opinion.

That's an interesting point of view but I don't think I'll ever veneer the inside of a speaker!!! Way too expensive! LOL!

Yesterday I've used a mix of 50/50 glue/water to seal the inside and outside of my latest enclosure and then sanded it with 220 grit. It really does a good job so I think I'll stick with that method until I find something better or easier (if that's possible)

Thanks for your inputs guys and sorry the late reply! (Better late then never they say)

Chuck

[johnnyrichards]

So what you're saying is that you seal your inside depending on your mood ? By the way, what is "Rubberized undercoating" ? Do you use any specific product ?

Pretty much lol, I have heard tales of MDF and particle board and plywood being porous but I don't think it matters one iota even if it is. I mean I have built a small, sealed subwoofer with fairly high output using unfinished 3/4" particle board and never heard any whistling from air leakage through the walls of the enclosure. So yeah, depending on my mood I will do something to the interior

I use this one.

[Dirttracker73]

As recommended by someone else in an older thread, sanding sealer works well. It seems to penetrate the MDF and sands to a smooth shiny surface that builds up with multiple coats. On the other hand, it does stink of solvent so if you are working indoors it may be an issue. When dry it is fairly water repellant, more so than the wood glue I compared it with. After all, sanding sealer is for this purpose.

[evilskillit]

Depends on what you mean by "sealing" I'll run a bead of caulk around the inside of all the corners and smooth it with my finger. It looks nice and helps me sleep at night, whether it does anything else I have no clue. As for any other type of sealing, well most of those surfaces are covered in some kind of adhesive and sound damping so there isn't much point in doing anything else to them, I think.

[Æ]

How important is it ?

I know some of know do it and some don't (like me). I'd just like to have your input on what benefits, acoustically, can be gained by sealing the inside of an enclosure? It there any ?

If you do it, could you share your favorite Technic/method ?

Thanks,
Chuck

I don't find any need to seal the inside of an enclosure. Of course I don't want any air leaks so I make all joints and seams air tight with liberal amounts of glue.
I did build a pair of enclosures out of pre-veneered MDF and the veneer was already applied to both sides of the MDF, I imagine for uniform contraction and expansion. But I wasn't going to stain the insides of the enclosures.

[hulan]

I never had problems and all I do is a bead of silicone on the inside seams.
Perhaps I'll try the sanding sealer in my next project after I finish these little ones I'm working on. Thanks for all the insight guys.

[marscoast]

I slather a coat of Bin shallac-based primer on the inside. It's cheap and easy. Like many others, I seal the seams with a bead of silicone.

[fastbike1]

A speaker is different from a piece of hardwood furniture. The MDF or Plywood aren't going to be subject to much "differential expansion".
Sealing the seams makes sense from an acoustic perspective. Finishing the inside of the cab, particularly verneering is a waste of time.

I never had problems and all I do is a bead of silicone on the inside seams.
Perhaps I'll try the sanding sealer in my next project after I finish these little ones I'm working on. Thanks for all the insight guys.

[SpacePatrolman]

I've never heard of sealing the surface of the material used for an enclosure. As others have mentioned already, I don't believe there are any advantages to doing so.

Though for the speakers I have built, I have run a bead of silicone caulk over the interior seams to seal any possible voids in the glue used to join the various panels. While probably not 100% required, this is a cheap-n-quick thing to do, so not a problem for me & adds a little peace of mind.

As far as the expansion issue, I've owned several sets of commercial speakers that were/are 30+ years old and besides the normal scratches on the veneer, the cabinets themselves were in perfect shape. These included enclosures with real & vinyl veneers and enclosures built with particle board and enclosures of plywood.

[skatz]

I generally run a bead of hot glue around the inside seams as a precaution. It of course dries almost immediately. Silicone smells for a while, and I would be concerned about the solvent's impact on speaker substances, like the glues and foams and plastics used. Outgassing is also seen with rubberized stuff like Rhino liner someone mentioned, same concerns there.

Steve

[dwigle]

I have sealed some mdf interiors, usually just the larger enclosures. But I never had a problem with either. But most are veneered so I don't know if I could tell.

I did make a 2x4 table saw extension using 3/4" mdf. I used kitchen laminate for the top. Within 2 weeks I had a 3" high crown in the middle of the panel.

I threw that one out and built another and laminated both sides. No bowing after 5 years in a humid Florida garage shop.

[johnastockman]

So what you're saying is that you seal your inside depending on your mood ? By the way, what is "Rubberized undercoating" ? Do you use any specific product ?



That's an interesting point of view but I don't think I'll ever veneer the inside of a speaker!!! Way too expensive! LOL!

Yesterday I've used a mix of 50/50 glue/water to seal the inside and outside of my latest enclosure and then sanded it with 220 grit. It really does a good job so I think I'll stick with that method until I find something better or easier (if that's possible)

Thanks for your inputs guys and sorry the late reply! (Better late then never they say)

Chuck

Any of the methods mentioned will work, but is it sealing the seams/corners or the interior surface? I guess either case, the same idea would seal seams/corners, including the inside surface. I've always used something that coated the entire interior...the glue one you mentioned and also this marine epoxy I get. Something else that works is your favorite brand of DIY bedliner sauce, as opposed to the undercoating. Duratex and Duplicolor are great products. Duratex (not as toxic) is roll or brush-on, the Duplicolor (smelly and wear a respirator) has spray cans along with brush-on. For a spray can, the Duplicolor has a superior spray-head compared to the other spray-on brands. I've also used a Cascade Audio product for over 12 years, VB-1. I'm sure that the bedliner stuff and the VB-1 is a little OCD on my part, but a simpler, less-expensive method like the glue or shellac will have the same desired results. It's possible to gain a small improvement just by checking the commercial speakers one might have. I've seen seam & corner gaps (not visible until you look from the inside out) and ports, terminal plates, and drivers that didn't have a good seal around their mounting flanges in quite a few retail speakers. From HTIB's/rack systems to popular, recognized brands. Some caulk or silicone around all the interior seams and some inexpensive weatherstripping for the ports/terminals/drivers can make enough of an improvement in the bass frequencies to be noticed. Not dramatic, but just a bit more refined or accurate. My brother-in-laws Cerwin Vega's were a typical example. Floorstanding 3-way w/15" woofer, sealed-back paper-cone mid maybe 5", and a "horn" tweeter. IIRC, a front port. Nice 3/4" thick cabinet material, but no bracing and leaky seams and driver frames. Just getting them sealed up made a difference that he noticed right away. Even more so when he put some of that roll-on bedliner all over the inside, closet-rod doweling for braces (5 pieces: 3 side-to-side, 2 front-to-back), and 3 layers of 1" thick dacron batting on the inside walls. The bass response was tighter, less boomy or "one note". If you have a nice matching glueing surface, whether it's a but*-joint, rabbet/dado or mitered, and you're not stingy with the glue, you'll get a sealed joint, so unless you're the slightly obsessive kind like me, I wouldn't worry about any air leaks. A bright light in the box can show gaps if you think you might have one.

John A.

[NyxOne]

Depends on what you mean by "sealing" I'll run a bead of caulk around the inside of all the corners and smooth it with my finger. It looks nice and helps me sleep at night, whether it does anything else I have no clue. As for any other type of sealing, well most of those surfaces are covered in some kind of adhesive and sound damping so there isn't much point in doing anything else to them, I think.

Well now that I think of it I should have been a bit more clearer about what kind of sealing I was talking about.

What I meant is : Is there any advantage of sealing the MDF inside an enclosure ? We usually seal the outside by applying glue, paint, veneer, etc.

I know that some manufacturer (eg: Totem Acoustics) seal the inside of their enclosure but usually don't explain why. I have my doubts but I'm not sure. One of them is to prevent the MDF to soak humidy which prevent expansion or contraction of the material.

Any thoughts on this ?

BTW, thanks for all your reply! I was not expecting that much!

Chuck

[evilskillit]

Well in a sealed box the chances of the humidity changing inside the box once its built are pretty low I would imagine.

In a ported box, well I doubt it seriously matters, but if you want you can just slosh some latex paint or fiberglass resin around inside the box before you finish it off. Probably won't do much but like insanely expensive interconnects and whatnot, if it makes YOU feel better then its worth doing. If not save the time and put it towards another project, or spend it with your family.

[mike s]

Those using silicon on the seams might consider using polyseamseal all purpose adhesive caulk , it's water based, uses pva (as in white glue) , and washes up with water.


http://www.polyseamseal.com/allpurpose.shtml

[evilskillit]

Those using silicon on the seams might consider using polyseamseal all purpose adhesive caulk , it's water based, uses pva (as in white glue) , and washes up with water.


http://www.polyseamseal.com/allpurpose.shtml

Ditto, easy to work with, easy to clean up and you don't have to worry about it offgassing and destroying your drivers like silicon has the remote chance of doing.

[hulan]

My question would be, does sealing the inside of the speaker change the resonance/damping of the MDF (assuming that's what you're building with)?
I'm always down to try anything once, but why not save time and money and ask someone who has tried it.


Mike S. good lookin' out. I like the whole water cleanup thing without the fumes. I'm often stuck doing things in the office upstairs (small room) so fumes are a bad thing. I remember picking it up by accident and using it, liked it, but couldn't remember what the heck it was.