[lacro]

What about going over the  seams with  "bondo" or some other  body filler ?

-jay

 Actually I tried some of these methods today as an experiment on my cabinets.
I used the bondo on some low spots, and tried automotive spot putty as well. The problem is bondo is for filling shallow dips, and spot putty is for filling pin holes. If used on a smooth flat surface like the butt joint that have been made perfectly level with the router, bondo or spot putty will be sanded completely off.

 They both have a use on MDF cabinets, but IMO not for sealing the seam. I am hoping epoxy, especially thinned will help seal the joint. I think what is actually happening at the butt joint is expansion/contraction because of already absorbed moisture in the MDF.

 I wonder if baking the cabinets in the oven at something like 150F would drive out the moisture without destroying the glue, and stabilize the MDF before painting?

Larry..

[django11]

Scott,
 I may give the epoxy a try, I happen to have several gallons. I may try thinning it for max penetration, even though that's normally a bad idea as it reduces strength.
 I hope your theory is correct as I have already soldered the wires on the boards using red as plus. Maybe Danny can confirm the broader tabs are indeed + on these drivers?
 My biggest concern with painting is the butt joints showing through the paint.


Larry

I think epoxy would be ok as long as you know your finish paint will adhere to it.  I would be surprised if the butt joint ever becomes totally invisible. Over time variations in humidity levels will make the mdf expand differently on the length and thickness.   The higher the gloss on the finish and the more it will show. 

[Captainhemo]

I would be surprised if the butt joint ever becomes totally invisible. Over time variations in humidity levels will make the mdf expand differently on the length and thickness.   The higher the gloss on the finish and the more it will show.

That's why I think I'll stay with the spray on truck bed liner.  It's  more like a satin black  and it's not perfectly flat.   When I did  my sub box,  I   used  2 coats of primer first  (tinted black) .  So far,   it's  hiddent the seams  very well.

-jay

[mrhyfy]

why not cover the exposed ends of the cabinet  in thin 1/8 mdf (masonite?).
The exposed edge from the masonite is easy to sand smooth..

[jwern6]

Gotta throw my two cents in, here.  I used Duratex on some X-LS & a sub for my son and it worked great.  Got it from a place in Ft Lauderdale.  (www.acrytech.com)  It is roller grade, satin finish, and you can vary the height of the "finish" to get smooth or as rough as you want it.  I used Lowe's bedliner on a set of mdf boxes and it was very rough to the touch ( but bullet proof).  This Duratex is a great product, and durable as well. The speakers will look like they are ready for road tour.  WAF might be a little low, but the finish is super tough. check it out. 

[django11]

Duratex actually has a sound damping coating for the interior of the cabinet http://store.acrytech.com/Speaker-Cabinet-Coating-Acoust-X-Sound-Damping-Coating.html.  I know, it ain't No Rez but a couple of coats and a dipple finish must get you part way there ( maybe even a few coats over vinyl tile?)

[lacro]

Well,
 I did a lot of research on several forums trying to see how everyone else seals MDF. This product (MDF) is used for many many uses besides speakers.
Here is some of what I have found:

• MDF absorbs moisture
• Absorbing moisture/drying cycle causes seams to show
• sealing both the inside and outside is required to slow moisture absorption in speaker cabinets
• Wood glue allows movement at the seams
• Epoxy glue will help prevent the seam movement
• As I had thought, pre warming the MDF prior to any sealing will reduce absorbed moisture
• Epoxy seals MDF very well, plus it hardens it

 I found several posts on speaker building sites as well as Pro-construction builder forums about these same issues we encounter using MDF for speakers and stands. The overwhelming consensus is Epoxy glue is better than wood glue for panel assembly. Also, all surfaces inside and out should be sealed, epoxy is the best sealer. This is after all possible moisture is driven out of the MDF.

 I know everyone has there own method of building, and have developed what you feel is the tried and true "best" method. However, the internet is a great resource for information, but we all know "it's worth exactly what we pay for it" I have a lot of experience with Epoxy, and related fillers, so I will be the tester for the use of epoxy, and will report my finding.

Larry

 

[Captainhemo]

Good stuff Larry,  looking forward to hearing   how things go.
Too bad  you didn't come across this info earlier,   you could have done the insdide before gluing in the  vinyl and insulation.
With no  compressor  or spray gun,  coating with expoxy   will be out of the question for me..  I'm wondering  how strong the truck bed liner is,  wonder if it helps  eliminate  movement in the seams.  No seams are showing  through so far on my sub.
Anyway, keep us posted

[lacro]

Good stuff Larry,  looking forward to hearing   how things go.
Too bad  you didn't come across this info earlier,   you could have done the insdide before gluing in the  vinyl and insulation.
With no  compressor  or spray gun,  coating with expoxy   will be out of the question for me..  I'm wondering  how strong the truck bed liner is,  wonder if it helps  eliminate  movement in the seams.  No seams are showing  through so far on my sub.
Anyway, keep us posted

 There's a lot of things I could have done differently, and at the end of my build I will document them all so those that follow may have an easier time (pay it forward). Also, my next build will go smoother. I do think the application of contact cement is a good sealer along with the floor tiles. I had also caulked all the seams after installing the tiles.

Larry

[Peter J]

• MDF absorbs moisture
• Absorbing moisture/drying cycle causes seams to show
• sealing both the inside and outside is required to slow moisture absorption in speaker cabinets
• Wood glue allows movement at the seams
• Epoxy glue will help prevent the seam movement
• As I had thought, pre warming the MDF prior to any sealing will reduce absorbed moisture
• Epoxy seals MDF very well, plus it hardens it

Lacro, I'd agree with most all that but it needs some clarification. All wood and wood products absorb and dissipate moisture, MDF has no particular penchant for attracting (or releasing) moisture. We're not talking about moisture in liquid form but rather vapor, which most would refer to as humidty...and there's always some humidty in the environments we live in...it's everwhere in varying levels. Wood movement will be affected by both humidity and temperature.

Stopping the give and take of moisture is to fly in the face good ol' Mother Nature and she always wins in the end. The best we can reasonably hope for is to slow the give and take down some.

As to glues, most wood glues form what is called a flexible glue line, giving it the alility to move with the wood it's sticking together. Most epoxies have a much more ridgid glue line. Neither is necessarily better, but rather which one works for the intended application. In the case of speaker boxes, either will work in my experience, so it depends on what you're doing and the desired results.

I'm not sure the sealing of cabinet interiors has any real-world effect on plywood or MDF speaker cabinets, but generally its effects are well known in the woodwoking world...often referred to as "balancing" a panel for the reasons you describe.

Ideally you want any wooden structure to be constructed in the humidty and temperature environment it will ultimately live in. If you purposely dry it further it will simply equalize itself to the existing conditions after the heat is removed, and movement will occur in greater amounts. It may take some time, but once again Mother Nature will prevail in the long haul.

[SteveRB]

If you purposely dry it further it will simply equalize itself to the existing conditions after the heat is removed, and movement will occur in greater amounts. It may take some time, but once again Mother Nature will prevail in the long haul.

This is a very good point. I would also hesitate to seal the inside - the inside surface of the wood/mdf will allow the material to acclimatize gradually to changing humidity and temperatures (throughout the seasons, year after year).

[cody69]

Another option to consider for a textured painted surface is a hammered finish paint. It falls in the middle between a standard smooth surface, and the more highly textured bed liner finish. Hammerite has been around for years, and now companies like Rustoleum make a similar product that is available in big box  srores. You can build up a finish as thick as you need to help hide the seams.

I use this for painted surfaces exposed to lots of use since it is very durable and wears like iron. I also used it on a pair of x-ls cabinets earlier this year that needed extra protection. The picture below isn't great, but will give you an idea what it looks like and if this might work for you.

[Danny Richie]

Cody, that looks real good.

[lacro]

Cody, that does look good. I have used it on speaker stands, but it ran on vertical surfaces, so I painted it black which looked pretty good, but no hammered look.
Larry

[django11]

Lacro, I'd agree with most all that but it needs some clarification. All wood and wood products absorb and dissipate moisture, MDF has no particular penchant for attracting (or releasing) moisture. We're not talking about moisture in liquid form but rather vapor, which most would refer to as humidty...and there's always some humidty in the environments we live in...it's everwhere in varying levels. Wood movement will be affected by both humidity and temperature.

Stopping the give and take of moisture is to fly in the face good ol' Mother Nature and she always wins in the end. The best we can reasonably hope for is to slow the give and take down some.

As to glues, most wood glues form what is called a flexible glue line, giving it the alility to move with the wood it's sticking together. Most epoxies have a much more ridgid glue line. Neither is necessarily better, but rather which one works for the intended application. In the case of speaker boxes, either will work in my experience, so it depends on what you're doing and the desired results.

I'm not sure the sealing of cabinet interiors has any real-world effect on plywood or MDF speaker cabinets, but generally its effects are well known in the woodwoking world...often referred to as "balancing" a panel for the reasons you describe.

Ideally you want any wooden structure to be constructed in the humidty and temperature environment it will ultimately live in. If you purposely dry it further it will simply equalize itself to the existing conditions after the heat is removed, and movement will occur in greater amounts. It may take some time, but once again Mother Nature will prevail in the long haul.

A better approach to this would be to design the speaker with fewer butt joints.  A more challenging build:  45s on top and fronts.  Back and bottoms get butt joints...

[lacro]

Lacro, I'd agree with most all that but it needs some clarification. All wood and wood products absorb and dissipate moisture, MDF has no particular penchant for attracting (or releasing) moisture. We're not talking about moisture in liquid form but rather vapor, which most would refer to as humidty...and there's always some humidty in the environments we live in...it's everwhere in varying levels. Wood movement will be affected by both humidity and temperature.

Peter, From my experience, MDF does have a penchant for attracting moisture. The MDF I am using for my speakers was stored in a dry garage off the floor together with some plywood and OSB. The MDF from the bottom of the sheets up about 1 foot were swollen to almost 7/8" IMO/ MDF absorbs moisture, swells and does not go back to its original thickness when it dissipates the moisture. The other sheet goods did not exhibit this swelling. MDF is pulverized wood with binders that is compressed to sheet form. It does not have the cellular structure of wood which absorbs and dissipates moisture freely, allowing the wood to revert back to its original dimension. MDF keeps its swollen state. IMO this is why butt seams show through paint, and don't shrink back like wood. This probably has a lot to do with where I live. I see high heat/humidity in the summer, and bone dry humidity in winter with lots of temperature extremes[/quote]

Stopping the give and take of moisture is to fly in the face good ol' Mother Nature and she always wins in the end. The best we can reasonably hope for is to slow the give and take down some.

 I agree, but that's exactly what boat builders are trying to achieve, total encapsulation of the wood so there is no moisture give and take at all. It's worked very well for me.
 

As to glues, most wood glues form what is called a flexible glue line, giving it the alility to move with the wood it's sticking together. Most epoxies have a much more ridgid glue line. Neither is necessarily better, but rather which one works for the intended application. In the case of speaker boxes, either will work in my experience, so it depends on what you're doing and the desired results.

Again, I agree with the flexible glue line which for furniture is an attribute. Most furniture is finished in lacquer, which breaths somewhat, and the inside is left unfinished. The give and take of moisture
you mention is allowed, and a flexible glue joint is important. As you point out, epoxy used as a glue is a rigid glue line, and is probably not a good choice for wood furniture. However, in my experience, MDF absorbs moisture and swells the joint. A rigid glue line should help keep a butt joint tight as would mechanical fasteners (i.e. screws, staples) or biscuits.
 

I'm not sure the sealing of cabinet interiors has any real-world effect on plywood or MDF speaker cabinets, but generally its effects are well known in the woodwoking world...often referred to as "balancing" a panel for the reasons you describe.

I am not sure either, but from my boat build experience, total epoxy encapsulation does completely seal out all give and take of moisture on wood, creating a truly water proof structure, thus fooling mother nature. However, nothing is forever, and mother nature will always prevail in the end. We can just hope we outlive the inevitable. Also, I have no idea if epoxy will work as well in MDF which absorbs any liquid like a sponge. From the info I have garnered on speaker building forums, it will help a lot.

 

Ideally you want any wooden structure to be constructed in the humidty and temperature environment it will ultimately live in. If you purposely dry it further it will simply equalize itself to the existing conditions after the heat is removed, and movement will occur in greater amounts. It may take some time, but once again Mother Nature will prevail in the long haul.

If we were talking about wood, I would agree, but in my environment, MDF is not very stable, and sucks humidity like it's a sponge . I think driving out all possible moisture before total encapsulation is prudent. This suggestion was found on speaker building forums so I really don't know whether it will be a benefit or not, but it makes sense if one is completely sealing all surfaces.

Peter... This is just a discussion about how to prevent butt seams showing on painted speaker cabinets. I value your opinion, and I know you are a superb wood worker. I welcome all opinions and ideas in my build thread. I am hear to learn, and appreciate all suggestions. I don't know what  will work best for my situation, but I don't have a lot invested so I will try my theory and let everyone know the results.

Thanks for your input, rebuttals are welcome.

Larry 

[lacro]

A better approach to this would be to design the speaker with fewer butt joints.  A more challenging build:  45s on top and fronts.  Back and bottoms get butt joints...

I agree it would probably solve the joint show through,I also agree with the "more challenging build"  45 miters on a box are for better wood workers than me!

Larry

[Captainhemo]

I wonder if  nusing small "L' brackets on the inside  of the cabinet before   the lining went in  would help to reduce the joint show through" ?  Sounds like we need to be painting  with Linux,  you know that  stuff they use to bomb proof walls etc  !!

I wonder if we shouldn't be looking at different materials for  construction.  The additional cost may be offset  by the  time/money spent trying to totally seal a cabinets panels ?

-jay

[lacro]

Some progress:

Tinning the cross-over leads with solder


The first ones soldered to a cross-over


 Cross-over with all leads soldered (top)


Bottom



Long board sanding to level all sides


Low spots marked for filling






Baffles glued on with thickened epoxy


Larry

[jwern6]

those boxes are lookin good.  may I say, about crossover boards; get the sonicaps and mills resistors. now is the time. they will take your speakers up a couple of notches. or at least make your x-over boards very accessible because you will get the urge later. just sayin. I for one am anxious to see the final poduct here.