Sealed Enclosures with MDF

  • Thread starter Fishbowl Dominc
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Fishbowl Dominc

Audiophyte
Does MDF really provide a sealed enclosure if left untreated or unpainted? The reason why I ask... I heard MDF is incredibly porous. For example, I've heard that by putting an end of a vaccuum hose on one side of a .75" MDF board and a piece of paper on the other side, the paper will stick to the board because of the vacuum. I would think this would interfere with some of the acoustical physics... causing the speaker to perform less than ideal. If this is the case, I wonder if just painting the inside (and perhaps outside too if you want to for cosmetic reasons) with a oil based primer would solve this issue.
 
everettT

everettT

Audioholic Ninja
Does MDF really provide a sealed enclosure if left untreated or unpainted? The reason why I ask... I heard MDF is incredibly porous. For example, I've heard that by putting an end of a vaccuum hose on one side of a .75" MDF board and a piece of paper on the other side, the paper will stick to the board because of the vacuum. I would think this would interfere with some of the acoustical physics... causing the speaker to perform less than ideal. If this is the case, I wonder if just painting the inside (and perhaps outside too if you want to for cosmetic reasons) with a oil based primer would solve this issue.
MDF unfinished isn't leaky unless you didn't caulk or seal the seams on the inside or have bad joints. I've had unfinished MDF speakers that were in service for years.
 
highfigh

highfigh

Audioholic Slumlord
Does MDF really provide a sealed enclosure if left untreated or unpainted? The reason why I ask... I heard MDF is incredibly porous. For example, I've heard that by putting an end of a vaccuum hose on one side of a .75" MDF board and a piece of paper on the other side, the paper will stick to the board because of the vacuum. I would think this would interfere with some of the acoustical physics... causing the speaker to perform less than ideal. If this is the case, I wonder if just painting the inside (and perhaps outside too if you want to for cosmetic reasons) with a oil based primer would solve this issue.
"Incredibly porous"? Where did you hear that?

You couldn't lose pressure through MDF with a woofer if your life depended on it- whatever you heard about paper being sucked against the MDF just because of a vacuum, is plain wrong. Or, the MDF they used was crap and there are different grades of just about all lumber products. However, MDF is actually more of a paper than lumber- it's a slurry that's rolled and pressed- if you snap a 1" wide piece of it, it will actually delaminate, unlike particle board or wood.

I couldn't begin to guess the number of enclosures that I have made of MDF and never had a problem, but I also never heard of that story about pulling vacuum through it, either.

If you're concerned, coat it with paint or, if you'll use it in a wet environment, coat it with polyester resin or epoxy.

There's a saying- "if your sealed box has a small leak, you might as well make it a large one". This is such a small leak that it's inconsequential.

Why would you need oil based primer- all paints will seal it but again, it's not necessary.

If you want, I'll test this theory today- I have shop vacs and a dust collector that pulls even harder.
 
F

Fishbowl Dominc

Audiophyte
"Incredibly porous"? Where did you hear that?

You couldn't lose pressure through MDF with a woofer if your life depended on it- whatever you heard about paper being sucked against the MDF just because of a vacuum, is plain wrong. Or, the MDF they used was crap and there are different grades of just about all lumber products. However, MDF is actually more of a paper than lumber- it's a slurry that's rolled and pressed- if you snap a 1" wide piece of it, it will actually delaminate, unlike particle board or wood.

I couldn't begin to guess the number of enclosures that I have made of MDF and never had a problem, but I also never heard of that story about pulling vacuum through it, either.

If you're concerned, coat it with paint or, if you'll use it in a wet environment, coat it with polyester resin or epoxy.

There's a saying- "if your sealed box has a small leak, you might as well make it a large one". This is such a small leak that it's inconsequential.

Why would you need oil based primer- all paints will seal it but again, it's not necessary.

If you want, I'll test this theory today- I have shop vacs and a dust collector that pulls even harder.
I'm not disagreeing with your notion that MDF enclosures are perfectly fine... Maybe not being completely air tight is actually a good thing, and helps reduce resonance by dissipating some of the sound energy and reduces chances of standing waves. Also, MDF board is kind of a broad term... just because one brand of MDF is air tight doesn't mean another type of MDF is air tight...
 
TLS Guy

TLS Guy

Seriously, I have no life.
I'm not disagreeing with your notion that MDF enclosures are perfectly fine... Maybe not being completely air tight is actually a good thing, and helps reduce resonance by dissipating some of the sound energy and reduces chances of standing waves. Also, MDF board is kind of a broad term... just because one brand of MDF is air tight doesn't mean another type of MDF is air tight...
I have NEVER encountered MDF that was not airtight. It is all put together with glue. If it did leak, it would not be a good enclosure. I suppose there could be some junk foreign MDF around some place. Here in Minnesota up in our Northwoods, we make tons of the stuff, and I can assure, none of it is leaky!
 
highfigh

highfigh

Audioholic Slumlord
I'm not disagreeing with your notion that MDF enclosures are perfectly fine... Maybe not being completely air tight is actually a good thing, and helps reduce resonance by dissipating some of the sound energy and reduces chances of standing waves. Also, MDF board is kind of a broad term... just because one brand of MDF is air tight doesn't mean another type of MDF is air tight...
No, if you want a sealed enclosure,it needs to be sealed. All an enclosure does is make the air vibrate sympathetically with the driver and the box volume will determine how correctly it does this, based on the driver's characteristics- the driver always determines the box, never the other way around.

I used MDF from Home Depot and Menards and it was crap, but not because I think it leaked but because it lacked the stiffness I had been accustomed to when using the MDF sold by a distributor that served the cabinetmaking industry. I would avoid big box building materials and look for something better. The cheap stuff tends to be darker and it looks almost like Masonite- that's not a good thing. If you can, use MDF from Weyerhauser/Plumb Creek or something similar.

MDF means 'Medium Density Fiberboard', but if you do a search for 'MDF', you'll see photos that show a wide range of colors and particle size. All building materials will show various specs, like density, stiffness, etc- use those if you want a good result.
 
F

Fishbowl Dominc

Audiophyte
No, if you want a sealed enclosure,it needs to be sealed. All an enclosure does is make the air vibrate sympathetically with the driver and the box volume will determine how correctly it does this, based on the driver's characteristics- the driver always determines the box, never the other way around.

I used MDF from Home Depot and Menards and it was crap, but not because I think it leaked but because it lacked the stiffness I had been accustomed to when using the MDF sold by a distributor that served the cabinetmaking industry. I would avoid big box building materials and look for something better. The cheap stuff tends to be darker and it looks almost like Masonite- that's not a good thing. If you can, use MDF from Weyerhauser/Plumb Creek or something similar.

MDF means 'Medium Density Fiberboard', but if you do a search for 'MDF', you'll see photos that show a wide range of colors and particle size. All building materials will show various specs, like density, stiffness, etc- use those if you want a good result.
Okay, I usually get my MDF from Lowes... seems pretty sturdy to me.

 
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highfigh

highfigh

Audioholic Slumlord
F

Fishbowl Dominc

Audiophyte
Do you have them make a couple of cuts for you, or do you hoist the whole sheets by yourself? Fun, eh? 105lb/sheet- awkward, yet bulky.

If it looks like the MDF in the photo, you should be OK. BTW- it withstands water contact pretty well, too- far better than particle board.

View attachment 57682
The last time I was there they cut it for me into 4 sections per my request... that was years ago. I don't know if they would do that for me anymore. Then I did the rest of the cutting at home with my table saw. I guess they think everybody in Pennsylvania has a 4wheel drive pickup truck because of the horrible road conditions in winter.
 
WookieGR

WookieGR

Full Audioholic
MDF is an excellent material to use for speaker building. Proper amounts of fasteners and wood glue will give an air tight seal.

However, MDF is highly toxic and contains glues and chemicals that are cancerous. Sealing the box with at least wood sealer is preferred over leaving it raw to potentially contaminate the air over time. Getting it wet will also cause it swell up and sealing it prevents that too.

Never just leave an MDF box untreated if it's used in a populated area and there are pets or kids around.
 
Swerd

Swerd

Audioholic Warlord
… MDF is highly toxic and contains glues and chemicals that are cancerous. Sealing the box with at least wood sealer is preferred over leaving it raw to potentially contaminate the air over time. Getting it wet will also cause it swell up and sealing it prevents that too.
Although the warning about MDF has often been repeated on the internet, it isn't true. MDF is not toxic. And breathing 'MDF fumes' cannot cause cancer.

Formaldehyde can be toxic if you're directly exposed to it at high concentrations. The wood fibers in MDF are bound together, using formaldehyde with high heat and pressure. Once cured, the formaldehyde is chemically bound to the wood fibers and is no longer free to escape.

As you pointed out, there are good reasons why we should seal MDF from moisture. But sealing it from moisture has nothing to do with making MDF safe in our homes.
 
WookieGR

WookieGR

Full Audioholic
Although the warning about MDF has often been repeated on the internet, it isn't true. MDF is not toxic. And breathing 'MDF fumes' cannot cause cancer.

Formaldehyde can be toxic if you're directly exposed to it at high concentrations. The wood fibers in MDF are bound together, using formaldehyde with high heat and pressure. Once cured, the formaldehyde is chemically bound to the wood fibers and is no longer free to escape.

As you pointed out, there are good reasons why we should seal MDF from moisture. But sealing it from moisture has nothing to do with making MDF safe in our homes.
Wood dust and formaldehyde are group 1 carcinogens. I'm sorry you feel compelled to expose my lies for the better of all mankind.
 
lovinthehd

lovinthehd

Audioholic Jedi
Personally don't even want to deal with mdf dust, prefer baltic birch for cabinets....the dust isn't as bad but I'd still wear a mask. Plus its easier to move around and a bit sturdier in general....

ps never heard the vacuum/paper thing before, that would have to be some seriously crappy mdf....
 
Swerd

Swerd

Audioholic Warlord
Wood dust and formaldehyde are group 1 carcinogens. I'm sorry you feel compelled to expose my lies for the better of all mankind.
"Exposing lies" are your words. I never claimed you lied. What you said previously about MDF is misleading.

MDF and plywood, as they are used in home construction and furniture manufacture, are safe. The same goes for loudspeaker cabinets. If they were "highly toxic" they would have been banned when US laws were written regulating it's manufacture and use.
https://en.wikipedia.org/wiki/Sawdust#Health_hazards

Formaldehyde, when in concentrated and unreacted forms, is dangerous stuff. It is more carefully regulated in those industries where workers can be regularly exposed to high levels, such as manufacturing plywood or MDF.
 
Swerd

Swerd

Audioholic Warlord
Personally don't even want to deal with mdf dust, prefer baltic birch for cabinets....the dust isn't as bad but I'd still wear a mask. Plus its easier to move around and a bit sturdier in general...
Baltic birch as well as other plywoods are all glued up with the same formaldehyde methods as for MDF, heat and very high pressure.

Yes, when you cut or rout MDF, it makes a lot more fine sawdust than solid or plywoods. It is irritating to breathe it as you work with it.

But the people who suffer from exposure to MDF dust or formaldehyde work in industries where they are exposed every day, all day. I've never heard of a loudspeaker owner or a DIY speaker builder who had those problems.
 
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j_garcia

j_garcia

Audioholic Jedi
I never had a problem with a sealed MDF box. IIRC, I would say the vast majority of common speaker brands are made with MDF.
 
highfigh

highfigh

Audioholic Slumlord
The last time I was there they cut it for me into 4 sections per my request... that was years ago. I don't know if they would do that for me anymore. Then I did the rest of the cutting at home with my table saw. I guess they think everybody in Pennsylvania has a 4wheel drive pickup truck because of the horrible road conditions in winter.
They should be able to do that, even if it's not totally accurate for your project- it sure beats having to lift the whole sheet. If you see something similar to what's in the photo AND have someone who knows how to use it, you shouldn't have a problem-

A 2 wheel drive pickup should be fine unless you have to go up steep hills. If anything, the traction and control should be better with a load in the back, unless it's centered too close to the tailgate. I had a pickup and driving it during Winter was no problem. The problem was other drivers.

1662555225048.png
 
highfigh

highfigh

Audioholic Slumlord
MDF is an excellent material to use for speaker building. Proper amounts of fasteners and wood glue will give an air tight seal.

However, MDF is highly toxic and contains glues and chemicals that are cancerous. Sealing the box with at least wood sealer is preferred over leaving it raw to potentially contaminate the air over time. Getting it wet will also cause it swell up and sealing it prevents that too.

Never just leave an MDF box untreated if it's used in a populated area and there are pets or kids around.
It's not that bad- the photo I posted shows a thin layer at the surface- that's where the glue and fibers form a skin, which is pretty durable. It won't shed dust unless the edges are exposed and they're disturbed.

I used MDF to build a short wall in a car stereo installation shop, to prevent customers wandering into the bays and bothering the installers. A sprinkler head went off and the bottom of the wall was exposed to standing water over the weekend because the maintenance crew didn't bother to mop the floor, but the wall was fine- the bottom edge was the only part that was exposed.

MDF isn't the same as it was in the past, either Well, unless it's imported. Also, some companies make it with safer resins, so it doesn't off-gas toxins.

 
highfigh

highfigh

Audioholic Slumlord
Although the warning about MDF has often been repeated on the internet, it isn't true. MDF is not toxic. And breathing 'MDF fumes' cannot cause cancer.

Formaldehyde can be toxic if you're directly exposed to it at high concentrations. The wood fibers in MDF are bound together, using formaldehyde with high heat and pressure. Once cured, the formaldehyde is chemically bound to the wood fibers and is no longer free to escape.

As you pointed out, there are good reasons why we should seal MDF from moisture. But sealing it from moisture has nothing to do with making MDF safe in our homes.
I would add that inhaling any wood dust should be avoided, especially the species that are known to cause allergic reactions, like Walnut. MDF dust can be extremely fine, so a good dust collector and/or mask should be used.

Here's a link that probably has more info than anyone really wants, but.....

 
A

Audiophile Heretic

Audioholic Intern
Does MDF really provide a sealed enclosure if left untreated or unpainted? The reason why I ask... I heard MDF is incredibly porous. For example, I've heard that by putting an end of a vaccuum hose on one side of a .75" MDF board and a piece of paper on the other side, the paper will stick to the board because of the vacuum. I would think this would interfere with some of the acoustical physics... causing the speaker to perform less than ideal. If this is the case, I wonder if just painting the inside (and perhaps outside too if you want to for cosmetic reasons) with a oil based primer would solve this issue.
I don't think MDF is porous. I would think the resin between the wood fibers will sufficiently seal MDF from air flow if not painted. I think the quality of your joints is more important. Even non-porous panels can flex and pass sound.
 

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