[jcsperson]

The worst is the fine dust that it creates, which is partially wood fibers and partially glue.  I don't like breathing it or having to clean it up all over the shop.  It spreads much worse than sawdust.

Then there is problem of rapidly wearing down cutting tools like table saw blades and router bits.

MDF is also very poor at holding screw treads.  Many people who use it resort to inserts for attaching drivers just to be sure of a tight attachment.  Not usually a problem with real wood.

And then there is the issue of finishing.  It's fine if you want to paint it, but otherwise it requires veneering, which is a lot of work.

 

All valid. I hate the stuff.

BB can be found in a variety of wood types and finished like any other wood project.  There is an issue, however, with the edges that show all the layers.  That can be addressed by miter corners if you are willing to give up rounded over baffle edges.  Or better yet use a solid wood baffle and use BB plywood for the rest of the box.  Then there will be no edges visible.

Another possibility is to simply glue a strip of hardwood to the edge of the plywood. A 3/4 x 3/4 piece of hardwood could be glued to the ply edge then another piece of ply attached to that at 90° to form a corner. An advantage of that is you could use a roundover bit to smooth out the look of the edge without exposing any plies.

https://img.canuckaudiomart.com/uploads/large/427079-1668c014-one_canton_karat_300_speaker.jpg

A cool way to join two plywood edges at 90° is a bird mouth joint. It looks a bit complicated, but it's really just 45° cuts on a table saw.

http://images.meredith.com/wood/images/2006/01/p_birdsmouth3.jpg

[FullRangeMan]

MDF is also carcinogenic due emission of formaldehyde vapors for 5 years so it is resistant to insects.

[Peter J]

MDF is also carcinogenic due emission of formaldehyde vapors for 5 years so it is resistant to insects.

Despite continually banging that drum, FRM, it's just not true of MDF manufactured in North America and hasn't been for a good long time. The insect resistance you infer is simply nonsense for anything used in the furniture and cabinetry industry and sourced in USA or Canada. Perhaps an insecticide is used in siding products, but it wouldn't be urea formaldehyde. I don't know about the rest of the world.

[FullRangeMan]

it's just not true of MDF manufactured in North America
Do you could prove it?
What they use ?

[Peter J]

it's just not true of MDF manufactured in North America
Do you could prove it?
What they use ?

Yes, I can. The only non-NAUF products being sold now come from outside USA and Canada.
 
https://www.rugbyabp.com/resources/green-products/nauf-product-information

http://www.integratedwoodcomponents.com/NAUF-Plywood-Manufacturers/tabid/1989/Default.aspx

https://www.snwwood.com/Lumber-Plywood/FSC-Plywood

http://www.socomi.com/build_green.shtml

https://www.westfraser.com/products/mdf/environmental-specifications

Shall I gather more?

[FullRangeMan]

Gracias I will read tommorrow.

[diyman]

Yes, I can. The only non-NAUF products being sold now come from outside USA and Canada.
 
https://www.rugbyabp.com/resources/green-products/nauf-product-information

http://www.integratedwoodcomponents.com/NAUF-Plywood-Manufacturers/tabid/1989/Default.aspx

https://www.snwwood.com/Lumber-Plywood/FSC-Plywood

http://www.socomi.com/build_green.shtml

https://www.westfraser.com/products/mdf/environmental-specifications

Shall I gather more?

NAUF stands for No Added Urea Formaldehyde, but there is still some amount of formaldehyde in MDF.  Although with fairly recent legislation it is now required to be much lower than it was in the past.

It is also possible that there are other kinds of formaldehyde in MDF, such as phenol or melamine formaldehyde, that are not covered by the NAUF standard.  It only apples to the Urea type.

The standard is mainly intended for consumer protection against things such as pre-manufactured furniture and cabinets.  What is not clear is how much formaldehyde is released when cutting or routing the MDF material.  I'm not saying that this is necessarily a problem, I just don't know if it has been addressed by the standards or not.

[Peter J]

NAUF stands for No Added Urea Formaldehyde, but there is still some amount of formaldehyde in MDF.  Although with fairly recent legislation it is now required to be much lower than it was in the past.

It is also possible that there are other kinds of formaldehyde in MDF, such as phenol or melamine formaldehyde, that are not covered by the NAUF standard.  It only apples to the Urea type.

The standard is mainly intended for consumer protection against things such as pre-manufactured furniture and cabinets.  What is not clear is how much formaldehyde is released when cutting or routing the MDF material.  I'm not saying that this is necessarily a problem, I just don't know if it has been addressed by the standards or not.

I should point out that the NAUF standard also applies to other manufactured panels including plywood and, I think, OSB. MDF likely has greater glue content than plywood, so there's that aspect. For those wondering what UF actually is, this lifted from Wikipedia:

Urea-formaldehyde (UF), also known as urea-methanal, so named for its common synthesis pathway and overall structure,[1] is a non-transparent thermosetting resin or polymer. It is produced from urea and formaldehyde. These resins are used in adhesives, finishes, particle board, medium-density fibreboard (MDF), and molded objects.

UF and related amino resins are a class of thermosetting resins of which urea-formaldehyde resins make up 80% produced globally. Examples of amino resins use include in automobile tires to improve the bonding of rubber to tire cord, in paper for improving tear strength, in molding electrical devices, jar caps, etc.

FWIW, I was working in the RV business before NAUF was common and we would sometimes get new units in that were simply stifling to walk into after being closed up during shipping, and I think I'm pretty tolerant of such. I do see this as movement in a good direction, but if it's a concern to you, know that MDF is not the only source.

[mlundy57]

The dust from many exotic hardwoods can also be toxic. That's why good dust collection and the use of N95 masks is important no matter what type of material you are working with. Every type of material has strengths and weaknesses for any given application and every woodworker has personal preferences. Whatever you choose to work with, be safe doing it.

Mike

[diyman]

...FWIW, I was working in the RV business before NAUF was common and we would sometimes get new units in that were simply stifling to walk into after being closed up during shipping, and I think I'm pretty tolerant of such. I do see this as movement in a good direction, but if it's a concern to you, know that MDF is not the only source.

It's not really a concern.  This discussion was about MDF vs plywood for speaker cabinets and I think that the problems with MDF make it much less desirable to use.  There are only two reasons to ever use MDF.

One is that it is less expensive than plywood.  And that is obviously important to a speaker manufacturer who is trying to maximize profits.  But for a DIYer the cost difference is trivial compared to the total cost of drivers, crossover components, etc.

The other reason is if you think it sounds better than plywood.   And like most other subjective items discussed here opinions vary.   

Perhaps the best box is really no box at all.

[Hobbsmeerkat]

This has got me curious. I've seen some custom speaker builds onlinr made with inner walls of MDF, and outer walls of solid wood or plywood, (or even metal) while using some sort of rubber/tar adhesive between them to help reduce cabinet resonance. (Before any norez is added)

Does having layers of different densities & resonant frequencies  also help with reducing resonance, or is it more about mass and thickness?

[mlundy57]

It's not really a concern.  This discussion was about MDF vs plywood for speaker cabinets and I think that the problems with MDF make it much less desirable to use.  There are only two reasons to ever use MDF.

One is that it is less expensive than plywood.  And that is obviously important to a speaker manufacturer who is trying to maximize profits.  But for a DIYer the cost difference is trivial compared to the total cost of drivers, crossover components, etc.

The other reason is if you think it sounds better than plywood.   And like most other subjective items discussed here opinions vary.   

Perhaps the best box is really no box at all.

I find MDF to be easier than BB ply to cut profiles. BB has a tendency to blow out. Also, around here, BB is three times as expensive as MDF. True, if you are only building one pair for yourself the actual difference between a 4x8 sheet of MDF and a 5x5 sheet of BB ply is only $40. Another difference is you can get the MDF broken down into smaller pieces at the store while you can only get the BB ply as a full sheet. So a person's ability to get a full sheet home and broke down could also factor into the decision.

[mlundy57]

This has got me curious. I've seen some custom speaker builds onlinr made with inner walls of MDF, and outer walls of solid wood or plywood, (or even metal) while using some sort of rubber/tar adhesive between them to help reduce cabinet resonance. (Before any norez is added)

Does having layers of different densities & resonant frequencies  also help with reducing resonance, or is it more about mass and thickness?

This technique is called constrained layer damping and has it's adherents. I haven't studied the concept well enough to know if there are real advantages or not.

[HAL]

For constrained layer damping the material between layers has to be a visoelastomer, not something like rubber.  Tar is an example.

It has both liquid and solid properties.

[Peter J]

For constrained layer damping the material between layers has to be a visoelastomer, not something like rubber.  Tar is an example.

It has both liquid and solid properties.

I didn't know that...thanks Rich.  I assumed it just had to be flexible, didn't know there were specific properties involved. I wouldn't have distinguished between the two examples. Forever curious it seems, I had to do some Googling. For those interested, here's a link to what Wikipedia has to say:
 
https://en.wikipedia.org/wiki/Elastomer

About viscoelasticity specifically:

https://en.wikipedia.org/wiki/Viscoelasticity

I suppose the whole concept of constrained layer damping is interesting to me.

[Hobbsmeerkat]

For constrained layer damping the material between layers has to be a visoelastomer, not something like rubber.  Tar is an example.

It has both liquid and solid properties.

Yeah! That's it! It's been a while since I watched those videos. (Maybe a year ago beI just remembered it was some kind of elastic material that looked kinda like tar when applied.

Definitely something ill have to dig into some more!

[jcsperson]

Here's an interesting article from Troels Gravesen:

http://www.troelsgravesen.dk/cabinet-damping.htm

[planet10]

Some people believe that quality Baltic Birch plywood is better than MDF.  Has a more pleasant sound.  I use it for that reason plus I just don't allow MDF into my workshop.  Too many bad issues with it.

+1

Except for being cheap, MDF is not that good a speaker building material.

Speakers can, and have been built from solid, but you do need to know what you are doing to keep them from cracking.

I have some here in Yew and in Douglas Fir (a pine, these built from a 70-year old floor) and we have played with Western Red Cedar (a good build material except for the soft surface that easily dings) and others.

All. built by a skilled woodworker who knows what he is doing.

Fir:



Walnut:



I have many more examples if you’d like.

If you can afford it, stranded/folized bamboo plywood is an outstanding material that bringsmany of the assets of solid with the benefits of plywood.

dave

[planet10]

Another possibility is to simply glue a strip of hardwood to the edge of the plywood. A 3/4 x 3/4 piece of hardwood could be glued to the ply edge then another piece of ply attached to that at 90° to form a corner. An advantage of that is you could use a roundover bit to smooth out the look of the edge without exposing any plies.

Another example:



dave

[planet10]

Does having layers of different densities & resonant frequencies  also help with reducing resonance, or is it more about mass and thickness?

Contained layer damping works, but IMO the extra efforts bring no real benefits vrs a well engineered box.

dave