Why not MDF?

[gnugear]

I've been searching the forums but can't find much info on the matter of MDF, besides "don't use it".

What's the reasoning since most conventional speaker cabs are made of it? Do horns need the added resonance of ply?

[blumenco]

I feel that horns need the extra stiffness of the ply.

the grain of real wood tends to be stiffer than particle board. add the crossgraining of a ply action, you have a substance of lower internal loss/higher relfection than MDF. the MDF "sings" MORE of its own sound than the ply, the ply lets you hear more of the initial energy of the driver.

the specific gravities of the woods are similar. that is BB to MDF. of around .6 while mdf has the "ideal" specific gravity for BLH construction, it just does not do the trick.

i am not a formal scientist about this stuff, but have tried both substances myself in identical horn enclosures. I use strictly birch ply with dense solids as driver mounts, but other woods work well.

lots of people tend to refer to MDF as emduuuf. it just kinda sounds like that too. BLH or bus reflex builds. duuuff dufffff duf duf duf duuuuuf duuuuf. I am hearing the basslines echo in my head from many a monkey coffin speaker. the bass is plump, and truely fat. and not with a PH. just an ufffey resonatey sound hanging over your entire consciousness while listening to the speaker. like the first few milliseconds of a cow getting hit by a car travelling 60 MPH. but less organic sounding.

note that not all studio monitors are made of MDF either. the world is filled with choices. I have seen people on this forum for years... I made my blh enclosures out of MDF... what is wrong with the drivers? I have all this damping in the horns... etc. etc. months later, they give up the progect or simply rebuild the enclosures out of suitable wood after being made aware of their mistakes by people on this forum.

I am not one to shut down the notion of science. we must always be experimenting, and there ARE applications of horns where MDF is called upon. it is just usually a good idea to start with plywood and go from there.

lighter specific gravity plywoods, like the poplar cores found in the us give a nice tonal sound. lots of flourishing. a nice effect. think of birch as more of a studio sound in the plywood arena.

Clark

blumenstein-ultra-fi.com

[planet10]

Most commercial cabinets use it because it is cheap (to buy, to use, to finish), Manufacturers have propagated the MDF myth so far & wide, most of them believe it themselves.

Properly done, a plywood cabinet will be less "resonate" than MDF, and doesn't suffer the energy storage of MDF.

dave

[gnugear]

Thank you very much. I'll stick to birch ply.

Do you think thickness matters much? I'm going to use 1/2" for the internal walls and 3/4" for the top and bottom. Just not sure if I need 3/4" for the side walls.

BTW, I'm following the Z-horn Heruka plans on
http://www.audio-resolution.com/zhorn/herukaplans.html

I don't see a specified dimension for the side walls.

I appreciate all the help here

[Richard Ellis]

I'm sorry I just don't subscribe to this "Ply is superior" notion.
Probably the reason why "factory" speakers are so lame is not that they use MDF, but they use MDF poorly, that is the construction techniques they use are haphazard at best.
I had a firsthand look at factory MDF construction when my prized "Real veneer" RS speakers toppled off the roof of my '70' Mustang........as the speakers hit the ground on the corner of the enclosure & broke apart into its component pieces, I got an eyefull of how NOT to build an enclosure.
The first and most important is panel thickness.........Use one inch......rarely less. Generously reinforce the inside (Whos' gonna see?)
Don't even get into radiasing(sp?) an edge of plywood.........all the voids in plywood make that nearly impossible.
Yes of course you can get the top grade plywood without voids...but it'll cost ya an arm and a leg!
What was once budgeted at $150 for wood, now has just tripled.
Just knock your enclosure with your knuckles.....Got a mic and a scope..what frequency was that?
If it is a high enough frequency then your drivers cannot excite the enclosure and then all of this discussion is moot.
_________________________________________Rick..... .......

[Nanook]

any number of reasons not to use MDF:

• it has a "dead sound
• it's made using formaldehyde, a known carcinogen
• it breathes

MDF can be used if finished on both sides (ie: painted) to help the breathing problem.

I think my second item in the list is enough reason to not use it.

I don't know of any musical instruments made with MDF. To me , that's a test of a suitable material. BB is easy to machine, looks good, is not a carcinogen (that I know of), and can have as "live" or "dead" sound one may want, based on panel construction techniques. It's also relatively inexpensive in Canada and much of the US.

hmmm, wonder why JBL(Pro) has almost always specified Baltic Birch ply as THE material when constructing JBL "approved" pro enclosures?

Every material has a sonic signature of some sort. I just find MDF's signature to take too much way from the music.

gnugear, look here

within the text is mention of the dimensions, which are 8.5 x 14 x 36 inches. Hope that helps.

[Richard Ellis]

So, just what is this "Dead" sound and how does it differ from an "Alive" sound?
Let us cover the mouth with a panel of MDF and see just how one breathes!
Splitting hairs here aren't we?
_____________________________________Rick......... .

[planet10]

Originally posted by gnugear
Do you think thickness matters much? I'm going to use 1/2" for the internal walls and 3/4" for the top and bottom. Just not sure if I need 3/4" for the side walls.

I don't see a specified dimension for the side walls.

That should be fine... he is speccing the wood by the layers, 9 ply BB is 12mm (1/2"), I don't use the Fir ply (at least for speakers) so i'd have to guess 13 or 18mm (5/8 or 3/4")

dave

[planet10]

Originally posted by Richard Ellis
Don't even get into radiasing(sp?) an edge of plywood.........all the voids in plywood make that nearly impossible.
Yes of course you can get the top grade plywood without voids...but it'll cost ya an arm and a leg!

You do need to use void-free plywood. That is all i ever reference (one should keep in mind too that MDF is all over the map, if you have to use it, then use the stuff better classed as HDF)

I'm guess i'm lucky here... The cost of good ply over MDF is negligable (even thou for small cabinets MDF is free) And given the labour involved the cost of the box material is actually small.

dave

[planet10]

Originally posted by Richard Ellis
just what is this "Dead" sound

The sound of all the stored energy covering over the low-level detail that makes the difference between good & really good.

dave