Making Speaker Cabinets: MDF, Plywood, or Wood?

[JonW]

I’m planning on building my first set of speakers soon. The Modula MT’s, most likely. Many other questions will follow, but here’s a general one: What should I make the cabinets out of? I’ve read a lot (web and books) and see that MDF is preferred. Plywood seems to be coming in second. Regular wood seems to be a distant third. I understand why MDF is good (less resonance), but I guess I don’t have any feel for how much of a difference MDF versus plywood versus regular wood actually makes in the sound of a speaker. Any thoughts on the matter would be great.

MDF:
Easy to work with and cheap. But tons of dust- all over the basement and in my lungs. And I can’t move the table saw outside.

Plywood:
Birch plywood can look nice. A little expensive for the good stuff. And the corners/edges will look a little funny. But no dust. Maybe won’t sound as good as MDF?

Regular wood:
Nothing looks better. Some solid maple and/or cherry… aaaahhhhh sweet. Easy and a joy to work with. Heck, it even smells nice. Expensive. But maybe will resonate too much and sound poor?


Related questions:
-If I go with MDF and wood veneer, what glue do you folks like to use?

-And where do you like to get your veneer from?

-For bracing and reducing resonances, I would think one easy approach might be to just make the whole cabinet doubly thick. Say glue two pieces of 3/4” MDF/plywood/wood together to make 1.5” thick walls. But I don’t see people doing that. Bad idea? Too heavy?

Thanks!

-Jon

[Dennis H]

Solid wood is nice but it can be a problem if the humidity varies much where you live and/or the wood isn't thoroughly seasoned by keeping it inside your house for months before you use it. Wood shrinks and expands more across the grain than with the grain so you can get cracking or joints pulling apart where endgrain meets edgegrain.

[JonW]

Dennis-

I hadn't thought about any of that. See, that's why I asked. Very helpful. So now I'm down to plywood or MDF.

-Jon

[cjd]

Birch ply. Not quite so good 13 ply I've found at Home Depot for ~$30/sheet (which is where MDF is also). The local Menards has started carrying real Baltic Birch (void free) for ~$60/sheet (4x8 in both cases). It's stiffer than MDF and machines well with sharp tools. It's not quite as dense but use of good wall damping (Sonic Barrier from PE, the 3 layer stuff, really does work well) helps there as does bracing.

I would NOT recommend working with MDF in the house at all if you don't have a superb ventilation/dust control system. It's altogether way too nasty.

You can veneer over the birch ply. If you're worried about corners/edging, A little preparation ahead and you could use a hardwood at the ply ends.

Regular wood is probably the least ideal material for the reasons Dennis mentioned. It also tends to be less inert than ply or MDF.

C

[cotdt]

I vote for plywood. It looks great and is easy to make straight cuts than MDF. Solid wood deforms, but I beleive you can treat it.

[JonW]

So you think birch ply is not much of a compromise from MDF? Good to know.

Yeah, it's cheap at Home Depot. A local lumber place has the better "furniture grade" stuff. Prices are about what you mentioned. I'd be happy to spring for the expensive stuff if it would be seen (i.e., not veneered). Except for the edges, it looks quite nice. Or maybe I could use the cheap birch ply and then veneer. Hmmm...

If it's going to be veneered or hard wood added to the edges, is there any reason to stick with birch ply? Maybe use another type of plywood? I guess the lower grade (Home Depot) birch ply isn't anymore expensive than anything else.

What did you mean by prepping to use hard wood at the edges?

This winter I built my first subwoofer. Had never worked with MDF before. (Come to think of it, I haven't done much wood working at all.) It was 20 degrees outside, so I routed the MDF circles in my basement. Oh man. Now I know why people complain about that stuff. I will never get rid of the dust. Never. But I'm also concerned about breathing in all that very fine dust. I just bought a dust mask.

[JonMarsh]

I think the recommendation for Baltic Birch, with sharp tools, is a good one. I gild the lily and usually layup 1/4" HDF on top, sometime in the back, too. It machines well for driver recesses, and helps avoid any splintering. But just ask ThomasW or anyone else around here- they all know I suffer from OCD.

~Jon

[Jack Gilvey]

So you think birch ply is not much of a compromise from MDF? Good to know.

I tend to think of it as the other way 'round. And I think the edges of good void-free Baltic Birch ply are the best part, love the look of the the alternating light/dark.

Just once did I ever work MDF without a mask, felt it for days. Now I use a mask in addition to the built-in wet/dry vac-connected dust collection on my router and table saw. That is, if I have to use the stuff at all.

[jdybnis]

Ditto on the MDF without a mask. Now I only use cut MDF with a mask that has a filter rated for formaldehyde. I'd spring for the Plywood just so I don't have to deal with the risks of MDF dust. One other thing. It's unavoidable to have some cabinet wall resonance if your not willing to make a >150lbs speaker, either way. Good birch sounds better than MDF when it resonates. The coloration with MDF is offensive to the ear, good Birch can actually be euphonic. There is a reason why they don't make musical instruments out of MDF.

[ThomasW]

A loudspeaker isn't a musical instrument, it's a scientific instrument. This means euphonics of any kind aren't desirable.

[jdybnis]

I knew that was coming as soon as I hit submit. I agree 100% with you Thomas. The thing is you can build an acoustically dead cabinet but it is going to be very heavy and/or expensive. I'm not saying euphonics are desirable in a speaker, it's that dissonance is much less desirable. What do you prefer 2nd order or 7th order harmonic distortion?

[ThomasW]

What do you prefer 2nd order or 7th order harmonic distortion?

I prefer no harmonic distortion...:wink:

[jdybnis]

And I want a pony.

(Sorry, I couldn't resist. 8) )

[ThomasW]

Here ya go.....

[Jack Gilvey]

The thing is you can build an acoustically dead cabinet but it is going to be very heavy and/or expensive.

The thing with BB is it's quite a bit more rigid than MDF, you can push the resonances higher breaking up spans with bracing and kill 'em there more easily. I think. I know it works well for subs, you can have a lighter box that rings when knocked but isn't excited by anything in the intended bandwidth, so it's "dead".

[cjd]

All I meant by "prepping" to use hardwood at the corners is all the very careful planning that you would need.

That said, I am quit fond of raw birch ply.

[JonW]

Hey Folks,

I'm very glad to hear you all speak in favor of the birch ply. I'd much rather work with that than MDF. :T And yeah, it does look pretty good raw. So maybe I'd get the good stuff and then just add some finish. Or maybe the cheap stuff and try veneer. Not sure yet. Hmmm...

To eliminate cabinet resonances, wouldn't just making the cabinet twice as thick help? Say glue 2 pieces of 3/4" birch ply together. In addition to bracing, etc. That could make for some really solid corners, too, with effectively a 3/4" rabbet. Or does that just make things too big and heavy?

[cjd]

The big towers I did are two sheets of 1/2" laminated for the main box, 3/4 for the baffle (3/4 for bracing).

The bottom pic is a Tumult, which is two sheets of 3/4 laminated and a 3/4 roundover.

I can not imagine how heavy any of that would have been in MDF!

Good bracing goes a really long way to an inert box.

C

[JonW]

OK, right. So I can see lots of layers in the sub, when I count. Right. So I guess some people do double layer things. And you did both double layers _and_ internal bracing as well, correct?


Your raw birch ply cabinets look nice. From the photos, the lighter color of the tower blends in with the edges better, I'd say. For the MTM's, you maybe stained them a bit (?) and the edges stick out more. Maybe raw birch ply (or stained lightly) is a way to go... For some furniture things I might try to make (now that I'm collecting power tools) raw birch ply should look quite good.

[Brian Bunge]

Hey, I'm just happy to announce that two weeks from now I will have my tools moved down here and will be able to actually build something again!

I can't tell you how thrilled I am! WOO HOO!!!

[cjd]

Are your speakers home yet? :P

Jon: The big 3-ways are raw, unfinished.

THe light MTM's are tung oil finish.

The dark ones are an ebony stain.

C

[Brian Bunge]

Chris,

Nope, none of my A/V equipment is in FL yet. But I will have it all setup and ready to go in a couple of weeks!

[kramskoi]

how's this for a dead cabinet...

the enclosure for a Tumult 15". Another 1.5" of front baffle has since been added.

[ThomasW]

Thick is good.

You'll need to check if back-beveling is necessary to keep the thick baffle from obstructing the rearwave off the cone

[Dan B]

Did you say basement?

I work with MDF just in front of my garage and its a mess, a basement would be horrible.

Almost everything I had read up to this thread recommended MDF, and thought plywood was a serious compromise. Maybe I should give plywood a shot.

[Dan B]

If my speakers resonated like that cheap guitar I had as a kid I would be bummed out.

I work with MDF just in front of my garage and its a mess, a basement would be horrible.

Almost everything I had read up to this thread recommended MDF, and thought plywood was a serious compromise. Maybe I should give plywood a shot.

[ThomasW]

If my speakers resonated like that cheap guitar I had as a kid I would be bummed out.

Nothing made with 3/4" or thicker MDF is going to resonate like a cheap guitar. The stuff is just too damn heavy....

[Dan B]

I meant the plywood.

Nothing made with 3/4" or thicker MDF is going to resonate like a cheap guitar. The stuff is just too damn heavy....

[ThomasW]

You'll find that 13 layer BB ply is virtually a heavy as MDF. And BB ply's Fs is higher than MDF. Where BB ply 'wins' is the ability to use a single braced layer of it compared to multiple layers of MDF

[---k---]

I got a little confused reading this thread, because it seemed like people were using terms interchangably. It is my understanding that there is:

1. MDF - Good stuff, heavy, nasty to work with.
2. Void Free Baltic Birch Ply - Really Good stuff, lighter than MDF, need sharp tools to work with, but more expenisive than MDF and usually only found at real lumber stores and not HD or Lowes.
3. Baltic Birch Ply - Found at Home Depot and Lowes, has some voids in it that will may make it resonate a little more than the MDF and Void Free.
4. Regular Plywood -

1 & 2 are what I generally see highly recommened. Someone else can maybe clarify the compromises involved in using 3 & 4. I'm also unsure is the Void free is the 13ply BB, and the with voids is less, or what.

[Dan B]

Thanks!

I sure get no joy working with MDF!

[ThomasW]

The void free plywoods are the 13 layer plys, so Baltic Birch, what's called Apple ply, there's a 3rd one that escapes me at this time....These are the good stuff and they work well when used in a single 3/4" layer box with good bracing

Standard plywood, 5 or 7 layer whether it has a birch outer layer or not should be avoided

[cjd]

Baltic, Apple, or Marine (think that's the third) Ply should be void free 13 ply 18mm (3/4"). They're pricier. Menards seems to be carrying this in 4x8 sheets around me.

You can get 13 ply that is NOT the above three in 18mm. It's cheaper - about half the price, and about the same cost as MDF.

At least, that is my experience.

C

[JonW]

I work with MDF just in front of my garage and its a mess, a basement would be horrible.

It was 20 degrees outside the weekend I cut the MDF circles for my sub. Couldn't do that outside. So yeah, I did it in the basement. I had no idea what "dust" really meant, but I sure do now. But I'm glad to hear that I can happily work with Birch plywod from here on in. Much nicer to deal with. :T

[JonW]

Birch ply. Not quite so good 13 ply I've found at Home Depot for ~$30/sheet (which is where MDF is also). The local Menards has started carrying real Baltic Birch (void free) for ~$60/sheet (4x8 in both cases).

Is my understanding correct that both of these are OK for building a speaker? Same density, stiffness, etc. Just the cheaper stuff isn't as pretty. So if I want to veneer, go for the $30 cheap stuff. If I want to look at the birch when I'm done, do for the expensive version. I think they call the expensive stuff "furniture grade" and the cheaper one is "paint grade."

[ThomasW]

If you use plywood it should be the 13 layer ply....

[JonW]

If you use plywood it should be the 13 layer ply....

No problem. Thanks for all the help. :T

[Dennis H]

Is my understanding correct that both of these are OK for building a speaker? Same density, stiffness, etc.

I think that's a hasty assumption. The nearest HD is about 50 miles so I can't check it but I'm skeptical of the cheap price. The real stuff uses hardwood for all the plies. I'd be willing to bet the cheap stuff uses softwood for the interior plies with a birch veneer. It may or may not be void free inside. If all that's true, it would be lighter and not as stiff, even though it has 13 plies.

It would probably still work okay but it wouldn't be the same thing. Of course, it wouldn't be the first time I was wrong.

[cjd]

The cheaper stuff is NOT void free. Clearly not.

I am not sure what the core is. It doesn't look significantly different at first glance - I would not hesitate to use it for cabinetry where less-than-perfect materials are needed, just the stability of the 13 ply stuff. In fact, I just built myself a desk of it.

C

[knifeinthesink]

mdf is evil. even with a dust mask i feel like i have the flu the next day. Blech! Cheap and easy to use though, which is at least part of the reason people keep using it.

There was a good article on bracing in audioXpress not long ago. Basically, in a deep tower best results were to be had with three vertical braces running the length of the cabinet attached to the side panels. Least effective was bracing horizontally since it had the effect of creating square sections that were suseptable to greater sympathetic motion.

here some interesting info on cabinet materials from al ludwigs site. this configuration is the one im currently sold on. yet to try it myself though. Link is at the bottom if you want to see the charts.

Constrained layer panel

3/4 inch mdf/2 layers #30 roofing felt/1/4 inch masonite

The red curve was the first test, where the inside of the large enclosure was empty (except for the old loudspeaker), and the top was 3/4" MDF. The blue curve represents the same configuration except that the interior was filled about 50% with fiberglass (the garden-variety type used to insulate houses). The fiberglass filling reduces the panel vibration by about 20 dB across the entire frequency range. This corresponds to absorbing 99% of the sound energy, at a very low cost, and with very little effort. And it kills internal standing waves. The lesson here is real clear: stuff the enclosure with fiberglass. All remaining tests included the fiberglass filling. The black curve is for 3/4" MDF plus a layer of 1/4" tempered Masonite, but no damping layer. I was again surprised that adding this layer didn't improve things more than it did, but this was probably because the two layers were only attached at the edges by the array of bolts. If the two layers had been glued together I think there would be more improvement. The final two curves are for the full sandwich with the damping layer. The damping layer for the cyan curve is 1/8" loaded vinyl that costs $2.00 per square foot. The damping layer for the green curve is 2 layers of 30# roofing felt that costs $0.17 per square foot (thanks to Dickason for mentioning this stuff). The constrained layer of roofing felt reduces the peak vibration by almost 20 dB, and the average by about 10 dB, relative to the blue curve without a damping layer. In most regions it is better than the hi-tech pricey vinyl. Needless to say, I chose the roofing felt sandwich for my enclosure construction.

Pasted from <http://www.silcom.com/~aludwig/Loudspeaker_construction.html>

[JonW]

I think that's a hasty assumption. The nearest HD is about 50 miles so I can't check it but I'm skeptical of the cheap price. The real stuff uses hardwood for all the plies. I'd be willing to bet the cheap stuff uses softwood for the interior plies with a birch veneer. It may or may not be void free inside. If all that's true, it would be lighter and not as stiff, even though it has 13 plies.

It would probably still work okay but it wouldn't be the same thing. Of course, it wouldn't be the first time I was wrong.

The cheaper stuff is NOT void free. Clearly not.

I am not sure what the core is. It doesn't look significantly different at first glance - I would not hesitate to use it for cabinetry where less-than-perfect materials are needed, just the stability of the 13 ply stuff. In fact, I just built myself a desk of it.

C

Hmmm... Interesting. So maybe it's not the same, just different "prettiness." Any way to figure this out for sure? It would be silly to pay twice as much for the good stuff if it's just going to be veneered anyways. Unless they really are different.

cjd-
If I was making a desk out of the stuff, that's when I'd buy the expensive version. From what little I've looked at the birch ply in stores, the $60 version seems to be just prettier to look at. It's a small change versus the $30 version. But a desk has lots of surface area to look at and touch. For that (or anything else that won't be veneered), I'd get the good stuff.

kinfeinthesink-
Excellent link! I'll have to read it over in more detail later. But that should help me design my cabinets.

[cjd]

The dfference between the cheap and the expensive is NOT the surface veneer - both look great. It's the core. The cheap stuff is not void free, for sure. It *may* be a different material as well, but I do not know this.

Once again.

The cheap stuff is not uglier. it is just as pretty (except perhaps the edges, which is easily taken care of with filler). The surface veneer is still grade A, smooth, etc. And it is not as well suited to speaker cabinetry, because it is not void free.

C

[thylantyr]

Here is my take on the wood issue, it's very simple.

* If you are a skilled woodworker you can use nearly any type
wood to make speaker boxes. I can make a subwoofer box out of
balsa wood because I know how to get around the issues. :wink:
I can also make a box without using wood! ie, cloth skin with
fiberglass layers.

* Application: Subwoofer cabinet? midrange cabinet? Front baffle?
Bracing? Strength? Mass? etc. You can use different types of
wood if for different applications.

* Money: Sometimes people just don't want so shell out $300
for a 4x8 sheet of esoteric plywood so there are alternatives just
as good.

* Mobility: If you plan to haul the cabinets around often, the
choice of wood influences the design, ie for prosound cabinets
and touring, the choice would be more obvious than an esoteric
home speaker design.

[thylantyr]

Constrained layer panel
3/4 inch mdf/2 layers #30 roofing felt/1/4 inch masonite

Childsplay.

Try 1.5" MDF {laminate two 3/4"}, or three layer MDF for
2.25". I'm fond of 6 layer - 4.5", it's pretty dead in sound.
-> Install proper bracing

Ultimate dead = coffin speaker box

[JonW]

The dfference between the cheap and the expensive is NOT the surface veneer - both look great. It's the core. The cheap stuff is not void free, for sure. It *may* be a different material as well, but I do not know this.

Once again.

The cheap stuff is not uglier. it is just as pretty (except perhaps the edges, which is easily taken care of with filler). The surface veneer is still grade A, smooth, etc. And it is not as well suited to speaker cabinetry, because it is not void free.

C

OK, got it. So I'll have to pony up for the expensive stuff regardless of what I'm making- a speaker for veneering or a speaker without veneer. But for some simple furniture, the cheap stuff will be OK. I was going to do the opposite, so I guess this discussion has not cost me any money.

I've never worked with either (if that wasn't obvious). When looking at the cheap stuff in the store, the surface layer somehow seemed less nice (more porous, less regular) than the surface layer of the expensive version- in a different store. I guess it's just like trying to compare different speakers in different stores.

Thylantar-
Thanks but I think that I'll try and avoid both the balsa and the coffin as best as I can.