View Full Version : DIY speaker cabinets....MDF or Birch plywood?


streckfu
10-02-2006, 02:47 PM
I've read of both being used so which do you prefer and why (assuming both to be 3/4")?

It looks like the MDF is great to veneer while the plywood would be good to stain.

Any acoustic differences you've noted?

Fast_Eddie
10-02-2006, 03:05 PM
I just built mine with the Birch ply. It's easy to work with and I'm happy with the results. I can tell you this, if you're planning to use the Birch as a finish surface, your woodworking skills better be much better than mine. Think about it: you have to make every cut perfect if that's what you're trying to do. If you're covering with vinyl or veneer you can use wood filler (which I'm planning to do). I'm not sure why MDF would be better to veneer, but it may be. I've heard some say that they thought the MDF was less resonant. I can tell you my experience with MDF is it's not the toughest material in the world. I think long term durability will be better with the birch ply regardless of how you plan to finish it.

Take care,

Ed

Billfort
10-02-2006, 03:45 PM
Having used both and done some comparisons with the same drivers/crossovers in cabinets built with MDF & Baltic birch, the choice is clear for me - Baltic birch.

It's easier to work with and IMO sounds better, at least for the types of speakers I have built. I don't see how MDF would be easier to veneer and since I found building good solid cabinets with clean, square edges a pleasure in bb and a bit of a pain in MDF, I'd say I prefer bb for veneering as well.

I'm not a fan of simply staining bb as it makes cutting the panels and getting perfect mitered corners way too critical. The best technique I've found is straight cut panels with dadoed and rabbeted joints, glued and air-nailed. Edges can be filled if needed and I sometimes leave rabbets a touch proud at the edges for a final clean-up with a trimming bit in a plunge router - gives you a flush, sharp edge that veneers easily.

I have some pics of this technique on this (http://www.wardsweb.org/Billfort/) webpage.

Paul C
10-02-2006, 04:00 PM
Birch ply, by far. I build large speakers that are moved often. MDF is very heavy. If bumped, corners and edges will crumble. Screws do not hold well in it, particularly with large heavy drivers that will be subjected to vibration and shock of transport. I have had customers bring me speakers made of mdf and particle board to build new cabs from ply.

For small bookshelf or living room speakers that will not be moved around much, if at all, mdf may be OK. And for building experimental cabs, the price can't be beat.

As far as "ply has resonances and mdf is acoustically dead" I say "horsehockey". With either material the panels must be properly braced. I have never heard any "resonances" with birch ply.

And you can veneer birch ply, too. For example, Jaymanaa just build those big scoops and filled and veneered over the screw holes that were necess for assembly.

streckfu
10-03-2006, 09:57 AM
I had read some websites where the builder used MDF so I was wondering what it was like to use.

I have no experience with veneer and was only speculatiing if the MDF may be easier. I guess it doesn't matter.

It looks like I'll make plans to use the Birch plywood.

football65scotc
10-03-2006, 10:28 AM
Can the MDF be stained? If so, with what?

streckfu
10-03-2006, 10:37 AM
Can the MDF be stained? If so, with what?


I wouldn't think so. It's just dense fiberboard and would be like staining a thick sheet of paper.

wineslob
10-03-2006, 10:53 AM
Looks like I'm in the minority! I prefer MDF because it's acoustically "dead" ( I can "hear" plywood) machines well, and is great for veneer.

streckfu
10-03-2006, 10:55 AM
Looks like I'm in the minority! I prefer MDF because it's acoustically "dead" ( I can "hear" plywood) machines well, and is great for veneer.


Do you use acoustic dampning materials in the cabinets?

Celt
10-03-2006, 11:00 AM
Thick MDF is acoustically more "dead", but prefer 11-ply Baltic Birch plywood for durability.

streckfu
10-03-2006, 11:28 AM
Thick MDF is acoustically more "dead", but prefer 11-ply Baltic Birch plywood for durability.


I know that it would be a lot more work but would it help to line the inside of the cabinet walls with 1/4" MDF in addition to any otther acoustic dampning materials normally used with the ply alone?

lndm
10-03-2006, 04:16 PM
With either material the panels must be properly braced.
I agree with this statement. Neither material is quiet when large panels are left unbraced.

In my opinion, the MDF has a relatively unpleasant character to its resonance, whereas the BP has a more straight forward sounding resonance.

jaymanaa
10-03-2006, 04:21 PM
I just did some asking around on this very topic. Most folks said Birch plywood, because of workability, and sound. I ended up using Birch, then sanding and laminating with Birch Veneer. I'm very happy with the results. Jay

Filmboydoug
10-03-2006, 07:43 PM
My biggest beef with MDF is when a router is used, it turns into a "1000-times-finer-than-talcum-powder" dust that gets EVERYWHERE!

Fast_Eddie
10-03-2006, 08:33 PM
Can the MDF be stained? If so, with what?

Actually, I have a buddy who made a table that's amazing looking. It has several wood inlays, but one of them is, believe it or not, stained MDF. It looks absolutely fantastic!

Take care,

Ed

Gibsonian
10-04-2006, 06:26 AM
A little more work but you may want to try what I did on my homemade subs. I built the boxes out of birch plywood, 3/4", then cut 3/4" MDF and lined the box with it using screws and glue. All sides are 1.5" thick now. The box is very sturdy and resonance is reduced. As long as weight is not a problem, I think it's a good way to go.

wineslob
10-05-2006, 12:50 PM
Do you use acoustic dampning materials in the cabinets?
Yes, I use polyfill. Most of my cabinets (newer ones at least) sound like a brick ( very high "tink") when doing the "rap" test. The latest ones are incredibly "dead".

lndm
10-06-2006, 04:44 AM
My biggest beef with MDF is when a router is used, it turns into a "1000-times-finer-than-talcum-powder" dust that gets EVERYWHERE!
I reeealy dislike this quality of MDF. May I advise all not to work with it unprotected in an enclosed area. It causes some pretty funky chest/lung pains.

BillEpstein
10-06-2006, 06:09 AM
And some facts.

All the Baltic Birch I've seen over the last few years has 'footballs', oblong-shaped fillers that are used to repair defects in the surface plies. So when I want a good finish I either veneer MDF or buy Hardwood plywood: Walnut, cherry, etc. Most lumber yards don't have it. You have to find the building products wholesaler in your area by asking at cabinet shops. Some of those will order it for you. Good veneering isn't learned in a day and good veneer isn't cheap so the hardwood veneered panels make $$$ sense and save a lot of time.

I recently bought walnut-veneered plywood from China for about 1/2 the price of that from G-P or Weyerhauser, $52 per 4x8 and the quality was very good.

When you buy hardwood plywood also order matching edge-banding 13/16 wide that comes in 250' rolls for about $35. It irons on and covers exposed edges hiding the plies. Of course you hav to figure out which edges will be exposed and tape them before glue up, adjusting the finished size of the box for the thickness of the tape.

Whether you use MDF or plywood there's no reason to use any screws. Screws don't make properly glued joints any stronger. And the torque action of driving them usually moved the panels a bit. You can either clamp w/o fasteners as I do or nail the panels together a la BillFort. Which I also do. It's much easier to fill nail than screw holes. Then cover them with veneer or fill them with color-matched crayons the distributors or most paint stores have. Air nailers and small compressors have become so cheap, and the compressors so useful to have around the house that they've become common. The nail holes from air nailers are much less noticeable than hand nails. Don't bother with 18ga. brads, though, they deflect, especially in MDF. Get the bigger guns that shoot 16 ga. finish nails.

I have no brief on the 'sound' of either MDF or plywood except when it comes to the shelves under equipment. MDF shelves sound hard and etched, solid wood more 'natural'. I've never compared 2 cabinets with the same drivers in both materials and I suspect few others have either. MDF is definitely less durable than plywood as others have stated for cabinets that get moved around a lot. The cheap hardwood plywood sold at home centers is likely to have voids in the interior veneer layers, or worse, loose bits in those layers. The former will show up in veneer eventually, the latter will rattle when you play music.

The Technical Library pages at the JBLPro site has very useful information on cabinet construction and bracing. So do the sites run by Bill Fitzmaurice and Bob Brines. You can find Fitz at the Audio Asylum, if it ever comes back up:) Brines addresss is http://audioroundtable.com/Brines/

You should also visit the American hardwood Plywood site.

Bracing is much more important than the material used. I like what I call 'window pane' braces that brace all 4 sides at once and also help square the cabinet during glue-up:

http://img152.imageshack.us/img152/2896/universityaltecbuild005ba3.jpg

Cabinets up to 18" tall need at least one brace and larger ones, more. Divide the cabinet unequally to avoid panel harmonics.

There's also a lot of opinion and information on stuffing. I use R-13 fiberglass based on the engineering done by Wayne Parham at Pi Speakers. The very expensive "Black Hole" is supposed to be good as well but why spend the money? All you're trying to do is damp resonances around 50 to 100 Hz which the fiberglas does well. There are worries about airborne particles which may be tamed by using fine mesh over the ports. Keeps the cat out, too. I've never tried it but I used to have info on gluing roofing felt to the insides of the panels that does a good job of dampening. The author used an accelererometer and sensitive measuring equipment to get his results. Can't find the site anymore.

You'll all have to be your own judges in the end.

lndm
10-06-2006, 07:47 AM
Are these the articles you mean?
http://www.audioholics.com/techtips/audioprinciples/loudspeakers/mechanicalnoisefloor.php
http://www.audioholics.com/techtips/audioprinciples/loudspeakers/MechanicalNoiseLoudspeaker.php

BillEpstein
10-06-2006, 09:29 AM
That's really good stuff. Actually I was thinking of this:
http://www.silcom.com/~aludwig/Loudspeaker_construction.html

Paul C
10-06-2006, 10:38 AM
We need to differentiate between damping panel vibrations and damping resonances in the interior air. These are two different things entirely.

Gluing material to the inside of the panels, roofing felt, mdf, bracing, choice of construction material, and other methods are used to stop the panels from vibrating.

Lining the cabinet with fiberglass (ugh!), fiberfill, etc, damps vibrations in the interior air, standing waves, all that.

lndm
10-06-2006, 05:27 PM
Extensional damping quite works a trick, too (thats the panel damping without the constraining layer). Ie, lead lining with roofing flashing lead (same precautions as soldering).

It can really quieten a cabinet when done right. You want the lead to bend and warp, producing heat. Glueing it thoroughly to the panel works, but prevents it from moving as much as it could, and it adds mass to the panel. Tacking intermittently with a good adhesive works well.