Why use 3/4 Birch vs. MDF

[Dylanl]

Why do people use 3/4 birch instead of MDF. Plywood always seems to have voids MDF is so solid. The only problem I can see is weight. What do you think.

[Good2BHome]

Most importantly MDF does a very poor job of holding screws, particularly into the edges.

The plywood used by Klipsch, Baltic birch, is known for not having voids.

[ricktate]

Try dropping or bumping mdf on the edge and see what happens,the plywood is much tougher. I dont think some of these 35 year old K-Horns would still be around if not made out of plywood. I know the ones i got had a tough life but still held up real well.Rick

[D-MAN]

Plywood is sold on a void-free basis, that is, it is a particular class of plywood. Marine grade, for instance, is voidless, as are some others. It's a specification.

MDF cannot take a screw from the edge, its main drawback.

While it does not have voids, it is not the same strength overall as ply. It has a much lower stress breaking point.

Theoretically, the random grain structure of MDF or HDF is less prone to vibration transmission, but it lacks lateral strength. Plywood on the other hand, has continuous grain structure but alternates the direction of grain between layers. I think that means its a wash.

I prefer a good void-free 7-layer exterior (at least) plywood, but it depends on the application.

DM

[Dylanl]

Why do you need screws? Most cabinets if done properly are mitered and glued, no screws. My RF7's are MDF veneered. I looked at a prior post only found 1 on MDF but many agreed that sonically the MDF is better. The density cuts down on standing waves. They also stated corner damage could be an issue. The speakers I am building will weigh approx. 140 each. You can also get MDF in 1" at a fraction of the cost of plywood. One mod that would really help the Cornwall and LaScalla side walls. Wonder why Klipsch did not use 1" ply? I bet it was cost.

[Tom Mobley]

Dylan,

Might want to think this over some. Most of the joints are glued and screwed or nailed, some angle joints would be difficult or impossible to clamp while glueing. Also, if you change from 3/4" to 1" it will affect the plan dimensions considerably. You don't need 1" plywood. Keep in mind that the weakness of MDF is poor tensile strength around the corners and edges. Even if you use glue and clamp with no fasteners it's an edge joint.

MDF is really dense, but it's difficult to work with. Even the sawdust is a PITA, it's fine like face powder. Nasty. It's also hard on tools and blades.

I have over 10 years experience working in the plywood mills of Oregon and Washington, I worked all phases of production, mostly lay-up of the panels themselves. AFAIC, that baltic birch plywood is top-notch stuff. It's very dense compared to regular plywood because the plies are much thinner and all the plies are birch hardwood, not just the face and back coverimg softwood plywood like normal.

And MDF? Well, it's particle board. Compressed sawdust.

BTW, I have a layout I made to construct a Belle out of two 5' x 5' panels of baltic birch. Is it a Belle you're building?

[D-MAN]

Tom is absolutely right.

Also for complex high strength structures like a Khorn for instance, screws are best used rather than nails. Anywhere where vibration might work out nails, screws are better, too. There is alot of edge mounting in the Khorn and other complex cabinets, which MDF would not be appropriate for.

DM

[Dylanl]

Tom, I am thinking about building the Altec model 19 or the LaScalla with the ported option. The Altec plans call for 3/4" MDF. I do not have a problem working with Birch, MDF it's just what the plan calls for. Is the wood that you purchased for the Belles from Home Dept or Lowes? They carry a 4' x 8' for 49.00 sheet.

[Dylanl]

Tom, if you would please send me that layout I would like to look at it. Send it to: Artvandelay1@peoplepc.com The reason I stayed away for the Belle was because of the frequency range. I want a speaker that is lower in bass.

Thanks

[colterphoto1]

You tell em Tom. Any particle board or MDF, they may have well just kept chipping it up until they made hamster bedding. Not worth building out of IMHO. All that glue means it's heavy and it won't hold any type of fastener. BTW, your Belles are ART!

Michael

[WMcD]

I use birch ply and don't intend to change.

I do get annoyed at the quality of birch stuff at HD, such as I bought last weekend. The "classic" stuff from China looked good but the top veneer was not glued on very well and tore off in spots while cutting. Grr.

It is for a not critical application (speaker stands to be painted) and I got what I paid for. I could have paid for better stuff.

It is a shame that HD sets up the stacks on the canilevered supports in a way that thousand of dollars worth of wood gets a mild twist or warp.

Wood World in Plano has excellent plywood if anyone is in the Dallas area. Not cheap, but first rate. In my view, there is so much labor involved in home projects that tempermental material just drives up the frustration level and overall cost of time and effort.

Naturally I agree with the comments above about MDF. Granted, factories can work with it. And if the bottom line depends on material costs, they must. Even when the assembly can be made well, there are shortcomings delegated to the owner.

I had to change out a diaphragm in the Ebay Quartets. The boxes are made of MDF. The screw holes for the horns are fragile and the threads of the holes, such as they are, turn back to saw dust. Superglue helps a bit to solve the problem.

The units suffered shipping damage at the corners. Again, it is partially a matter that MDF is sawdust and glue.

Then there is the potential water damage issue. Ply stands up pretty well. Any MDF swells and the object is worthless.

My rant.

Gil

[Jim E]

Brett,

The LaScala's have the same bass response as the Belle's according to all the literature I've seen as well as the posts on this forum. The "ported" LaScala looks like an interesting project, but I've only seen a few posts on them. Taking these posts into mind it would appear the same modification could be made to the Belles. Perhaps the original poster could comment on this.

As to the use of MDF Vs. Plywood...they each have their uses and both MDF and plywoods come in different grades. I have seen what Home Depot and Lowes offer and I can assure you what they sell is not what you want. Neither outlet sells a decent grade of plywood much less high grade appleply,birch or marine ply.

Cabinet grade MDF with A1/A2 veneer facings work very well in constructing bass reflex and sealed cabinets. Ply as used on the Klipschorn, Belle and LaScala is very appropriate because of the manufacturing process Klipsch employs. I recall reading on this forum that Klipsch does use some MDF in the later Heritage cabinets.

Just my opinion.

[colterphoto1]

Woodworkers hint for stripped screw holes:

Remove splintered fragments.

Fill hole with wood glue.

Cut several toothpicks or kabob skewers the depth of hole.

Cram em in- leave a little void as area for screw to start.

More wood glue.

Let dry.

Sand off flush with board.

Voila, new 'bite' for wood screws.

BE GENTLE.

[Tom Mobley]

Dylan,

I've never scanned those cut sheets. I drew them out to scale on graph paper, need to clean them up, scan and post. I'll try to get time tonight.

[tgw323]

I disagree totally with the statement that Water will make MDF swell and break up. This refers to MDF I purchased at HD. I had a project that I needed to do wet sanding on. Searching for a make-do sanding block,I spied some pieces of scrap MDF. I thought,well if it falls apart, there's plenty more where that came from. This same piece of MDF was in and out of the bucket for days at a time. Months later,I measured it with dial calipers and it hadn't swelled at all.

[Marvel]

I believe that djk indicated you could do the same bass mod with a Belle. I've just worked on the drawings for the LS and tried to compile the info. The Belle is shallower (front to back), so it might pose limitations on the internal volume depending on how you wanted the end product to look. On an LS you can make it totally invisible, so it looks like a stock LS to the most people. Obviously, there are ports on the back, but from the front you wouldn't see a diff.

Marvel

[STL]

tgw323,

I think some people are confusing partible board and MDF. They are NOT the same!

[SCOOTERDOG]

The biggest challenges associated with using MDF is the cutting and screwing of the material as noted above. I for one choose to use birch any day. 1st if yo are building speaker boxes using birch then void free is the only way to go. 2nd enternal bracing is a key to keep the cabinet from resonating. This is an area that can not be overlooked. Yes MDF is very dense materail but a bit#h to work with for most DIY projects. Attached is a pic of the enternal bracing I did when I built my center. If you do decide to use MDF then make sure ventilation is good and wear a mask....nasty stuff

scooter

[STL]

I use MDF myself. I admit it's harder to cut and rough on blades, but I found a local lumber yard that has a mill shop that would do precidion cuts for me. I had two 49"x97" sheets of MDF cut (with almost no scrap left over) to my specs for only $60 delivered. That might sound like a lot to some, but it saved me A LOT of time and work -- not to mention if any of the cuts came out wrong THEY have to make it right. With the MDF, I made this center channel speaker:

, this subwoofer:

, and two of the rear speakers:

.

While screw holes could be a problem if you plan to remove/replace drivers a lot, but I don't think it's near as bad as some people here try to make it -- at least not with the MDF I used.

[STL]

BTW, I screwed and glued the joints. I used clamps to hold the pieces in place while I pre-drilled a hole for the screw. The bit I used also counter-sunk the hole for the screw heads, and I just used cheap dry-wall screws (with the fine threads). I didn't have any problems with the edges chipping.