Speaker construction

I'm about to begin purchasing the components to build my own speakers. Unfourtuately I don't have tuns of money so I can make them out of MDF like I would. They will most likely be made out of 3/4" Maple veneered plywood. What I'm wondering is whether biscuiting the joints would be an addequite way to construct them. I wanted to build them with no screw holes etc. I don't have a place to post any pliminary desgins, is there anywhere to? Any help would be great as. If you can poit me to some good sites I wold be greatful.

Thanks

Jeremy Hopkins
 
Jeremy,
Actually, MDF isn't that expensive--about half the price of veneer plywood. Around here Lowe's and Home Depot both carry 3/4" in stock. Maybe it's just because they know they can sell it to me...
Biscuit joints should work okay, but be sure to caulk inside as I wouldn't guarantee that they will seal air tight. Why not use a router to form rabbet joints?

Grey
 
Jeremy,

About the biscuits - I'm only fifteen but I have built my own speakers before. I have constructed boxes out of both plywood and MDF, and might I add, the MDF is infinitely better. I would strongly suggest NOT using just biscuits, if you even use them at all. Plywood can sometimes splinter and crack when you cut into it on its side, so you dont get a very clean hole. A layer of MDF can often flake off sometimes as well. Also, if you were to use biscuits, it can be very difficult if the wood you are working with isn't wider than an inch. You just can't get a sufficient amount of strength using biscuits in this case. The use of screws and carpenters glue would be much better, and as I've done with MDF, a wood filler and a belt sander can make the sides very smooth, so that you can paint or veneer as you choose (although I've had some bad veneering experiences :p). If you're doing a smaller set of speakers, several coats of lacquer based spraypaint looks excellent, but the MDF soaks it up like a sponge. Hope I've been of some help.
 
MDF from a woodworker

Okay, take some advice from a woodworker. Go with the MDF, it should be cheaper than the plywood you're buying AND you'll be much happier with the results. As to the use of biscuits, they don't actually add much of anything to the strength of the joint, and with MDF, you run into a very real possibility of having the stuff swell up right around it because of the water in the glue. The best way is to use the screws designed for MDF, wood glue and simple butt joints. Then, after the fact, you can caulk the inside edges/corners to insure an air-tight seal. Also, you might want to try shopping around a little bit for prices on the MDF, look in the yellow pages under lumber yards and see who else is in the area, you'll find a wide range of prices and quality around. (Yes there are different degrees of quality in MDF)

I also agree with Super about the stuff soaking up paint. (Remember, this stuff is basically wood dust) Oh, and you might want to think about either a respirator or a well ventilated area when cutting it. (Its extremely dusty!!)

Good Luck with your speakers!!!
 
Go for MDF, - it most definetely gives better control over resonances than chipboard, or even worse- plywood.
An old painter's trick is to use one or two layers of high gloss paint or lacquer first, and matte it down before continuing. High gloss paints has a higher surface strength when wet, and covers the pores better instead of sinking in.
A good layer of filler/primer is of course the ideal way if one's using lacquer or paint. If there is bare or sanded/profiled MDF corners, primer/filler is mandatory in order to get a perfect result. It is cumbersome and time consuming, but done the right way, it can give you a finish to be really proud of, -- like a polished Grand Piano....

Another trick for neat corners is to brace all the joints with timbers ( and lots of glue..).I use 1x2" for medium-larger boxes... 1/2 x 3/4 should do for smaller boxes. End the panels edge to edge attached to the timbers, and then fill in the corners with "1/4-staff"-1/4 round trims to fill the gaps.The joints should be reinforced with timbers anyway, because it gives a stronge3r joint and thus disperses the energy away from one single panel over to the others, and thus lessens the single panel resonances. All panels should of course also be cross braced, to short curcuit panel resonances, if you don't use multicell structures ala B&W and others.
Good luck
 
Why MDF?

Everyone makes speakers out of MDF, why? I have a good woodworking shop and I like oak. Most of the trim and furnature in my house is oak because of my predisposition.

So, why not build speakers out of oak? Is it just price? I realize a good sized cabinet made of oak could be $50-$80.

I thought the stiffer the better for a speaker cabinet. There are few woods harder than oak.

For me, the wife acceptance factor is very high. A painted MDF box would be in the dumpster before I could try it.

pixie
 
MDF

Pixie

MDF is an inexpensive, heavy material that is easy to work with. The fact that a wood is hard is good, but it is not necessarily THE most important factor when considering your material. The weight of MDF has good dampening capabilites, and as to whether or not there is any validity to this statement, from past experiences I have had an easier time dampening and dealing with acoustic variables when using MDF rather than oak or other hard woods.

Basically, it is heavy and dense, giving it good ability to dampen acoustics. It is easy to work with, inexpensive, and it can still be finished to your liking via paint or veneer.

(By the way, a look that I tried on one of my speakers was a black lacquer finish on 5 sides, with a light birch finish on the front. It looked very classy, yet contemporary.)
 
MDF superiority

What really counts for speaker boxes is the so called elasticity module of the material involved. This tells a lot of the material's ability to vibrate.
It is fairly common knowledge that a loudspeaker made out of "wrong" materials can radiate almost as much sound from the panels themselves as from the actual membranes. Such a situation makes all fancy calculations of x-overs,radiation patterns and intensities worthless. What really happens is that the energy inside the box puts the panels into oscillation, and the sound we hear is the sum of the membrane and panel radiations. When excited by an energy source, here the driver elements, all panels will resonate or swing, both longitudinally and transversly, just like a guitar string. Worst case situation is when you have a square panel which will have the same freq. in both directions. Then imagine a cubical box, where the remaining 5 sides will all have the same resonance frequency.....
The resonant freq. will depend on mass and stiffness factor, but the decay time will depend on the materials elasticity factor. In real terms, it is a rather complicated symphony of the different parameters involved.
A steel plate is a good example of a highly resonant panel, a rubber panel is a very elastic and damped one. A concrete panel has very high mass and some elasticity, and is therefore one of the best materials available. Its drawback is of course things like weight, "workability", and stuff like that. For woods, MDF is fairly elastic, has medium density, but very little "inner tension". An MDF panel sounds fairly "dead" when you tap on it, in fact the more procounced "tone" you can hear when tapping the panel, the less suitable for loudspeaker boxes....try knocking og panels of MDF, chipboard, plywood, or any "solid" wood panel, laminated or not, and you will litterally hear what I mean...This is also why the diagonal bracing of panels is so important, as it will to some extent "short curcuit" or dampen the resonances. Real wood panels, or prime quality plywood gives great looks, but high resonant panels which albeit can be damped by proper means. Concrete boxes, mineral filled epoxy panels or moulded boxes( e.g. Wilson Audio ), double cabinets with great outer looks of e.g plywood with a thin but packed sand filling inbetween are our best alternatives today, if you are pursuing the perfect.Matrix cabinets are also a very good solution indeed. The rest of us have to compromise, and use mostly MDF. SAF or WAF is indeed a highly governing factor for most of us...so veneer or lacquer it will be....
 
Pixie,
Hard isn't the question. We're not looking for hard. What we're looking for is dead, i.e. non-resonant. Oak is hard, but is resonant.
I build basses from raw sawmill planks of exotic hardwoods. One of the things I do is search out the hardest woods I can find, and the most resonant. Oak is nothing compared to the ebony (or rosewood) I use for fret/fingerboards (depending on whether the bass is fretted or fretless). Wenge, bubinga, purpleheart, etc. are some seriously hard woods. Yes, I've used flamed red oak on the body of one instrument. (Only board I've ever seen like it...absolutely beautiful.) Anyway, the point is that I glue up neck blanks of laminates of various woods with the grain pointing in different directions so the resonances cancel, but the hardness and stiffness remain. Unless you go to extreme lengths to cancel the resonance in your oak, you're going to end up with a cabinet that 'hums along with the music.' Think of it as harmonic distortion--a tone that comes out that was not what you put in. Speaker-produced distortions are bad enough (on the order of entire percentage points--horns are even worse) without adding to them by building a resonant cabinet.
Brief digression:
Traditionally, the American philosophy has been to use really thick sides, and brace the hell out of it, seeking to stop resonances before they start.
The British philosophy was to use thinner panels, frequently unbraced, but damp the panels with bitumen or something that would dissipate the vibration as heat.
Over the years, the American strategy has gradually gained acceptance; don't let the resonance even start. Extreme cases include making the speaker cabinets out of Lucite, aluminum, glass, or even concrete. (There was a non-trivial segment of the horn community who felt that the one and only way to build a horn was out of concrete. The fact that this meant that the speaker was an integral part of the house was irrelevant.) Other variations include double wall construction, filled with sand or lead shot...you get the idea.
Don't think hard. Think dead.
Incidentally, particle board isn't as bad as some people make it out to be. It's actually fairly dead. The problem is that it does tend to chip out. It also frequently includes sand and bits of metal and such that tend to wear out saw and router blades unnecessarily quickly. Ever notice a spark fly when you were working particle board? You just hit something in the wood.

Grey
 

Harryo

Member
2002-02-28 10:05 pm
I've noticed no one even mentioned acoustical plywood. I'm assuming that it's still made.
(been some years since I've built an enclosure.)
I used to use 7 or 10 ply acoustical plywood usually made of birch. (just what is used in the klipshorns.)
thickness is usually 7/8-1-1/4 thick as I recall.
I'd line most of the vented boxes with poly-fill if any dampening was needed and always got fairly good bass response with little or no resonance.
I've also constructed concrete horns built right into the house. (started out in the basement and built up into the listening room or studio. massive horns to say the least!)
I'm thinking of building a few enclosures just to stay busy and will be weighing in a lot of what was posted here.
Has anyone tried experimenting with laminating various materials together for a more rigid/dead panel?
I'm thinking of 2 layers of MDF with a center layer of either lead or concrete. (combined thickness around 1-1/4 inch.