Dumb Box Building Questions

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Redeye

Member
2002-08-22 1:44 pm
London
Hi folks.

I'm in the process of designing a couple of pairs of speakers at the moment - one passive pair, one active pair. I know plenty about the acoustics and electronics stuff involved but I don't have so much experience on the woodworking side. I'd be grateful if some of you guys could help me out with a few of the dumb questions I've got :

1. I'm planning on using MDF around 20mm (depending what they've got in B&Q when I go). I was also planning on putting the whole lot together with the glue + screws approach, which I was hoping to do in a way which avoids me needing to clamp while the glue dries. Are there any tips you can offer me on this method?

2. This sounds really dumb, but is there a recommended way to put the 6 panels together ie. which order to put them together, which panels overlap each other in which ways? I guess I should mention that I'm probably going to use a single internal bracing. Does this make life much more complicated?

3. Are there any websites with useful pictures about the actual box construction itself?

I'd really appreciate any advice here. Thanks in advance.
 
Screws and glue work well as long as you pre-drill the holes with the appropriate sized bit. Use #8 x 2" coarse thread bugle head wood screws and use a 9/64" drill bit, preferably with a countersink. Regular wood glue is fine as long as your cuts are good.

Panel cuts/assembly is usually:

Fronts and backs are full width and height.
Sides are full height.
Top, bottom and dividers are all inset.

Attach top, bottom and dividers to one side.
Attach the other side.
Attach back.
Attach front.

Baffle can be pre-cut with driver holes or done after assembly and finish, whichever you prefer.

Pete
 
Pete Mazz said:

Baffle can be pre-cut with driver holes or done after assembly and finish, whichever you prefer.

Pete

I strongly suggest to cut holes before assembly since you will not have to destroy the box if you make an error.

Also, for the speaker hole, you should practice on a piece of crap before cutting the real piece

I am talking from experience here, hehehe :)
 
Redeye said:
1. I'm planning on using MDF around 20mm (depending what they've got in B&Q when I go). I was also planning on putting the whole lot together with the glue + screws approach, which I was hoping to do in a way which avoids me needing to clamp while the glue dries. Are there any tips you can offer me on this method?

This is how I usually put my boxes together (don't have big clamps), and it works well. What I do is assemble the two pieces that I'm attaching, and sit (carefully!) on the assembly while screwing into the pre-drilled holes. Hold a big square against the joint to keep it alligned properly.

Good luck, Dan
 
glue and screws approach

Just a quick note for all of You not using clamps but the glue and screws approuch:

If You don`t care much about a nice and professional looking finish of Your speakers You may do so but whatever You want do after the box building process - be it spraying or veneering - the srew heads will come through the surface after a while - no matter what and how careful You do to hide them.
Believe me - I made a couple of dozens professional (looking) enclosures in my life already - don`t even think about that You can avoid it though.
The clamp method is still the best in this regards.
 
Maybe the best thing is to use the screws to assemble the box, then remove them when the glue has set. then fill the holes.
Mark:
That`s a good idea but I have tried this one before also. This looks fine some weeks or maybe even two month but the holes will come through sometime finally (I even tried many different materials to close the holes: wood cement, laquer putty, epoxy, wood plugs..... no chance).
That`s particular true when You spray but even with veneer this happens unless You use thick (3-5mm) sawed type veneers. The usual thin (about 1mm and less) sliced veneers will not prevent the holes from coming through.
As I said: don`t even think about it........(if You are not satisfied with something less than perfect - and I know many of You won`t).
 
On a side question, how do you guys do your really nice boxes? I've never checked how the pros do theirs, I just route groves so that they fit together snugly, the glue and clamp, it turns out really nice for the look and I can jump and stomp on the boxes without any harm, so I'm happy. I'm just curious about other methods.
 
alternative to srew clamps

I forgot to mention:
If You don`t have access to real srew clamps the next best thing is to use clamping belts. Those things used for instance zipping stuff at the roof luggage rack of a car - if You know what I mean.
There are rugged versions with a tightening mechanism and one can get a fair amount of pressure with them. Also these are easier to apply for a single person (with srew clamps sometimes You`ll need a third hand).
Since finishing nails are rather thin, the marks from them were negligble (comparing to screws).
I use the finishing nails to fix the panels too (that they don`t move from the right position while glueing) but I cut them and apply them at the "inside" area where the glue is to be applied. As they only are for fixing even no need to hammer them through the panels (and the hassle to remove them again without hurting the surface).
 
Can I clear up a little misconception here, if panels are cut true and square, very little pressure is needed to assemble joints.

Contrary to popular opinion,normal white or yellow wood glue does not have to be squeezed right out of the joint, in fact, this makes the joint weaker, as less glue remains to fix the parts together.

If the panels are well machined, then ordinary gaffer, (duct tape for our transatlantic cousins) will put enough pressure on a joint for a good result.

Now if your panels are out of true, that's when clamps or screws can be used, but with only enough pressure to bring the joint closed, not so tight all the glue is squeezed out.
 
Thanks for the advice folks. I've just been handed an extra incentive for this project by a guy at work who doesn't believe I can design and build a set of speakers that sound better than I could buy for the same price.

I think I'll stick to the glue and screws approach to start with and put the aesthetics as a lower priority for now, although I take your point about it making it a lot harder to make them look good.

Going off on a slight tangent here, what finishing methods (painting etc.) work well on MDF? I've really not thought about this too much yet - I'm much more concerned with making them sound good, but I guess it's worth bearing in mind.
 
Hi Redeye,

You should also consider chamfering the edges of the front panel. It helps to minimise the edge diffraction effects and improves imaging. To do a professional job you really need a router for this but I have done a pretty decent job in the past with a hand plane, sandpaper and a lot of effort.

You should try and find a builders providers for the MDF. B&Q are expensive in my experience.

You can also get veneered MDF. Comes with a sheet of veneer already glued to one side. Could make life a lot easier for the finish but you would have to mitre the corners to prevent the edges of the MDF sheet from showing and you can forget about my first suggestion of chamfering the edges.

BTW what sort of speakers are you making ?

Good luck.

DocP
--
 
pinkmouse said:
Can I clear up a little misconception here, if panels are cut true and square, very little pressure is needed to assemble joints.

Contrary to popular opinion,normal white or yellow wood glue does not have to be squeezed right out of the joint, in fact, this makes the joint weaker, as less glue remains to fix the parts together.

If the panels are well machined, then ordinary gaffer, (duct tape for our transatlantic cousins) will put enough pressure on a joint for a good result.

Now if your panels are out of true, that's when clamps or screws can be used, but with only enough pressure to bring the joint closed, not so tight all the glue is squeezed out.

I can be wrong, but MDF absorb wood glue so even if the joints are tight, they are very strong. I am using 4 big 36'' clamp to hold the box and I have good results.
 
DocP - Thanks for the advice.

I was talking to a mate who knows more than me about chamfering the edges this morning. He suggested the plane, sandpaper and sweat method too. I guess that's the route I'll probably take, but I'm going to concentrate on getting them to sound okay first - good point about diffraction off the sharp corners though.

I'll check out the builders merchant option on the MDF too - I'm hoping I'll be able to find somewhere which will cut the panels to reasonable accuracy too, although I might be being a bit optimistic.

The speakers I'm building first are just a simple small pair of vented boxes with Vifa drive units in them. I've pretty much finished the design with a 20 litre box going down to 45Hz which seems reasonable to do as a first attempt. I'm not attempting to do anything revolutionary - just build something half decent and give myself a chance to experiment and learn a little.

This is basically a bit of an experiment before I start a more ambitious project of making an active pair of studio monitors which will probably be sealed units with KEF drivers and active crossovers.
 
DocP said:
Hi Redeye,
You should also consider chamfering the edges of the front panel. It helps to minimise the edge diffraction effects and improves imaging. To do a professional job you really need a router for this but I have done a pretty decent job in the past with a hand plane, sandpaper and a lot of effort.
--

Something like this?:D

Chamfering refers to the mounting surface or the actual corners of the box?
 

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Redeye said:
I think I'll stick to the glue and screws approach to start with and put the aesthetics as a lower priority for now, although I take your point about it making it a lot harder to make them look good.

Going off on a slight tangent here, what finishing methods (painting etc.) work well on MDF? I've really not thought about this too much yet - I'm much more concerned with making them sound good, but I guess it's worth bearing in mind.

If i need a pretty cabinet, i get my buddy Chris to build them (i keep him well stocked with vintage drivers). I'm very use glue & screws assembly, then i will often put a layer of plastic laminate over the top. The laminate makes the box more presentable, but it also stiffens it up -- when i'm going all out on a box, i'll also laminate the inside. Half-inch ply with a layer of laminate both sides is a pretty good box-building material.

dave
 
edge round-overs

When doing round-overs on the cabinet edges, keep in mind that what is round is very dependent on the frequency in question. A 1/2" roundover does little more than add cosmetics and help avoid cuts and bruises from the sharp corners. To get really effective down into the upper midrange they need to be fairly large, 2, 3, even 4" radius. Baffle surface treatments and careful positioning of the drivers can make a big difference wrt edge diffraction issues.

dave
 
Re: edge round-overs

Hi electricashman,

Nice looking box. Reminds me of the Bose PA speakers that were everywhere about 10 years ago. You should get good dispersion from this but it's not what I had in mind. I was thinking of removing the sharp edges from the corners of the box.


planet10 said:
When doing round-overs on the cabinet edges, keep in mind that what is round is very dependent on the frequency in question. A 1/2" roundover does little more than add cosmetics and help avoid cuts and bruises from the sharp corners. To get really effective down into the upper midrange they need to be fairly large, 2, 3, even 4" radius. Baffle surface treatments and careful positioning of the drivers can make a big difference wrt edge diffraction issues.

dave

Yep. I'm with planet10 on this one. The larger the radius of curvature you can build into the corner the better, without going over to a cylindrical enclosure. There's a thread in this forum, probably in the loudspeaker section, by somebody who did a thesis on diffraction effects. The work was basically a rehash of work published in the 1950s that has been subsequently published in a couple of texts. I don't have them to hand right now so I can't say which off the top of my head.

Basically, to minimise the diffraction effects, put a large chamfer on the conrners of a rectangular box that has sides (l x w x h) that are not integer multiples of each other and then place the driver asymmetrically in the front of the box.

DocP
--

ps I like the site Planet10. I'm a big fan of TL's. Only speaker worth building IMO. I'm going to have a go at some drainpipes with full range drivers for a laugh, when I get time.....if that ever happens.
 
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