# Subwoofer box and lots of 5/16 hardwood dowels.



## Johanx3 (Dec 11, 2015)

Hi, What do you think about this? I made a speaker box using 3/4 MDF. It has bracing and the panels are about 19"x15". its a big box that holds a 15" subwoofer driver.

Want to joint every edge by using 5/16 hardwood dowels. which would requiere about 80 5/16 dowels (1.5" long). Its ridiculous putting a dowel every 1.5" ? or is it just okay because the enclosure is big and the subwoofer is very powerful, "about 1000watts". Need to use dowels because don't trust using screws on MDF, if my box was made of plywood, then I could simply use screws, but need to use 5/16 dowels. Or should I even use more quantity?


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## Steve Neul (Sep 2, 2011)

Using dowels ever 1 1/2" is overkill. If you glue the joint together a dowel ever foot is more than sufficient.


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## GeorgeC (Jul 30, 2008)

A thousand watts? Where will this speaker be used? In the super dome?

George


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## Johanx3 (Dec 11, 2015)

Steve Neul said:


> Using dowels ever 1 1/2" is overkill. If you glue the joint together a dowel ever foot is more than sufficient.


I can't imagine the walls being joined just by a 5/16 dowel every 1 foot, I mean, I was expecting at the very list 1 dowel every 3 inches. I want guaranties that the box won't take apart no matter what (regular but heavy use), so for that reason I saw a big number of dowels. remember that 5/16 is not too thick, just perfect for 3/4 mdf I thought. I am still doubting, please more opinions about this, although I am expecting going with once every 2", yeah, too much drilling, and glue and dowels, but that will guarantee a "perfect join". 



GeorgeC said:


> A thousand watts? Where will this speaker be used? In the super dome?
> 
> George


It's primordially for car audio, for cars like vans. Surprise to hear that there are subwoofers around 2K watts.


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## shoot summ (Feb 21, 2014)

No need for dowels, screws placed at the same interval will be stronger. For a box that size bracing is more crucial than doweling the joints.

Many audio people talk in max terms, 1000 watts sounds like a max number, what are you driving the sub with amp wise? Is this a sealed box or ported?

Did I mention you don't need dowels?


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## hwebb99 (Nov 27, 2012)

I have built speaker boxes before and screws work fine.


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## bmarshall9686 (Jan 17, 2016)

1000 watts really isn't that much for a subwoofer, however it is still plenty to rattle a car. So I have 2 suggestions. 

1. Get rubber washers for your license plate. 

2. If you are really worried use finger joints. 

I would strongly recommend making a ported box, with a folded driver, angled inside. For subs to be effective they need space. It's takes around 22 feet to create a full sound wave at 80hz.

Not that you can't just do what ask the car audio people do, its loud, it works, just my thoughts. My day job is in live production so I am a little biased.


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## Tree Hugger (Sep 1, 2011)

Glue and screws is all that is needed.( I've built them and have seen then built ) and the screws are just to hold it together while the glue dries.
Corner block it if your concerned.


bmarshall is right
" For subs to be effective they need space "


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## Steve Neul (Sep 2, 2011)

Johanx3 said:


> I can't imagine the walls being joined just by a 5/16 dowel every 1 foot, I mean, I was expecting at the very list 1 dowel every 3 inches. I want guaranties that the box won't take apart no matter what (regular but heavy use), so for that reason I saw a big number of dowels. remember that 5/16 is not too thick, just perfect for 3/4 mdf I thought. I am still doubting, please more opinions about this, although I am expecting going with once every 2", yeah, too much drilling, and glue and dowels, but that will guarantee a "perfect join".
> 
> 
> 
> It's primordially for car audio, for cars like vans. Surprise to hear that there are subwoofers around 2K watts.


Keep in mind that MDF is just a sheet of paper, the same kind of paper that grocery sacks are made of. How well do you think glue would adhere to paper? I think you would run into monumental problems trying to drill dowels 1 1/2" apart. The more dowels you put in a joint the more chances you will have getting one a little off. Putting dowels 1 1/2" apart you are asking for a bunch of dowels to be a little off. Then when you go assemble it the dowels will prevent the parts from going together. A better method for what you are doing would be to put a spline in the joint. This would give you 100% coverage instead of every 1 1/2". I also agree with these guys you could glue and either nails or use screws to assemble the box.


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## Marv (Nov 30, 2008)

My side business is building subwoofer enclosures and as mentioned glue with screws in the appropriate sized pilot holes works fine (if you use nails be sure to clamp it as nails will not pull MDF tight enough to create a solid glue joint).

http://s29.photobucket.com/user/MrMarv/library/?sort=3&page=1

Built this one for my El Camino and powered it with a true 1000 watts rms


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## Rebelwork (Jan 15, 2012)

I don't think I'd use mdf...


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## Johanx3 (Dec 11, 2015)

Steve Neul said:


> Keep in mind that MDF is just a sheet of paper, the same kind of paper that grocery sacks are made of. How well do you think glue would adhere to paper? I think you would run into monumental problems trying to drill dowels 1 1/2" apart. The more dowels you put in a joint the more chances you will have getting one a little off. Putting dowels 1 1/2" apart you are asking for a bunch of dowels to be a little off. Then when you go assemble it the dowels will prevent the parts from going together. A better method for what you are doing would be to put a spline in the joint. This would give you 100% coverage instead of every 1 1/2". I also agree with these guys you could glue and either nails or use screws to assemble the box.


well, I cannot do the spline because the walls are now glued, just waiting for dowels or screws, anyway I had no tool for doing that, so this time my option is doweling or screwing. I found that 3/4 MDF is pretty strong and most speakers and subwoofers are built with it, problem is that it can easily split at the edges if you dont use the proper screws, to avoid disasters like mdf splitting, will simply use dowels, making straight holes is not a problem because I am going to use a drill bit guide. I think I will put a dowel every 2 inches.



Marv said:


> My side business is building subwoofer enclosures and as mentioned glue with screws in the appropriate sized pilot holes works fine (if you use nails be sure to clamp it as nails will not pull MDF tight enough to create a solid glue joint).
> 
> http://s29.photobucket.com/user/MrMarv/library/?sort=3&page=1
> 
> Built this one for my El Camino and powered it with a true 1000 watts rms


Wow thats very nice. :surprise2:



Rebelwork said:


> I don't think I'd use mdf...


Most subwoofers are made of MDF, because the high quality sound you get with it, only critic thing about using MDF, if the care of screwing the edges, something you can solve with dowels or box joints, I mean, its a very interesting material, cheap and very strong.


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## shoot summ (Feb 21, 2014)

Johanx3 said:


> well, I cannot do the spline because the walls are now glued, just waiting for dowels or screws, anyway I had no tool for doing that, so this time my option is doweling or screwing. I found that 3/4 MDF is pretty strong and most speakers and subwoofers are built with it, problem is that it can easily split at the edges if you dont use the proper screws, to avoid disasters like mdf splitting, will simply use dowels, making straight holes is not a problem because I am going to use a drill bit guide. I think I will put a dowel every 2 inches.
> 
> 
> 
> ...


So what do you expect the dowels to do in this instance? They have no compressive strength that will hold the box together like screws. They only have sheer strength the way you are installing them, and by removing 5/16 out of the MDF you are weakening it. As others have stated, the proper screws, installed properly, will be the best solution.

But it's your box, and it seems as though you have convinced yourself to use dowels, so I'm not really sure why you asked for advice?


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## Johanx3 (Dec 11, 2015)

shoot summ said:


> So what do you expect the dowels to do in this instance? They have no compressive strength that will hold the box together like screws. They only have sheer strength the way you are installing them, and by removing 5/16 out of the MDF you are weakening it. As others have stated, the proper screws, installed properly, will be the best solution.
> 
> But it's your box, and it seems as though you have convinced yourself to use dowels, so I'm not really sure why you asked for advice?


There's no way I will use screws on the edge of a MDF board, I have made several tests, and found that it splits very easily, however I found that machine screws work better if you clamp the board while screwing the screw, but although it did not split it, I won't trust it won't eventually split it with a hard movement. 

Take a look at this picture a took some minutes ago.

A - I screwed a #12 1.5" machine screw to a glued sandwich, it did not split although the screw went in so tight, not only because I pre drilled, but because it's very hard to split MDF on its face. To mention that I was near to the edge, but as I ran perpendicular to the fibers, nothing bad happened. 

B - I attacked the edge with same screw used on A, I properly pre drilled and clamp the area with a clamp and two wood pieces, once I removed the clamp, it did not split, but just as I said before, I won't trust a screw inserted in that side.

C - Here I used a coarse wood screw, which even had a self drilling in the tip, anyway I pre drill with my drill before screwing. It split and ruined the mdf very easi and horrible, maybe because of that head type, that make even easier splitting. 

D - Same test as C, just clampling the area with 2 more boards and C clamp, the damage was minor, but it split the edge.










You see guys? I think that you can use screws on mdf, but not in a edge. Dowel with get its compression once the glue expands and dries.


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## Marv (Nov 30, 2008)

I use screws in the edge of MDF all day long with no problems. In this picture I put a screw only a half-inch from the edge, another one three quarters of an inch away and another one 2 inches away with no splitting.


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## Johanx3 (Dec 11, 2015)

Marv said:


> I use screws in the edge of MDF all day long with no problems. In this picture I put a screw only a half-inch from the edge, another one three quarters of an inch away and another one 2 inches away with no splitting.


I think that the problem comes once you tight the screw to recommended torque. I have to say that I made a mistake in my test, specially with that wood screw, that head makes disaster if touches directly the edge, in real application that head should be placed in the face of the mdf board, so maybe I wont have that problem screwing my speaker box, but because I don't want to risk my two big boxes, was planning using the screws as if it were dowels, I mean, if they are 6mm counting the threads, my pilot hole its going to be 6mm, that way it can be inserted without stressing the mdf fibers, but what about the fixation? I will put wood glue in the hole and on screw, and that with make the magic. I did this before, what do you think? I am using a woodglue which is harder than wood.


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## Steve Neul (Sep 2, 2011)

If you drill a pilot hole for the screws and countersink it, screws shouldn't split the edge of MDF.


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## Rebelwork (Jan 15, 2012)

Johanx3 said:


> well, I cannot do the spline because the walls are now glued, just waiting for dowels or screws, anyway I had no tool for doing that, so this time my option is doweling or screwing. I found that 3/4 MDF is pretty strong and most speakers and subwoofers are built with it, problem is that it can easily split at the edges if you dont use the proper screws, to avoid disasters like mdf splitting, will simply use dowels, making straight holes is not a problem because I am going to use a drill bit guide. I think I will put a dowel every 2 inches.
> 
> 
> 
> ...


You sure? My four MTX AAL212's all made from Pb running on an old Pioneer with 125 wpc. I mean I turn off the BOSE when its time to run mice off and dust the rec room walls son>. My daughters MTX sub in her car is pb from the manufacturer.

When I was asked in the early 80's to make subs for a local audio deal I declined because they required pb and I thought it was a waste of time. Little did I know subs were the future:crying2::crying2:


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## Johanx3 (Dec 11, 2015)

Steve Neul said:


> If you drill a pilot hole for the screws and countersink it, screws shouldn't split the edge of MDF.


I countersink it, and anyway happened, as I mentioned it, what I did not do, was to make the countersink in the board which fibers are not running parallel (I mean, in the corner of a box attacking 2 pieces), but I don't know, I made a test with a machine screw and a big washer, thinking that if all head pressure falls on the washer and therefore cover more mdf area, it won't split, but it did it. Is it ok using #10 screw on 3/4 MDF? or should I use #8? I think for this time only going to dowel the screws with glue and drilling a same diameter hole. Next time will think in using plywood or even particulate board, which dont have this problem. I decided to use MDF, because had planned using some 2x2 timbers at every corner, that way I was supposed not to screw on any MDF edge, but plans changed and needed to get rid of the 2x2 timbers and now need to do what I said.


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## shoot summ (Feb 21, 2014)

Johanx3 said:


> I countersink it, and anyway happened, as I mentioned it, what I did not do, was to make the countersink in the board which fibers are not running parallel (I mean, in the corner of a box attacking 2 pieces), but I don't know, I made a test with a machine screw and a big washer, thinking that if all head pressure falls on the washer and therefore cover more mdf area, it won't split, but it did it. Is it ok using #10 screw on 3/4 MDF? or should I use #8? I think for this time only going to dowel the screws with glue and drilling a same diameter hole. Next time will think in using plywood or even particulate board, which dont have this problem. I decided to use MDF, because had planned using some 2x2 timbers at every corner, that way I was supposed not to screw on any MDF edge, but plans changed and needed to get rid of the 2x2 timbers and now need to do what I said.


Again, as others have clearly stated, no issues with the correct screws, properly installed screws, your test is flawed. 

Regardless, I think you should do what you want to do, as we wont convince you otherwise. There are DECADES of experience on the forum, that have all indicated screws will work. Your inexperience is making you think they wont. So this will be like raising kids, you have to let them take their own path sometimes, and find out if something works, or doesn't. It's just odd you ask for advice, and then wont take it.

And, you might do some research on the type of screws to use with MDF, I think you will find some interesting info...


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## Steve Neul (Sep 2, 2011)

Johanx3 said:


> I countersink it, and anyway happened, as I mentioned it, what I did not do, was to make the countersink in the board which fibers are not running parallel (I mean, in the corner of a box attacking 2 pieces), but I don't know, I made a test with a machine screw and a big washer, thinking that if all head pressure falls on the washer and therefore cover more mdf area, it won't split, but it did it. Is it ok using #10 screw on 3/4 MDF? or should I use #8? I think for this time only going to dowel the screws with glue and drilling a same diameter hole. Next time will think in using plywood or even particulate board, which dont have this problem. I decided to use MDF, because had planned using some 2x2 timbers at every corner, that way I was supposed not to screw on any MDF edge, but plans changed and needed to get rid of the 2x2 timbers and now need to do what I said.


I'm confused now. I thought your project entailed putting a screw into the edge of MDF. What you have illustrated I would use #10 screws and drill a 3/16" shank hole with a countersink through the MDF. The screws would pull down into the 2x2 timber just fine.


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## shoot summ (Feb 21, 2014)

Steve Neul said:


> I'm confused now. I thought your project entailed putting a screw into the edge of MDF. What you have illustrated I would use #10 screws and drill a 3/16" shank hole with a countersink through the MDF. The screws would pull down into the 2x2 timber just fine.


He's not going to use the timber...


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## Johanx3 (Dec 11, 2015)

shoot summ said:


> He's not going to use the timber...


I think you both are right men, and you shoot, I understand your point, I have seen how complex are those screws designed for MDF, I have never seen something like that before, but my point is still there, that although that screw go in correctly without splitting anything, I can't trust that in the future it won't rip... It was not a waste of time for anybody here, I was planning using the 5/16 hardwood dowels, but then I got what you said, that they will weak the board because they mass portion they are going to take, so no doubt that I am not going to use the 5/16 dowels, what I am going to do is pre drill with the same screw thread diameter, and put in some glue in both places, hole and screw, that way the MDf hole will be reinforce with the glue, which is stronger than MDF, guarantying that screw won't cause a future split. It's a little annoying doing this, but will do it just in this project. These woodglues, tends to expand, so there is where I will get the strength, have you seen how hard wood glue is? it dries like rock!. I am going to put one every 3 inches.


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## Tree Hugger (Sep 1, 2011)

Drywall screws will work also, but experiment with them on some scrap to get the correct pilot hole ( they can snap under to much torque.


*In MDF, screws are used as clamps while the glue dries..they serve no other purpose.*


You could remove the screws afterwards and lose no strength , *the strength is in the glue joint.*


You stated that you have already glued it ...if its holding ok adding screws or dowels would be pointless.


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## Johanx3 (Dec 11, 2015)

Tree Hugger said:


> Drywall screws will work also, but experiment with them on some scrap to get the correct pilot hole ( they can snap under to much torque.
> 
> 
> *In MDF, screws are used as clamps while the glue dries..they serve no other purpose.*
> ...


Of course you lose strength if only glued, because with screws, the masses are connected internally, so the surfaces wont peal off at a heavy use, because this is a powerful subwoofer, not for 8" driver but for 15". Its like gluing a washer in a surface, if you add a screw, then it's harder to remove it. Next time I am going to do 1 inch box joints, that's the strongest way to join mdf and theres no need for screws.

I thought a new method to join mdf, it uses lots of glue, what if you fill the pilot holes with glue instead of screwing them? once glue dries, it turns into rock, you may fill pilot hole several times until glue stabilizes and cover the area, however, I am still with the idea of using #10 screws as dowels.

Will try to make the test of the 6mm pilot holes filled with glue. Titebond dries as rock, I dont know if any other glues are the same hard. Have tried elmers as well, incredible woodglue as well. I may say that this is a better task for epoxy, but this one is expensive in big quantity, and I observed how woodglue has nothing to envy to epoxy, at least in wood usage.


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## Johanx3 (Dec 11, 2015)

So what do you think about my method? Here I am going to explain why it has huge potential. In the picture below, theres a MDf board edge, with a hole. Green dot is the screw, red section is the glue. Once the glue is dried, we will find that all the fibers around the screw, have been merged and reinforced, so it won't split even with hard movement of the screw. Few hours ago I read a comment of a person, who usually uses crazy glue in the pivot hole, he got the same idea and saw how convenient is gluing those fibers, I would prefer wood glue instead.


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## notskot (Feb 22, 2015)

3/4" is thinner than I'd like, and the overall volume seems very small for that much woofer. I'd be inclined to use at least 1" material with screws and glue, but would put a wood brace in each corner for the screws to grab into.


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## woodnthings (Jan 24, 2009)

*This is a bit too technical ...*

Is a glue joint strong? Yes, if properly made and clamped, it's stronger than the surrounding wood. Is MDF wood? ...kinda, sorta. If you edge glue MDF to itself will it break at the glue joint IF Twisted ... if pressed down in the joint? If you joint MDF at right angles, how strong is it? If you use screws, is it any stronger? How strong is a glued MDF joint.

Then the quest5ion becomes "Do you need screws in a right angle glued MDF joint?" 

Then another question is "In a dynamic loading, like sound waves, what is the effect on glued joints?" AND should they be "flexible" rather than rock hard solid. Maybe PVC glue, having some softness/flexibilty is best? I also wonder about Liquid Nail Construction adhesives...?


Sorry for all the questions, but that's what I'd like to know. Some testing would be required. :surprise2:


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## Johanx3 (Dec 11, 2015)

notskot said:


> 3/4" is thinner than I'd like, and the overall volume seems very small for that much woofer. I'd be inclined to use at least 1" material with screws and glue, but would put a wood brace in each corner for the screws to grab into.


Actually yesterday decided to use the 2x2 timbers as corners I discarded before, they represent about 0.2 3F, but I see its a bad necessary, just for the weight and mass they take, what I don't know if 2.1 CF is still good for 15" driver, most manufactures ask for 2 CF for their 15" drivers, but have seen larger 15" boxes.

Total space was 2.3 3F, but I also have a 2x4 cross that links the 5 walls, this cross also connects with some external panels I have in the center of 4 main walls, I thought in this concept some days ago, since the center of the walls is the most flexible part of a speaker box. It will be a heavy box, but with premium sound though. 

concept of bracing is something like this picture I made, I also made some external work as a superior belt that reinforces the upper side, just around the driver, double baffle and a cover, so this thing will be a war tank once done. So now with the 2x2 battens there, can link every mdf face without screwing on their edge, but just in their faces.


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