Metal Bracing in PE Sub Cabinet - diyAudio
Go Back   Home > Forums > Loudspeakers > Subwoofers

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 3rd October 2007, 04:52 AM   #1
diyAudio Member
 
Join Date: Jan 2003
Location: LA
Default Metal Bracing in PE Sub Cabinet

Hi all,
I have bought the Rythmik DS12 kit, and the Parts Express 2 Cu Ft subwoofer cabinet to put it in.

Based on some advice from Rythmik, I was going to add some 2x2's into it, for some additional bracing.

Then, on another forurm, someone suggested I use threaded rods for bracing. I could use the nuts to expand the rod, to press fit the rod into the cabinet.

I took this suggestion a little farther.

My current plans are to brace the front (speaker) wall with 1x1x1/8 steel angle bars. I cut four of them to size, and I have some aluminum blocks to join them angles at the corners. I will have tapped holes every few inches on the angles, to hold bolts to hold the angles to the wall. When I put them in, I will add some 2 ton expoxy, and then screw them in. I wasn't sure how much difference this would make, but I figured it couldn't hurt to stiffen the front wall as much as possible.

The cabinet has one wooden brace, running between the side walls. I was going to add 4 rod braces, two on the unbraced wall, one on the braced wall, and one from the front to back wall.

The braces will end into blocks of hard wood, about 1x4x4. There will be holes in the blocks for the rods to enter. These blocks will be glued to the walls, and I will torque down the nuts on the rods.

My aim is the torque the nuts enough to apply force to the walls, so it would slightly bow out the walls. I think that by stressing the walls like this, the walls will be stiffer then using a conventional brace.

These rods will be 1/2", because I already had one that size.

Any comments? Ways to improve?

At this point, I have one main concern. The angles are slightly magnetic, when I put two pieces close enough to each other, I feel a small force. Idealy, they would not be magnetic, but I don't think their small amount of magnetism will be enough to effect the driver.

Randy
__________________
My system is here
http://randytsuch-audio.blogspot.com/2005/10/my-system.html
  Reply With Quote
Old 4th October 2007, 05:20 PM   #2
badman is offline badman  United States
diyAudio Member
 
badman's Avatar
 
Join Date: Sep 2003
Location: Sunny Tustin, SoCal
Your idea works. Pre-tensioning is a scheme I've used in a variety of cabinets and does increase bracing efficacy.

The magnetism won't bother the driver.
__________________
I write for www.enjoythemusic.com in the DIY section. You may find yourself getting a preview of a project in-progress. Be warned!
  Reply With Quote
Old 5th October 2007, 03:19 PM   #3
diyAudio Member
 
Join Date: Jan 2003
Location: LA
Quote:
Originally posted by badman
Your idea works. Pre-tensioning is a scheme I've used in a variety of cabinets and does increase bracing efficacy.

The magnetism won't bother the driver.
Hi
Thanks for the reply.

I thought it was a good plan, but it is nice to get confirmation.

Just got home from a business trip, so I hope to get most of it done over the weekend.

Randy
__________________
My system is here
http://randytsuch-audio.blogspot.com/2005/10/my-system.html
  Reply With Quote
Old 5th October 2007, 03:57 PM   #4
GM is offline GM  United States
diyAudio Member
 
GM's Avatar
 
Join Date: Jun 2003
Location: Chamblee, Ga.
Greets!

Historically, the way to brace with threaded rod is to mount the driver with it so that the baffle and rear wall are coupled to the driver, so at least four is required for the front/rear and multiple ones should be used in a calculated, or at least random, pattern for the other two parallel walls. Doing it so that they can be tied together where they cross further helps to keep the cab from 'breathing'. Metal tubing is used between the locking nuts on long runs of smaller diameter threaded rod to stiffen/damp them, so where practical, large diameter all-thread rod as used on DIY component rack designs is preferred.

WRT joint bracing, just gluing in the angles are sufficient/superior since any through fasteners will weaken the joints.

Whether the panels are bowed out or in depends on the way the corner joints are overlapped. Regardless, over a relatively short time I've found wood products to take a set, so the benefit of pre-stressed is lost unless it warps in a complementary way, which shouldn't happen with the materials required for speaker building in general and subs in particular.

GM
__________________
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
  Reply With Quote
Old 5th October 2007, 07:37 PM   #5
diyAudio Member
 
Join Date: Jan 2003
Location: LA
Quote:
Originally posted by GM
Greets!

Historically, the way to brace with threaded rod is to mount the driver with it so that the baffle and rear wall are coupled to the driver, so at least four is required for the front/rear and multiple ones should be used in a calculated, or at least random, pattern for the other two parallel walls. Doing it so that they can be tied together where they cross further helps to keep the cab from 'breathing'. Metal tubing is used between the locking nuts on long runs of smaller diameter threaded rod to stiffen/damp them, so where practical, large diameter all-thread rod as used on DIY component rack designs is preferred.
I am trying to figure out how to mount the driver with a threaded rod.
Are you supposed to glue down the rod to the back wall? Then, I could run the rod through the baffle, then driver, and use a nut to hold the driver down. I guess that would work, and would couple the rear and front walls with the driver.
Oh, and as I think about it, I think I am lmiited in where I could add these rods, the plate amp hole has already been made, and it will interfere with some of these.

Quote:
Originally posted by GM

WRT joint bracing, just gluing in the angles are sufficient/superior since any through fasteners will weaken the joints.
Are you saying I should not use the screws to hold the angles down? One reason to use the screws was to act as a "clamp", to hold the angles while the epoxy dries. However, I could just use clamps in the middle, and screws on the ends. I could remove the end screws once the epoxy dries.
But, I am wondering why the screws would weaken the joints? I would think they would help make it stronger?

Quote:
Originally posted by GM

Whether the panels are bowed out or in depends on the way the corner joints are overlapped. Regardless, over a relatively short time I've found wood products to take a set, so the benefit of pre-stressed is lost unless it warps in a complementary way, which shouldn't happen with the materials required for speaker building in general and subs in particular.
GM
Corners are just glued together. Nothing fancy like dovetails. I am not sure if they used any rabbits, or if they just glued and clamped.

Thanks for the advice
Randy
__________________
My system is here
http://randytsuch-audio.blogspot.com/2005/10/my-system.html
  Reply With Quote
Old 5th October 2007, 09:52 PM   #6
GM is offline GM  United States
diyAudio Member
 
GM's Avatar
 
Join Date: Jun 2003
Location: Chamblee, Ga.
Default Re: Metal Bracing in PE Sub Cabinet

Greets!

You're welcome!

Hmm, that sucks! Oh well you can only do the best you can with what you have to work with.

Normally, the rod goes through the baffle, driver and back wall, though it could be anchored in a block, but then the only way to tension everything properly would be by using 'U' shaped shims AFAIK. Anyway, you tighten/tension the baffle to the rear wall by locking down the rod to the baffle on both sides, then tighten the locknut at the rear. Remove the hardware on the front side of the baffle and install the driver with them. Now the driver is connected to a very rigid column within a column. This is an especially useful way to mount bipole drivers

Glue two pieces of wood together and let it dry. Now bust it apart and what fails? Not the glue joint, but the material around it. What do you remove when you add a screw? The material, so now there's less material with a much poorer bonding thread/material junction which among other things reduces the glue's bonding integrity.

Is it a real world problem in a speaker cab, probably not unless it's in a prosound app that gets tossed around and/or 'flown', but it's more materials/labor that at best accomplishes nothing in the scheme of things, so I wouldn't use any screws unless the glue only works well if clamped and/or doesn't have enough stiction to hold it in place while curing, which I don't recommend using either. FWIW I recommend construction adhesive applied with a caulk gun, thick n' sticky and doesn't need clamping to work well. Great for gluing/sealing joints too. The downside is that it's not an easy clean-up and unless you can get an airtight seal on the cartridge you'll wind up throwing any left over away. Anyway, if you use screws I recommend just using as few short drywall or similar as practical from the inside, remove them once cured and fill the holes with more glue.

GM
__________________
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
  Reply With Quote
Old 6th October 2007, 03:45 PM   #7
diyAudio Member
 
Join Date: Jan 2003
Location: LA
Default Re: Re: Metal Bracing in PE Sub Cabinet

Quote:
Originally posted by GM
Greets!

You're welcome!

Hmm, that sucks! Oh well you can only do the best you can with what you have to work with.

Normally, the rod goes through the baffle, driver and back wall, though it could be anchored in a block, but then the only way to tension everything properly would be by using 'U' shaped shims AFAIK. Anyway, you tighten/tension the baffle to the rear wall by locking down the rod to the baffle on both sides, then tighten the locknut at the rear. Remove the hardware on the front side of the baffle and install the driver with them. Now the driver is connected to a very rigid column within a column. This is an especially useful way to mount bipole drivers

Glue two pieces of wood together and let it dry. Now bust it apart and what fails? Not the glue joint, but the material around it. What do you remove when you add a screw? The material, so now there's less material with a much poorer bonding thread/material junction which among other things reduces the glue's bonding integrity.

Is it a real world problem in a speaker cab, probably not unless it's in a prosound app that gets tossed around and/or 'flown', but it's more materials/labor that at best accomplishes nothing in the scheme of things, so I wouldn't use any screws unless the glue only works well if clamped and/or doesn't have enough stiction to hold it in place while curing, which I don't recommend using either. FWIW I recommend construction adhesive applied with a caulk gun, thick n' sticky and doesn't need clamping to work well. Great for gluing/sealing joints too. The downside is that it's not an easy clean-up and unless you can get an airtight seal on the cartridge you'll wind up throwing any left over away. Anyway, if you use screws I recommend just using as few short drywall or similar as practical from the inside, remove them once cured and fill the holes with more glue.

GM
Hi GM
I see your point about the screw, but the surface area of about seven #6 screws is pretty insignificant in a piece of metal 1 1/8 inches wide, by 15 inches long.

However, I was worried about air leaking around the screws, so with your encouragement, I am thinking about forgetting the screws.

For using threaded rods for mounting the speaker, I looked at that some more last night, when I got home and could look at my cabinet.

In one corner of the driver, I can't mount any rods, but I could still use up the 6 rods for mounting the driver. I bought a few 10-32 rods last night to do this. I will use some rods, and tnuts/screws everywhere else.

I was going to mount the rods to a piece of wood glued to the back. Figured I could make a flat hole with a forstner bit, that I could wedge a nut into. I could screw the rod in, then put another nut on the other side of the wood.

But, this would be a hassle to put together. I am thinking about just drilling some holes in the back wall. to run the rods through, and then just put a nut/washer on both sides of the wall.

I should have some time today to mess with this some more, and figure out how to do it.

Randy

I am still planning to use 2 ton epoxy, and will just clamp it down while it dries. I still want to clamp to get the angle close to the baffle because I think the angle will make the baffle more rigid the closer it is to the baffle.
__________________
My system is here
http://randytsuch-audio.blogspot.com/2005/10/my-system.html
  Reply With Quote
Old 9th October 2007, 12:35 AM   #8
diyAudio Member
 
Join Date: Jan 2003
Location: LA
OK, so I worked on it some over the weekend.
I ended up buying some 10-24 threaded rods, that is the biggest size that fits through the driver holes. Three of the holes will still use tnuts/screws, then I will use 10-24 rods for the other 5 holes.

Here is a pic of the sub front, with some of the threaded rods installed
Click the image to open in full size.


The boards in the bottom are not glued down yet. They have nuts on the other side, as shown in this pic. I will also install nuts on the top side, to hold the rod in place.
At the driver side of the rod, there will be a nut/washer on top of the driver,and another set under the baffle wall.
Click the image to open in full size.


I also glued down the angle irons, on the front baffle. A couple are glued down, and the other two are clamped, and drying.
Click the image to open in full size.

So, I need to glue down the boards holding the threaded rods, and then add the rods that will brace the side walls.

I am a little concerned that the 10-24 rods can bend, because they are only size 10, and it's about 15.5 inches across the sub. I was thinking about getting a larger diameter rod, I have some 7/16" rods, cutting them shorter than the 10-24 rods, then gluing them together. There would be a short length of 10-24 at each end which was not reinforced, but for most of the length, it would be much stronger. I don't think it would flex anymore, like it does now. I will probably try one out, to see how it works, then do a couple others if it works as planned.

BTW, I have more pics over here
http://www.audiocircle.com/gallery/t...php?album=1816

Randy
__________________
My system is here
http://randytsuch-audio.blogspot.com/2005/10/my-system.html
  Reply With Quote
Old 23rd October 2007, 12:47 AM   #9
diyAudio Member
 
Join Date: Jan 2003
Location: LA
Ok, I am now basically finished.

So, the rest of the story.

In the previous pics, there were the #10 rods that I installed for mounting the driver. #10 rods are not very big, especially across the 15.5 box width, so I decide reinforcement would be good, I added a 7/16" rod with gorilla glue, and tie wrapped them while the glue was drying. It is the vertical rod in this picture.
The horizontal rod is a 1/2" threaded rod that goes from side to side. All the rods that go to the side walls end into blocks that are around 4x4x1. I used nuts to push out against these blocks. The blocks were glued against the side walls, and I used some locking nuts, and thread lock, to keep the nuts from coming loose.
Click the image to open in full size.



Another pic of the inside.
I painted the inside, because I read about MDF breathing, and it is better to seal it with paint.
Click the image to open in full size.


I positioned the braces to try to make them intersect as much as possible. Then, I used gorilla glue to hold them together. Now, they are very stiff, you can push on them hard, and get almost no deflection. The #10 rods used to deflect easily, maybe 3/4" from side to side, before I reinforced them.
Click the image to open in full size.


One more, from the back. I added three rods on each side wall, and there are 5 rods going from front to rear, that also hold the driver down.
Click the image to open in full size.

I installed some spiked feet from PE, but I forgot to take pictures of them. Only problem here was when I drilled the front holes, I hit the L bracket I added to the front wall, so I had to move the feet back a little, and had to fill the holes with sealer.

Sub is put together now, sitting in my HT. I set it up this morning, and calibrated it, but I want to play with the settings after I let it break in a while.

Won't be able to comment on the sound for a week or two, after I put some time on it.

I do have a couple things left I would like to do. Rythmik suggested I put some 1-2" thick polyfill sheet on the walls. Said I could buy from auto upholstery place, but I found this stuff
http://www.mcminone.com/product.asp?...t%5Fid=LS00916

I was going to buy a couple packs, and put on the walls where I can.

I also want to add some sealer where the rods meet the rear of the front wall, to make sure I am getting a good seal here. I already put in sealant in the spike holes, and in the driver holes where I am using a tnut/screw. Want to make sure there are no air leaks anywhere.

Thanks for the advice.

Randy
__________________
My system is here
http://randytsuch-audio.blogspot.com/2005/10/my-system.html
  Reply With Quote
Old 24th October 2007, 04:02 AM   #10
GM is offline GM  United States
diyAudio Member
 
GM's Avatar
 
Join Date: Jun 2003
Location: Chamblee, Ga.
Greets!

You're welcome! Looks impressive, though I had to use the link in a previous post to the rod system. I assume you're seeing the same AudioCircle banners as I am in your posts. Yeah, even minor leaks in a sub can really alter its alignment.

GM
__________________
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Cabinet bracing for Rabbitz Vifa P13 / D27 speaker gaust Multi-Way 1 11th June 2009 02:31 PM
Bracing the cabinet Lewis Moon Multi-Way 5 4th October 2008 11:54 PM
Cabinet Bracing (Tie Sides to Frt & Rear?) Ric Seyler Multi-Way 8 22nd January 2008 07:58 PM
metal grill material for amp cabinet timsch75 Instruments and Amps 7 22nd July 2006 12:05 AM
When does cabinet bracing become necessary? mazeroth Multi-Way 9 4th December 2004 03:43 PM


New To Site? Need Help?

All times are GMT. The time now is 02:39 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2