Is this enough bracing - AVS Forum | Home Theater Discussions And Reviews
Forum Jump: 
 
Thread Tools
post #1 of 11 Old 09-20-2017, 07:53 AM - Thread Starter
AVS Forum Special Member
 
tjcinnamon's Avatar
 
Join Date: Jul 2008
Posts: 2,959
Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quoted: 1811 Post(s)
Liked: 490
Is this enough bracing

I have a 17x11.5 ID box so it's a small box and I don't want to load it with too much bracing. I have a CNC machine so I have 1/8" dado grooves on all sides of the bracing. The bracing touches all 4 sides of the box for gluing.

The bracing is basically every 1/3" of the length of the box (@6" in and 11" in). It's half inch MDF.

Thoughts?

Attached Thumbnails
Click image for larger version

Name:	bracing.png
Views:	578
Size:	13.8 KB
ID:	2285364  

NAD 758 v3 with Dirac 7.4.4 + Rotel 976 + Panamax M5300-PM
Paradigm Prestige 75F's + 55C; 8x Paradigm CI Pro P65-R's
DIY MBMs: VRK Build thread + 2x Rotel 981 (bridged)
Sub: 2x Rythmik LVX12 + MiniDSP
DIY Room Treatments: Dutch Floral Prints
tjcinnamon is offline  
Sponsored Links
Advertisement
 
post #2 of 11 Old 09-20-2017, 11:32 AM
AVS Forum Special Member
 
asarose247's Avatar
 
Join Date: Mar 2010
Location: DIY enabled in SoCal / OC
Posts: 4,427
Mentioned: 105 Post(s)
Tagged: 2 Thread(s)
Quoted: 1246 Post(s)
Liked: 1090
The box corners, where edges meet are already strong . .

it;s the interior areas of the panels that need stabilizing . . made inert

you're right about using the the 1/3rd idea . .

depending on the box, that can be usually around 6" to 8" spacing

you can google bracing at the site, there's a good pic using doweling that looks good for your box

for a box that small some may suggest 1/2" in a criss-cross lattice

DIY FAN Denon X4400 , ATI A 2000 for 7.4.6 SCATMOS Sammy 82" 4K/HDR
L/R: Fusion 15 V2 , C: 88 Special , SL/SR: 88 Special(V2) , RL/RR: F-3, TF/TR: Volt 6's TM: SLX, FH: F4Q4
SUBMAXIMUS V2, ,Submaximus V3,LOWARHORNCustom Dual Driver VBSS,2 x 6000DSP
asarose247 is offline  
post #3 of 11 Old 09-20-2017, 12:06 PM
AVS Forum Special Member
 
asarose247's Avatar
 
Join Date: Mar 2010
Location: DIY enabled in SoCal / OC
Posts: 4,427
Mentioned: 105 Post(s)
Tagged: 2 Thread(s)
Quoted: 1246 Post(s)
Liked: 1090
that's just 1 idea
Attached Images
File Type: jpg bracing_zpsas9pf042.jpg (157.8 KB, 130 views)

DIY FAN Denon X4400 , ATI A 2000 for 7.4.6 SCATMOS Sammy 82" 4K/HDR
L/R: Fusion 15 V2 , C: 88 Special , SL/SR: 88 Special(V2) , RL/RR: F-3, TF/TR: Volt 6's TM: SLX, FH: F4Q4
SUBMAXIMUS V2, ,Submaximus V3,LOWARHORNCustom Dual Driver VBSS,2 x 6000DSP
asarose247 is offline  
Sponsored Links
Advertisement
 
post #4 of 11 Old 09-20-2017, 01:14 PM - Thread Starter
AVS Forum Special Member
 
tjcinnamon's Avatar
 
Join Date: Jul 2008
Posts: 2,959
Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quoted: 1811 Post(s)
Liked: 490
Quote:
Originally Posted by asarose247 View Post
that's just 1 idea
Whoa! Thats interesting. I'll look into it.

My primary concern was that I have the bracing only going one direction. But my think was that perhaps because the box was small and all 4 sides will be braced that it could be enough.

I have dado grooves for the bracing and rabbet joints all around the outside of every side.

NAD 758 v3 with Dirac 7.4.4 + Rotel 976 + Panamax M5300-PM
Paradigm Prestige 75F's + 55C; 8x Paradigm CI Pro P65-R's
DIY MBMs: VRK Build thread + 2x Rotel 981 (bridged)
Sub: 2x Rythmik LVX12 + MiniDSP
DIY Room Treatments: Dutch Floral Prints
tjcinnamon is offline  
post #5 of 11 Old 09-20-2017, 06:18 PM
AVS Forum Special Member
 
Vince_B's Avatar
 
Join Date: Aug 2001
Location: Hummelstown PA USA
Posts: 1,444
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 316 Post(s)
Liked: 212
When you assemble knock on the sides and just add some braces as needed. Dado nice but a snug fit and apply glue to both surfaces is fine too. Agree with the 6-8" above, if you do that you will be good. If the baffle is wider than driver by more than a few inches double it or brace front to back. Look at the Stonehenge design that is very smart bracing.

Sent from my SM-N910V using Tapatalk
Vince_B is offline  
post #6 of 11 Old 09-27-2017, 12:45 PM
AVS Forum Special Member
 
Join Date: Mar 2015
Location: Norway
Posts: 1,181
Mentioned: 16 Post(s)
Tagged: 0 Thread(s)
Quoted: 676 Post(s)
Liked: 138
This is a way more efficient bracing scheme if you are concerned about internal volume being lost.

Just make 2" by 1" lengths of mdf (but preferably something stiffer so you can get away with thinner bracing, like normal wood planks or flooring particle-boards) and apply them this way. This uses half the amount of material as a window bracing scheme, and provides 95% of the strength of bracing from opposite face to opposite face (proven by autodesk fusion 360 simulations). So you can use more braces without losing lots of internal volume. The basic rule of thumb is that the distance to the nearest brace is the biggest weak-point, not the thickness or stiffness of the braces themselves. Bracing four points on a square 12 by 12 surface so that there is only 4 inches between each brace (not counting diagonally), is far worse than bracing 9 points, even if the 9 braces are much weaker. If you have a large enclosure you can just make a combo of diagonal and cross-bracing, like this:

You'll get away with using the scraps from making the enclosure, usually. instead of cutting holes in perfectly good large sheets of mdf or plywood or particleboard.

PS: The bracing scheme is WITH the external panels, you don't make bracing in this shape and then add that to the enclosure faces themselves. So basically this is the effective bracing material used:

PPS: The distance between every point where the bracing meets the panels, is the same. Even if the drawing is not to scale perfectly.
PPPS: Just remember you should treat (its called "doping") the inner surface of your mdf, with lets say epoxy or polyester. Just a dab with a brush to paint on a decent covering layer about 1" larger than the bracing, wherever you plan to put bracing (but then against just use a roller and apply it everywhere inside, polyester is dirt cheap). Simulations show that mdf is just waaaay too flexible for bracing to be really effective with smaller than 2" diameter footprint of contact, its like bracing your thumb against a needle, where the needle is the bracing and the thumb is the mdf.

Last edited by ronny31; 09-27-2017 at 12:54 PM.
ronny31 is offline  
post #7 of 11 Old 09-27-2017, 03:14 PM - Thread Starter
AVS Forum Special Member
 
tjcinnamon's Avatar
 
Join Date: Jul 2008
Posts: 2,959
Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quoted: 1811 Post(s)
Liked: 490
Quote:
Originally Posted by ronny31 View Post
This is a way more efficient bracing scheme if you are concerned about internal volume being lost.

Just make 2" by 1" lengths of mdf (but preferably something stiffer so you can get away with thinner bracing, like normal wood planks or flooring particle-boards) and apply them this way. This uses half the amount of material as a window bracing scheme, and provides 95% of the strength of bracing from opposite face to opposite face (proven by autodesk fusion 360 simulations). So you can use more braces without losing lots of internal volume. The basic rule of thumb is that the distance to the nearest brace is the biggest weak-point, not the thickness or stiffness of the braces themselves. Bracing four points on a square 12 by 12 surface so that there is only 4 inches between each brace (not counting diagonally), is far worse than bracing 9 points, even if the 9 braces are much weaker. If you have a large enclosure you can just make a combo of diagonal and cross-bracing, like this:

You'll get away with using the scraps from making the enclosure, usually. instead of cutting holes in perfectly good large sheets of mdf or plywood or particleboard.

PS: The bracing scheme is WITH the external panels, you don't make bracing in this shape and then add that to the enclosure faces themselves. So basically this is the effective bracing material used:

PPS: The distance between every point where the bracing meets the panels, is the same. Even if the drawing is not to scale perfectly.
PPPS: Just remember you should treat (its called "doping") the inner surface of your mdf, with lets say epoxy or polyester. Just a dab with a brush to paint on a decent covering layer about 1" larger than the bracing, wherever you plan to put bracing (but then against just use a roller and apply it everywhere inside, polyester is dirt cheap). Simulations show that mdf is just waaaay too flexible for bracing to be really effective with smaller than 2" diameter footprint of contact, its like bracing your thumb against a needle, where the needle is the bracing and the thumb is the mdf.
Thanks for the great detail! I have come close to finishing my designs for a CNC machine. I'll redo how I have the bracing to meet your specs. Its just as easy. I just need to draw it out and the machine will cut it.

I could use Baltic Birch for the bracing. That's much more rigid.

NAD 758 v3 with Dirac 7.4.4 + Rotel 976 + Panamax M5300-PM
Paradigm Prestige 75F's + 55C; 8x Paradigm CI Pro P65-R's
DIY MBMs: VRK Build thread + 2x Rotel 981 (bridged)
Sub: 2x Rythmik LVX12 + MiniDSP
DIY Room Treatments: Dutch Floral Prints
tjcinnamon is offline  
post #8 of 11 Old 09-28-2017, 12:02 AM
AVS Forum Special Member
 
Join Date: Mar 2015
Location: Norway
Posts: 1,181
Mentioned: 16 Post(s)
Tagged: 0 Thread(s)
Quoted: 676 Post(s)
Liked: 138
The whole point of this bracing scheme is that you can make due with just scraps from your project, since you can build the bracing from straight thin pieces that you cut 45 degree at the ends. Please don't harvest a whole sheet just for bracing :P Just ask them to CNC the enclosure without the bracing, then you do the bracing yourself with a hand saw and some 1by1" or 1.5x1.5" wood pieces.

PS: If you're ever building LCR speakers this bracing makes them pretty much the lowest distortion speakers on the market. -30db or 1/1000th of the speaker output, will be noise from the enclosure panels moving. Unless you consider a 10 grand enclosure made from 4" thick braced glulam in your market bracket.

Last edited by ronny31; 09-28-2017 at 12:09 AM.
ronny31 is offline  
post #9 of 11 Old 09-28-2017, 09:29 AM
AVS Forum Special Member
 
Gouie's Avatar
 
Join Date: Jan 2006
Location: Edmonton, Alberta, Canada
Posts: 1,150
Mentioned: 7 Post(s)
Tagged: 0 Thread(s)
Quoted: 403 Post(s)
Liked: 278
Quote:
Originally Posted by ronny31 View Post
This is a way more efficient bracing scheme if you are concerned about internal volume being lost.

Just make 2" by 1" lengths of mdf (but preferably something stiffer so you can get away with thinner bracing, like normal wood planks or flooring particle-boards) and apply them this way. This uses half the amount of material as a window bracing scheme, and provides 95% of the strength of bracing from opposite face to opposite face (proven by autodesk fusion 360 simulations). So you can use more braces without losing lots of internal volume. The basic rule of thumb is that the distance to the nearest brace is the biggest weak-point, not the thickness or stiffness of the braces themselves. Bracing four points on a square 12 by 12 surface so that there is only 4 inches between each brace (not counting diagonally), is far worse than bracing 9 points, even if the 9 braces are much weaker. If you have a large enclosure you can just make a combo of diagonal and cross-bracing, like this:

You'll get away with using the scraps from making the enclosure, usually. instead of cutting holes in perfectly good large sheets of mdf or plywood or particleboard.

PS: The bracing scheme is WITH the external panels, you don't make bracing in this shape and then add that to the enclosure faces themselves. So basically this is the effective bracing material used:

PPS: The distance between every point where the bracing meets the panels, is the same. Even if the drawing is not to scale perfectly.
PPPS: Just remember you should treat (its called "doping") the inner surface of your mdf, with lets say epoxy or polyester. Just a dab with a brush to paint on a decent covering layer about 1" larger than the bracing, wherever you plan to put bracing (but then against just use a roller and apply it everywhere inside, polyester is dirt cheap). Simulations show that mdf is just waaaay too flexible for bracing to be really effective with smaller than 2" diameter footprint of contact, its like bracing your thumb against a needle, where the needle is the bracing and the thumb is the mdf.
Very interesting concept. Is there a recommended distance between the pieces of bracing (in your diagram, left hand side, distance from braces where they meet the side panel)? What about the recommended distance between full brace panels themselves - for example, on a larger 4 ft long box, how many brace panels would be required?
Gouie is offline  
post #10 of 11 Old 09-29-2017, 09:19 PM
AVS Forum Addicted Member
 
BassThatHz's Avatar
 
Join Date: Apr 2008
Location: Northern Okan range (NW Cascades region)
Posts: 10,815
Mentioned: 235 Post(s)
Tagged: 0 Thread(s)
Quoted: 3777 Post(s)
Liked: 4297
Matrix bracing is best:

Ideally: every 6 inches. 12inches at most.

Re-enforcing edges and corners is not needed as they are already strong, it is the flat areas in between that are weak and requires the most support.

Keep in mind that even one brace in the middle of each panel basically doubles the apparent thickness of the walls.
Adding 4 to each side nearly doubles it again, or every 6inches for large boxes.

Arguably: the "disdyakis triacontahedron" is one of the strongest 3D shapes. (say that 3 times fast)


Honeycomb pattern made out of carbon fiber would also be very strong.

This video at 10:40 shows a simple way to add strength to a surface (ribbing made of CF and foam.)
Attached Thumbnails
Click image for larger version

Name:	600cell.png
Views:	238
Size:	577.7 KB
ID:	2290636  
BassThatHz is offline  
post #11 of 11 Old 11-19-2018, 12:34 AM
AVS Forum Special Member
 
Join Date: Mar 2015
Location: Norway
Posts: 1,181
Mentioned: 16 Post(s)
Tagged: 0 Thread(s)
Quoted: 676 Post(s)
Liked: 138
Quote:
Originally Posted by Gouie View Post
Very interesting concept. Is there a recommended distance between the pieces of bracing (in your diagram, left hand side, distance from braces where they meet the side panel)? What about the recommended distance between full brace panels themselves - for example, on a larger 4 ft long box, how many brace panels would be required?
I haven't checked on this forum for a year or so (building snowmobile and writing a book). But I thought I'd answer you although it may be long since you decided. You can always add more bracing if you determine the need.

The maximum distance between bracing points depends primarily on four things:
-Panel thickness and panel material (ie how stiff the panels are).
-Upper frequency range of the enclosure.
-Volume you will be pumping out (decibels).
-Panel sizes (larger speakers with larger panels require more bracing).

lets take the worst case that require a ton of bracing:
An 80 liter speaker with 15" woofer that is expected to run between 100 and 1500hz, pumping out 130db at 1 meter with full power (1700 watts). To achieve this decibel output one needs minimal use of stuffing to maintain enclosure efficiency near port tune. To use very little stuff we need to use high strength panels of high density particle-board (the kind used for floors, when you tap them they ring like hardwood and they are extremely strong where they are glued together), that is 22-25mm thick (25mm is one inch).

With these requirements and this panel thickness and strength, I would not have more than about 3-4 inches between bracing points. Resulting in a difficult enclosure to brace properly, but it is possible, here's the woofer section:
Spoiler!

Note that I had to use some cross-bracing (white long pieces), which is inefficient, and problematic because you have to brace the braces, the cross braces now having surfaces more than 3-4 inches from bracing points. If I ran a resonance simulation you'd see the white cross-braces flop about like week old celery without something tying them together. Even the dark red/orange braces will need one brace running across them diagonally, but that can be a very thin brace. Or else we get this issue:
Spoiler!

Instead we want this:
Spoiler!


If I had the option I would have the rear panel be the opening and then brace the internal braces directly to the basket and magnet assembly of the speaker itself. The basket and magnet is the most solid piece in the entire speaker, its a shame not to use it for strength, but for this particular design I wanted the option to quickly change blown elements.

In this speaker the noise from the enclosure panels moving would be about 30db below the output of the speaker, at 1000hz. Lower db on lower frequencies. So that's a 30 db signal to noise ratio. Remember that the noise of the speaker itself will be reproduced by the speaker panels as well, 30db below the speaker output. And the noise from the panels not only comes off the external surfaces, but the internal ones, and hits the speaker surface internally, so it is reproduced to some degree by the speaker itself as well, especially where the distances coincide with certain frequencies. With this particular speaker the depth is about two feet if I recall correctly, and the speed of sound is just over 1000 feet per second so if this enclosure was just one foot deep it would need extra stuffing at the rear regardless of how strong the bracing is. It still likely needs a thin layer of stuffing at the rear panel since any frequency at about 1200hz or there about that lasts for more than two cycles will add to itself when it is reflected back.
Which is why REALLY expensive speakers are braced beyond belief or made by extremely solid materials like really thick polyester and glassfiber composites.
Compare the 30 db signal to noise ratio of the enclosure to the signal to noise ratio of the amplifier which is about 100db, which is why I basically ignore that spec on amplifiers, all that matters is that the amplifier can deliver the required wattage with better than or equal to 30db signal to noise ratio, in this case.

At 1000hz distortion is very audible to the human ear, so chances are if you slap together a system with any intention of going above 100db at those sorts of frequencies then it will probably be very unpleasant to listen to it without a very over-engineered bracing scheme. But if the bracing is well engineered, it could be possible to listen to the system at enormous volume without it being unpleasant. If the rear panel is slanted or split up into more than 1 face, you improve the reflective noise internally.

Too many invest in extremely expensive speaker elements and then spend no more time or effort to think through the bracing (window bracing, ugh, so inefficient, so hard to make, so difficult to scale beyond a couple window braces).

In a subwoofer on a very low frequency however, you can get away with murder, practically. But you quickly find out if you have enough bracing or not, by listening to the enclosure before putting stuffing in it. And feeling the panels. Any significant movement in the panels is going to make the bass sound washy and overbearing, rather than tight and controlled. Basically my rule of thumb with subwoofers for low frequencies is that I want to not be able to destroy the enclosure with a sledgehammer before giving up, so I make the enclosure and then brace it sufficiently with diagonal bracing so that I'd give up before the enclosure did. The bracing is also made from offcuts so its cheaper to brace than stuff it full of stuffing, just remember to glue (and MDF requires some screws or staples, because MDF is weak).

cms, aka driver diaphragm suspension mechanical compliance: 0.000065 meter/Newton or in standard form 6.5e-05 m/N. (smaller number is better)
rms, aka driver diaphragm suspension mechanical resistance: 6.41 Newton.sec/meter. (higher number is better)
ronny31 is offline  
Sponsored Links
Advertisement
 
Reply DIY Speakers and Subs

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page


Forum Jump: 

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