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post #61 of 337 Old 02-06-2016, 07:05 PM
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Is anyone here familiar with the square-cube law and the size effect?
We make an 8" LCR enclosure with 22mm mdf and that's probably great, probably the strongest enclosure for miles.
Then we take 22mm mdf to make a 15" subwoofer enclosure, and the dinosaur bones cracks under its weight. To borrow a metaphor. Lets assume they put out as much db each, only at different frequencies. They both output 110db lets say, and lets say have a 120db internal sound pressure. That's 20 Pascals of pressure (atmospheric pressure around you is 101 325 Pascal, so its a very tiny pressure difference, but its 20 pascal above and below the atmospheric average).
Now, in the 8" enclosure, the relative surface area inside the enclosure, and the thickness of the material, means its very strong. So there's very little give in the surface. Lets say the enclosure is just 9" by 14" by 9" deep. With nearly 1" thick material.
With the 15" subwoofer enclosure however, the cross-section strength of the material is the same (or even double) but the surface area is x^2 larger, so even the tiny 40 Pascal peak to peak pressure difference, is enough to potentially make the surfaces move. it may be 18" by 28" by 18". Even with double the thickness, so two 7/8 inch sheets, its still under strength relative to the 8" enclosure. By a lot. Because the 40 pascal peak to peak pressure difference acts on a surface area that is x^2 larger. And the dimensions of the sheets are twice as big in two directions. If you had some reinforcement in the 8" enclosure, and duplicate it in the 15" enclosure, the 15" enclosure is still understrength compared to the 8" enclosure. Because you need relatively more reinforcement compared to the 8" enclosure.
If the enclosure isn't only bigger than a smaller counterpart, but also louder, it further increases the need for relatively out of proportion more strength. If you go +6db up its a doubling in Pascal, by the way. Which is multiplied by the x^2 larger surfaces. Its the reason why extreme db drag cars are built like bunkers on wheels throughout, from the enclosure to the compartment they are trying to get insane db in.

So you need reinforcement. But how much?
How much you require is dependent on frequency. To make 40 pascal peak to peak at low frequency you need a lot of cone movement, and subsequently you need a lot of enclosure movement to lose db with low frequencies.
But to make 40 pascal peak to peak at high frequencies, may not even require the surface to move enough for your fingertips to feel the movement. If you have ever touched a very high frequency driver, you know what I'm talking about.
So, on subwoofers, if you reinforce until you no longer detect movement with your fingers, its as strong as you could ever need to make it.
But with LCRs, there's no limit to how strong you would have them in an ideal world where you can have anything you want. There's only the compromise between cost and benefit. I can't say where you should make that compromise, what is right compromise for you is the right compromise for you. But to dismiss the idea seems to me that you are unaware that you made a compromise in strength. The reason I've tried to stick with this thread is to try to make some people who read this aware of the compromise so that they can best make it.

If I had my will I would build big LCR enclosures for 15" drivers from pre-made 50mm thick woven glassfiber-composite sheets, but the factors involved in my compromise includes cost limitations, and 50mm glassfiber sheets aren't too cheap to ship to the end of the world. A few kilograms of resin and fiberglass mats however, isn't too expensive.

The size effect has to do with faults in the material which affect its strength negatively. If you double up with cross-section in a beam it will fail before double stress. And that's if the beam is manufactured for load-bearing structures. Mdf is not held to a standard of strength or uniformity of strength. Because its not used for load-bearing structures, just some furniture, wall covering, ceiling tiles and speaker enclosures and such. So the addition of strength when adding more mdf is even worse than if you for example doubled up with 2" by 4" load-bearing wood beams.
Even the high density particleboard I use isn't perfect, but its used for load-bearing floor-boarding so its held to a regulated standard of uniformity and strength. Only one person had to go through the floor one day to make sure no sheet leaves the factory if it isn't up to a certain standard in uniformity and strength.

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post #62 of 337 Old 02-06-2016, 07:39 PM
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Originally Posted by ronny31 View Post
Is anyone here familiar with the square-cube law and the size effect?
We make an 8" LCR enclosure with 22mm mdf and that's probably great, probably the strongest enclosure for miles.
Then we take 22mm mdf to make a 15" subwoofer enclosure, and the dinosaur bones cracks under its weight. To borrow a metaphor. Lets assume they put out as much db each, only at different frequencies. They both output 110db lets say, and lets say have a 120db internal sound pressure. That's 20 Pascals of pressure (atmospheric pressure around you is 101 325 Pascal, so its a very tiny pressure difference, but its 20 pascal above and below the atmospheric average).
Now, in the 8" enclosure, the relative surface area inside the enclosure, and the thickness of the material, means its very strong. So there's very little give in the surface. Lets say the enclosure is just 9" by 14" by 9" deep. With nearly 1" thick material.
With the 15" subwoofer enclosure however, the cross-section strength of the material is the same (or even double) but the surface area is x^2 larger, so even the tiny 40 Pascal peak to peak pressure difference, is enough to potentially make the surfaces move. it may be 18" by 28" by 18". Even with double the thickness, so two 7/8 inch sheets, its still under strength relative to the 8" enclosure. By a lot. Because the 40 pascal peak to peak pressure difference acts on a surface area that is x^2 larger. And the dimensions of the sheets are twice as big in two directions. If you had some reinforcement in the 8" enclosure, and duplicate it in the 15" enclosure, the 15" enclosure is still understrength compared to the 8" enclosure. Because you need relatively more reinforcement compared to the 8" enclosure.
If the enclosure isn't only bigger than a smaller counterpart, but also louder, it further increases the need for relatively out of proportion more strength. If you go +6db up its a doubling in Pascal, by the way. Which is multiplied by the x^2 larger surfaces. Its the reason why extreme db drag cars are built like bunkers on wheels throughout, from the enclosure to the compartment they are trying to get insane db in.

So you need reinforcement. But how much?
How much you require is dependent on frequency. To make 40 pascal peak to peak at low frequency you need a lot of cone movement, and subsequently you need a lot of enclosure movement to lose db with low frequencies.
But to make 40 pascal peak to peak at high frequencies, may not even require the surface to move enough for your fingertips to feel the movement. If you have ever touched a very high frequency driver, you know what I'm talking about.
So, on subwoofers, if you reinforce until you no longer detect movement with your fingers, its as strong as you could ever need to make it.
But with LCRs, there's no limit to how strong you would have them in an ideal world where you can have anything you want. There's only the compromise between cost and benefit. I can't say where you should make that compromise, what is right compromise for you is the right compromise for you. But to dismiss the idea seems to me that you are unaware that you made a compromise in strength. The reason I've tried to stick with this thread is to try to make some people who read this aware of the compromise so that they can best make it.

If I had my will I would build big LCR enclosures for 15" drivers from pre-made 50mm thick woven glassfiber-composite sheets, but the factors involved in my compromise includes cost limitations, and 50mm glassfiber sheets aren't too cheap to ship to the end of the world. A few kilograms of resin and fiberglass mats however, isn't too expensive.

The size effect has to do with faults in the material which affect its strength negatively. If you double up with cross-section in a beam it will fail before double stress. And that's if the beam is manufactured for load-bearing structures. Mdf is not held to a standard of strength or uniformity of strength. Because its not used for load-bearing structures, just some furniture, wall covering, ceiling tiles and speaker enclosures and such. So the addition of strength when adding more mdf is even worse than if you for example doubled up with 2" by 4" load-bearing wood beams.
Even the high density particleboard I use isn't perfect, but its used for load-bearing floor-boarding so its held to a regulated standard of uniformity and strength. Only one person had to go through the floor one day to make sure no sheet leaves the factory if it isn't up to a certain standard in uniformity and strength.

Put simply, an 18" by 18" panel with a center dowel cross brace acts as (4) 9" by 9" panels with their adjacent corners supported by he dowel, and the other corners supported by the remaining sides of the box. Importantly, the other end of the dowel is connected to the opposing side of the box. When one side receives 40 Pascals of pressure, so does all the other sides. Because the panels are connected to each other by the dowel(s), the forces act in opposite directions, canceling out each other at the panels. It is the dowel(s) tensile strength (and some glue) that withstands those forces, not the sides.
EDIT: The dowel(s) simply need to be spaced close enough for the forces involved. For larger panels, increase the number of dowels (braces). Using MDF strips for the braces works because MDF has enough tensile and compressive strength, even though it is weaker in flexural strength. It's also much cheaper to build specifically for the forces involved, and with materials already at hand.

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post #63 of 337 Old 02-06-2016, 07:57 PM
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Quote:
Originally Posted by Augerhandle View Post
Put simply, an 18" by 18" panel with a center dowel cross brace acts as (4) 9" by 9" panels with their adjacent corners supported by he dowel, and the other corners supported by the remaining sides of the box. In addition, the other end of the dowel is connected to the opposing side of the box. When one side receives 40 Pascals of pressure, so does all the other sides. Because the panels are connected to each other by the dowel(s), the forces act in opposite directions, canceling out each other at the panels. It is the dowel(s) tensile strength that withstands those forces, not the sides.
You put it too simply.
If you used your own hand to reinforce the surface, like is done on windshields and roofs on cars in db drag sometimes, then there's still give in your flesh and bones. So adding the dowel doesn't eliminate the movement at the point where you place the dowel. How much elimination of movement you get, is proportional to the strength of the materials used. Steel plate reinforced with steel plate is very conducive to getting lots more strength from this reinforcement method. If you use a steel piece to reinforce mdf however, you don't get this idealized elimination of movement at the point where you placed it. The give in the mdf contact patch is not eliminated, you can compress and extend the mdf material itself at the contact patch, like the flesh on your hands trying to stop a windshield popping out during a db drag run (well actually, for it to be just like your hands against a windshield we'd need to glue your hands to the windshield, and given that the windshield travel can be up to 4-5 inches, you would get your skin ripped off. Imagine what happens on a microscopic level with a dowel connected to a piece of mdf).
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post #64 of 337 Old 02-06-2016, 08:07 PM
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Quote:
Originally Posted by ronny31 View Post
You put it too simply.
If you used your own hand to reinforce the surface, like is done on windshields and roofs on cars in db drag sometimes, then there's still give in your flesh and bones. So adding the dowel doesn't eliminate the movement at the point where you place the dowel. How much elimination of movement you get, is proportional to the strength of the materials used. Steel plate reinforced with steel plate is very conducive to getting lots more strength from this reinforcement method. If you use a steel piece to reinforce mdf however, you don't get this idealized elimination of movement at the point where you placed it. The give in the mdf contact patch is not eliminated, you can compress and extend the mdf material itself at the contact patch, like the flesh on your hands trying to stop a windshield popping out during a db drag run (well actually, for it to be just like your hands against a windshield we'd need to glue your hands to the windshield, and given that the windshield travel can be up to 4-5 inches, you would get your skin ripped off. Imagine what happens on a microscopic level with a dowel connected to a piece of mdf).

You are forgetting one thing: Using dowels or MDF bracing WORKS. There is no need to build steel boxes with I-beam reinforcements welded to AWS D1.1 specification.


Also you keep talking about SPL drag races, which is off the topic and intent of this thread. You might as well quote shipbuilding techniques, it'd be as relevant.
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post #65 of 337 Old 02-06-2016, 08:35 PM
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Maybe your MDF is made from Norwegian wood.


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post #66 of 337 Old 02-06-2016, 08:58 PM - Thread Starter
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Quote:
Originally Posted by Augerhandle View Post
Put simply, an 18" by 18" panel with a center dowel cross brace acts as (4) 9" by 9" panels with their adjacent corners supported by he dowel, and the other corners supported by the remaining sides of the box. Importantly, the other end of the dowel is connected to the opposing side of the box. When one side receives 40 Pascals of pressure, so does all the other sides. Because the panels are connected to each other by the dowel(s), the forces act in opposite directions, canceling out each other at the panels. It is the dowel(s) tensile strength (and some glue) that withstands those forces, not the sides.
EDIT: The dowel(s) simply need to be spaced close enough for the forces involved. For larger panels, increase the number of dowels (braces). Using MDF strips for the braces works because MDF has enough tensile and compressive strength, even though it is weaker in flexural strength. It's also much cheaper to build specifically for the forces involved, and with materials already at hand.
Nice explanation, I was thinking about bracing almost like I was laying out floor joists but I see where that is wrong. The two opposing panels are pushing or pulling in unison so more contact points (dowels) the better the better the brace in this situation to take advantage of the cancelation. Thanks Bob
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post #67 of 337 Old 02-06-2016, 10:26 PM
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Quote:
Originally Posted by Augerhandle View Post
You are forgetting one thing: Using dowels or MDF bracing WORKS. There is no need to build steel boxes with I-beam reinforcements welded to AWS D1.1 specification.


Also you keep talking about SPL drag races, which is off the topic and intent of this thread. You might as well quote shipbuilding techniques, it'd be as relevant.
Between the spectrum of projects that require zero bracing and infinite bracing, mdf works in one portion of this spectrum. But as we know, on this forum tons of builds reach the extremes of that spectrum. For those mdf doesn't really cut it. It CAN with the right design, but at a certain point they're better off going away from mdf-centric designs.

Db drag racing is a nice way to show people what happens on a microscopic level, since the db levels make it macroscopic and easy to spot.
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post #68 of 337 Old 02-07-2016, 05:51 AM
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Quote:
Originally Posted by ronny31 View Post
Between the spectrum of projects that require zero bracing and infinite bracing, mdf works in one portion of this spectrum. But as we know, on this forum tons of builds reach the extremes of that spectrum. For those mdf doesn't really cut it. It CAN with the right design, but at a certain point they're better off going away from mdf-centric designs.

Db drag racing is a nice way to show people what happens on a microscopic level, since the db levels make it macroscopic and easy to spot.
Can you share some info on how the bass extremists build their cabinets? Most of what I have seen are 4th order walls that produce one note and mostly have no bracing other than a metal rod or two.
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Nice explanation, I was thinking about bracing almost like I was laying out floor joists but I see where that is wrong. The two opposing panels are pushing or pulling in unison so more contact points (dowels) the better the better the brace in this situation to take advantage of the cancelation.
This picture shows the end on view of braces connecting two panels. If the panels are 1/2" thick the addition of the red brace increases the panel stiffness to the equivalent of 1" thick panels. The further addition of the blue braces increases the panel stiffness to the equivalent of 2" thick panels.
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post #70 of 337 Old 02-07-2016, 06:32 AM
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I've used 1" hardwood dowels for bracing, polyurethane glue, and a screw into the end of the dowel. Can't beat the
ease of making a dowel brace, and it is highly effective.


No reason you can't mix shelf type bracing and dowels, if you don't care about the finished size of the cabinetry.


I'm not even sure about the dowel versus shelf bracing comments. A shelf brace does use up internal volume, but it does produce
an T cross section which would be a highly effective form of bracing, when glued along it's entirety. But a hardwood dowel brace
is one chop saw cut.


What I am not seeing, is the baffle doubled up, in all the illustrations.
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post #71 of 337 Old 02-07-2016, 06:41 AM
 
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What I am not seeing, is the baffle doubled up, in all the illustrations.
It's not necessary, unless you're using a backing piece to allow flush mounting of the driver. Bracing the baffle to the back is sufficient, which is shown in my first illustration back on the first page. In that illustration the effective thickness of the baffle is tripled. When the braces do double duty as the securing points for the driver mounting screws the driver frame is rendered immobile.

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I would assume that in car audio, the only thing that matters is max spl. Sound quality is a term that is not even used or considered. Just get the bass as loud and obnoxious as possible. Stock speakers + 140 dB of bass rattling the car apart is just right. Who cares if the cab vibrates...the whole car is rattling anyways.
Then you assume incorrectly. SPL contests are just that, contests. However, IASCA and the other organizations had "sound-off" competitions that had judges for installation technical quality, sound quality, innovation and used RTA to determine frequency response. Sound quality covered imaging/sound stage, smoothness of response and when some systems came through the line, many were very impressive for their spaciousness, reality and balance. These systems often had many subwoofers, but if someone wants to hear balanced sound when the whole listening environment is making broadband noise that obscures the low end unless the system can overcome this, you just won't hear it. The systems with the best sound will have more output in the low end than is needed when the car is stopped and the engine isn't running, but while driving, it sounds better than you might imagine. The boxes and panels on doors need to be as rigid as possible and that can't happen unless they're properly braced. It's impossible to achieve predictable response if the cabinet isn't braced and when someone builds a DIY system, they can afford to follow "If at first you don't succeed, try, try again" but for those of us who did it professionally, the results had better be pretty good or great, or we would never have survived as a business. Also, the box couldn't always occupy the whole trunk, either.
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Which makes me want to ask how you are mounting the driver?


T-nuts or some sort of embedded threaded insert?
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post #74 of 337 Old 02-07-2016, 07:01 AM
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Here's my preferred method to stiffen the cabinet.

Grey is the wood material, black is polyester/epoxy resin, orange is sticks. First the grey surface is coated with resin, then the sticks are applied, then ideally I also use some chopped mats glassfiber and add it on top of the whole thing over the sticks and between them when I apply the resin on top of the sticks. The sticks go the long axis of the surface they reinforce. For db drag I would use a lot of glassfiber and the distance between the sticks would be smaller than a home-stereo speaker. Home speakers may do just fine with only one layer of glassfiber, and on the smallest surfaces no glassfiber at all.
This works even on LCR speakers, because you don't need tons of stuffing to avoid high frequency sounds coming out of the ports, just a 1 inch or 5/6 inch layer of stuffing on all the internal surfaces.
From this diagram, you're doing nothing to prevent flexing across the panels in both directions (X and Y) and that's a problem unless the narrow dimension is small. The problem with wide, flat materials is due to the moment of inertia- the force at the center is really trying to force the panel to rotate and the edge joints act as the pivot. Attaching opposite panels resists this rotation by coupling them and the force acting on one side is resisted by its stiffness and when bracing is added, the other adds its own resistance.

MDF is far from being like moist sand. The good type is hard, stiff and highly machinable. I's not sure you know what it is. As mentioned, it can be cut cleanly enough that the edge will cut skin that isn't particularly delicate.
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post #75 of 337 Old 02-07-2016, 07:17 AM
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Which makes me want to ask how you are mounting the driver?


T-nuts or some sort of embedded threaded insert?
If you're asking me, what is needed depends on the diameter of the driver and the number of screw holes. T-nuts are great if the driver will be installed and never removed but screwing directly into MDF is a tried and proven method, even over many years of heavy use. One determining factor is the weight of the driver and the forces the cabinet is exposed to. If it's never moved, screws are fine and if it's moved frequently, I would use some additional mechanical device, like T-nuts, threaded inserts, etc. The thread of a screw into MDF, particle board or plywood needs to be coarse, or the force exerted in tightening will shear the fibers and they won't hold. Also, more screws means more force will be required to pull the screws out and if the force is on the driver's axis, they share the load equally, assuming it's a homogeneous material. The screws also need to penetrate far enough to use the parallel area of the threaded shank to prevent it pulling out. I have seen subwoofers installed using 1/2" or 3/4" drywall screws into 3/4" particle board (mostly pre-made boxes) or MDF and for a smaller woofer that isn't exposed to a lot of power, they're fine. Unfortunately, they were usually used for large woofers in high power systems. A 1" coarse drywall screw needs a good amount of force to shear the fibers in MDF and because it tends to separate in layers, longer screws are needed. If one screw requires 50lb, six or eight screws will certainly hold a smaller woofer and any mid or tweeter. 12" or larger and I like to add a layer around the hole, so I can use longer screws and make it a bit stiffer or, as is often needed for PA/musical instrument drivers, some kind of metal insert that survives repeated removal and replacement of the screws.
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Which makes me want to ask how you are mounting the driver?
I use screws. If the driver is heavy I'll add some small plywood blocks to the back of the baffle for better retention, unless the screws go into braces, in which case they're not going anywhere.
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post #77 of 337 Old 02-07-2016, 07:27 AM
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Strength isn't required in a speaker panel. The forces are quite small. Stiffness, mass, and damping are needed, probably in that order. MDF is particularly good when it comes to mass and damping. Damping isn't a big factor in the bass region, but itnplays a nontrivial role in higher rolloff frequencies above XO and especially with distortion products.

There are stiffer materials to use for paneling, but they aren't necessary since bracing is a much much much more effective method of stiffening a panel than increasing either thickness or modulus.

DB dragrace guys are mostly misguided. Except that joint strength becomes a real factor and that's where grp can help. Of course simple blocking is cheaper and equally effective.
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post #78 of 337 Old 02-07-2016, 07:28 AM
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Quote:
Originally Posted by corradizo View Post
Can you share some info on how the bass extremists build their cabinets? Most of what I have seen are 4th order walls that produce one note and mostly have no bracing other than a metal rod or two.
In an SPL contest, a "one note wonder" is fine but for a car system that's made for listening to music, that doesn't work. However, a 4th order cabinet tuned to 40Hz still provides some usable energy at 20Hz and 80Hz and in use, a 4th order box tuned to one frequency sounds like crap. In a system designed for music, it would be far better to tune it to ~35Hz and 80-100Hz, so peaks can be decreased and the car's noise floor can be simulated, but at a higher SPL. Some of the woofers used required a small box that often had a clear plexy/Lexan panel, to show everyone how awesome the installer was, with speckled paint on all of the panels. Some of them actually sounded good but they weren't as good as the ones that were properly braced. It's easy enough to find the resonances by using a frequency generator and attaching a transducer to it but I don't remember seeing or hearing about anyone doing that before I stopped doing car audio in '97. It's also easy to feel the panel as it vibrates when the frequency sweep occurs slowly and the problem frequencies cause flexing and audible resonances that seem to come from nowhere.
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Originally Posted by Bigus View Post
Strength isn't required in a speaker panel. The forces are quite small. Stiffness, mass, and damping are needed, probably in that order. MDF is particularly good when it comes to mass and damping. Damping isn't a big factor in the bass region, but itnplays a nontrivial role in higher rolloff frequencies above XO and especially with distortion products.

There are stiffer materials to use for paneling, but they aren't necessary since bracing is a much much much more effective method of stiffening a panel than increasing either thickness or modulus.

DB dragrace guys are mostly misguided. Except that joint strength becomes a real factor and that's where grp can help. Of course simple blocking is cheaper and equally effective.
WRT 'strength', the material still needs to stand up to what it's exposed to- I wouldn't consider cardboard a strong material but MDF is. As far as the forces involved, I have seen sub boxes that came apart at the seams from the user treating the system like a farm animal, but those were usually just butt joints with wood glue and box staples when someone cranked it before the glue dried. Never with screws and never with dado/groove joints & wood glue that had dried/cured.

Less is more unless wide panels are involved.
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post #80 of 337 Old 02-07-2016, 07:51 AM
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Originally Posted by corradizo View Post
Can you share some info on how the bass extremists build their cabinets? Most of what I have seen are 4th order walls that produce one note and mostly have no bracing other than a metal rod or two.
What most use is irrelevant, what most winners use is steel reinforcement directly on the chassis which is then filled in with fiberglass and concrete (concrete ceilings and walls is getting popular, with internal steel mesh wired in place first its really easy to do, just lay the concrete with the car on the side or roof, no form needed and you use all the space out to the edge of the chassis panel). Steel beams you see are there in addition to this reinforcement you don't see, because the largest surfaces (roof and floor) will flap like a bird under 170db+ even if they're made of steel, fiberglass and concrete. The steel beams that cross the space will be bolted through the floor and ceiling with the same bolts as the doors. And act both as a pre-tensioned steel wire and load-bearing column depending on which way the pressure is trying to force the surfaces in that particular fraction of a second. Though the steel beams are bolted to the steel beams inside those surfaces, they aren't just bolted to bare chassis skin as surface braces like we do with mdf. If you are to use bracing on mdf, you should at least double up the mdf at the contact location, or glue real wood to the surface you are bracing (or plywood), so that the force isn't concentrated on one tiny patch of mdf. Every little unit of volume you waste with the bracing will have much greater effect then.
Back to db drag: The doors are bolted in place with 10-12 inch long 1/2 inch bolts. The windows are 3+ inch thick bolted into 1/2 inch thick steel frames.
Since the enclosure makes up about half the internal vehicle volume that they are trying to pressurize with db, most enclosures are made with the level of strength as the rest of the cabin. If the doors are bolted in place with half a dozen or more 1/2 bolts, what does that tell you about the enclosure strength? :P Db drag winners are insanely aware that db will escape through the easiest path, so they constantly improve on the weakest link in strength. And anything that isn't shaking in timing with the cones, isn't producing the db that will tick them over the world record, so they try to eliminate it.
They build enclosures like we would build an armored car, we build enclosures like they would build a bookshelf.

There are of course those here who take the step to build bunker-busting enclosures.
This one is about as strong as you can make an enclosure with wood. At like page 11 you see the reinforcements and stuffing.
This enclosure is probably at the border between when it may be less work and cost to just plaster the inside with polyester and glassfiber. But this particular person knows wood-working and had all the tools for it so it was easier for that person to do it this way with complex bracing than to learn glassfiber composite techniques. If someone fixed his canoe and then built this, he would probably end up just laying a quarter inch of glassfiber and resin on the inside of the plywood like this:

black is resin and glassfiber, orange is sticks for adding thickness to the glassfiber without having to fill it completely in (a cost saving technique which costs a little time in laying the mats). Grey is the plywood.
But this guy did it right. He uses plywood not mdf, he even laminates it further, he uses evenly spaced plywood bracing, he bends two of the largest surfaces twice in an S shape. Its essentially a wooden composite enclosure, wood sheets instead of (glass)fibers, with glue holding it together (epoxy/polyester resin is just fancy names for glue). But, given the time he spent making the reinforcements it may have been as quick and easy for someone equally skilled in glassfiber, to reinforce equally much (or even more) with glassfiber. So if he was a modern boat-builder he would probably have used glassfiber, but since he knew wood-working he used (the correct) wood.
With such a driver, you could probably not make it weaker, or it would flop like a plastic bag. Don't forget, relative to the cone size, its as if we built a 10" subwoofer with something like 4mm plywood. Without all that bracing, it wouldn't work. If it was mdf, it probably wouldn't work.

EDIT: FYI, this method in the picture does strengthen the material even in the direction perpendicular to the sticks. Because the glassfiber is thicker where the sticks are and that reinforces the thin bits between the sticks. You may of course run sticks along the short length instead of the long length so that you have more reinforcement, but then you spend more time on it and may ultimately get more reinforcement in a days work by working with bigger pieces (longer sticks, larger diameter sticks, more space between the sticks, thicker glassfiber mats)(glassfiber mat thickness is proportional to the sharpness of the shapes you want to push the glassfiber into and around).

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post #81 of 337 Old 02-07-2016, 08:19 AM
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Ronny31,
Do you have a link to a car audio build of someone doing what you mentioned? I've never seen anything that crazy.
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I've never seen anything that crazy.
Try this:
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post #83 of 337 Old 02-07-2016, 09:24 AM
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I don't skulk in db drag forums, they tend to not share their good tricks anyways. But if you take a look in a db drag event you can tell which have done most prep work in strengthening the car and predict who will do well almost independently on how much they spent. Here's two example videos from a quick google search, notice all the painted-over bolt-heads everywhere (the ceiling, floor etc).
6:30 in this:
14:40 in this:
Tried to get the videos to start at those locations but the forum is s***.
Don't know of any Norwegians who compete in the top bracket, most of the people who turn up for competitions here just have two very expensive subwoofers and one expensive amp with some expensive branded asphalt mats everywhere. Because that's what is cool at the moment; That the A-pillars give in over time so that the beam between them eventually becomes a wiggly piece of tin. Great for hitting moose. Not.

EDIT: The encabulator bit is especially good when he says "refer to the manual and songbook" XD

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post #84 of 337 Old 02-07-2016, 10:16 AM
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I've seen, and felt, plenty of big systems, but I haven't seen or heard of anyone using concrete. I was wondering if you had a link to someone doing that.
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post #85 of 337 Old 02-07-2016, 11:25 AM
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Google. I have no idea where to find build threads for db drag cars. There's no big AVSforum-alike full of build threads as far as I'm aware. Last time I witnessed a concrete reinforced db drag car my phone didn't have a color screen let alone a camera.
Btw, you weren't allowed to sit inside this one when it went full blast. They only gave it 1/4 wattage when you sat with the door open on the floor (no seats) and never closed the door (it would have to be bolted in place). To call it a "system" is a bit strange, its a bunker on wheels that they push around and bring on a trailer. Inside it are many electromagnetic linear actuators that compress and rarefy the atmosphere in order to compete for the highest Pascal difference above and below the atmospheric pressure.
Something similar would be to bring an armored vehicle with no engine on a trailer with you to certain audio events and then blow up hand-grenades inside it while its closed while you look at a meter which measures how much of the energy the vehicle contained.

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post #86 of 337 Old 02-07-2016, 11:47 AM
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I'm going to eject from this nonsense. Next time Pascal is promoted as "word of the week" on dictionary.com, could someone please post a warning? I hope the OP got what he needed.
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post #87 of 337 Old 02-07-2016, 11:51 AM
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Yeah, crazy stuff. Craig Butler has hit over 182. I think that's the current world record.
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post #88 of 337 Old 02-07-2016, 01:26 PM
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Here's Albert Von Schweikert's take on speaker design. http://www.vonschweikertaudio.com/#!designer-bio/cjbm
Notice that he favors constrained layer damping in his speakers. I don't think that it can argued that he, a Cal- Tech trained engineer, hasn't done the research to support his theories on speaker design and his speakers have been very successful in the marketplace.

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post #89 of 337 Old 02-07-2016, 07:02 PM
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Originally Posted by rajacat View Post
Here's Albert Von Schweikert's take on speaker design. http://www.vonschweikertaudio.com/#!designer-bio/cjbm
Notice that he favors constrained layer damping in his speakers. I don't think that it can argued that he, a Cal- Tech trained engineer, hasn't done the research to support his theories on speaker design and his speakers have been very successful in the marketplace.





It is interesting that he compares his product to the "industry standard"-MDF. Usually, something becomes industry standard for very good reasons.
Quote:
...compared to a solid cabinet made from the industry-standard MDF (medium density fiberboard)...

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post #90 of 337 Old 02-08-2016, 04:44 AM
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