Throughout my career I have amassed a significant amount of knowledge on the subject of Statics. How this strength relates to frequency, however, I lack knowledge. I can run all the tensile sims in the world (and I do this weekly) but I don't have software to simulate resonances. I know it exists, but my question at the center of this thread is not about that software.
My questions is thus:
What is the difference between bracing and damping?
I see these terms intermingled when it comes to entering the dark realm of enclosure bracing. I see it said so many time that you can "brace a cabinet" or you can "brace it in order to dampen" it. These two things seem at odds with one another. At least to a standard manufacturing engineer such as myself. I understand both concepts, I just haven't even had a project where dampening of a structure was required to prevent cracking.
In this instance, we wouldn't be preventing cracking. We would be preventing a resonance. At least, that is my current understanding.
This leads to the second question:
What makes a brace act as a dampener as well as a brace?
My current understanding leads me to believe that a brace which could take a load but also flex would be best. Consider a solid board with a force axial to its length. A force entering into this board would simply transfer all of the load to its end.
Now lets consider a board with a bunch of holes in it. If we transfer a force into this board, yes, the force will go out the other end, however, some of it will be lost in flexion of the areas around the holes.
Is this correct or am I off by a lot here?
If we take multiple boards and cut various holes in them, stagger them, and intertwine them then we should be able to dampen and brace the cabinet all at once. Different size holes, different sizes of spaces between the boards, etc. This should spread out the loads, pressures, flexion caused by the forces from the drivers themselves.
While we are at it. Choose A or B here. I think B is probably better. A splits the enclosure in to 4 large pairs of sides where B splits it into many more differencing sizes. Choice B also makes it easier to make dimensionally on the table saw since the braces, top, and bottom are all the same width.
Option A
Option B
My questions is thus:
What is the difference between bracing and damping?
I see these terms intermingled when it comes to entering the dark realm of enclosure bracing. I see it said so many time that you can "brace a cabinet" or you can "brace it in order to dampen" it. These two things seem at odds with one another. At least to a standard manufacturing engineer such as myself. I understand both concepts, I just haven't even had a project where dampening of a structure was required to prevent cracking.
In this instance, we wouldn't be preventing cracking. We would be preventing a resonance. At least, that is my current understanding.
This leads to the second question:
What makes a brace act as a dampener as well as a brace?
My current understanding leads me to believe that a brace which could take a load but also flex would be best. Consider a solid board with a force axial to its length. A force entering into this board would simply transfer all of the load to its end.
Now lets consider a board with a bunch of holes in it. If we transfer a force into this board, yes, the force will go out the other end, however, some of it will be lost in flexion of the areas around the holes.
Is this correct or am I off by a lot here?
If we take multiple boards and cut various holes in them, stagger them, and intertwine them then we should be able to dampen and brace the cabinet all at once. Different size holes, different sizes of spaces between the boards, etc. This should spread out the loads, pressures, flexion caused by the forces from the drivers themselves.
While we are at it. Choose A or B here. I think B is probably better. A splits the enclosure in to 4 large pairs of sides where B splits it into many more differencing sizes. Choice B also makes it easier to make dimensionally on the table saw since the braces, top, and bottom are all the same width.
Option A
Option B
Isn't the function of bracing to stiffen, and thus drive the frequency of resonance above the range of concern?
And isn't damping just that, to damp resonance that will occur - by means of absorption and conversion to heat?
And isn't damping just that, to damp resonance that will occur - by means of absorption and conversion to heat?
Fascinating question really.
I wonder if it can be thought of, crudely, as bracing to stiffen materials, and dampening to slow air velocity. But I can see how they can be used intertwined with similar definitions, so context becomes crucial, especially with several translations, language barriers, etc. When I think of dampening, I think of filling, liner, etc, inside the enclosure so I think of it as air velocity related. But when I think of bracing, I think of it as a means to stiffen material so that it cannot resonate freely at lower band frequencies than the geometry of the panels that are braced/joined. So I would think, to your secondary line of thinking, it would be interesting to simple measure the board with and without the holes to see what happens with the transmission from one end to the other.
Very best,
I wonder if it can be thought of, crudely, as bracing to stiffen materials, and dampening to slow air velocity. But I can see how they can be used intertwined with similar definitions, so context becomes crucial, especially with several translations, language barriers, etc. When I think of dampening, I think of filling, liner, etc, inside the enclosure so I think of it as air velocity related. But when I think of bracing, I think of it as a means to stiffen material so that it cannot resonate freely at lower band frequencies than the geometry of the panels that are braced/joined. So I would think, to your secondary line of thinking, it would be interesting to simple measure the board with and without the holes to see what happens with the transmission from one end to the other.
Very best,
This is what I used to think. Let me share a video with you that will utterly destroy this false concept.
Yamaha clearly knows a lot more than I do about how Statics and frequencies work together
They are not bracing. A brace would just be a piece of metal. They are dampening. So it's a brace that is also a dampener. If it were just a brace then it would still ring, just at a higher frequency. That's the type of thing you want to avoid when building a cabinet. Raising the frequency higher and higher just moves the resonance, it does not eliminate it
The difference between bracing and bracing that dampens. This is what I'm trying to figure out how to do, just with wood instead of a dampener
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Would not bracing, designed to raise resonant frequencies, not help if you are applying it to a bass cabinet where the resonant modes are not excited by the driver ?
Use a softer, deader wood? Like using solid pieces of softer wood like 'big leaf' maple or some kind of poplar instead of Baltic birch plywood or another stiff plywood. That kind of idea...?
I should have specified that I want to do this mechanically, not with material choice. Plywood already has very good dampening ability. The only better material I have found is Petg-CF filament which edges it out by a small amount. Though with 3d printing you get to cheat by having a hollow interior with infill that naturally dampens
Watched the video and have to disagree with you.
It gets to be a semantic argument, mechanical dampers and material stiffeners . . . . . . . From the little I know, though they can be refined into technically sophisticated implementations, the two basic principles are distinct and fairly simple.
You are right, the second model of braces is better, option "B". Much better.
Bracing pushes up the resonance frequency. You want that, may it be a sub, full range or multi-way. So the question is why are higher resonances better? A very simple answer, the higher the frequency, the lower the speakers actual power input.. So you may put 25 Watt into a 35 Hz frequency, with the woofer rocking the whole room, but the spl not felt very high. Now look at the high mid: Even 2 Watt will be insanely loud, but noting in the room will vibrate. So the high frequency needs less power to satisfy the listener and hardly makes the cabinet resonate. Simply because it is so weak.
Look at it from another perspective: It is quite easy to suppress a high frequency, just a curtain will do, while the bass frequency will even be heard at the next house down the road, through walls. At the same level!.
So brace and lift cabinet resonances as high as possible, because they dont matter up there. The argument "..but you only push the resonance frequncy higher" is irrelevant.
Practical tests have shown that 10x10cm (4x4") open panel area is the best you can do. Anyway, any brace helps! So no need to go that small.
PS In the real world not anything more expensive is always better. Your sword made from pure gold will loose against cheap steel. Think about it. More money doesn't buy you the best in each case. So no need to make braces from exclusive high tec material. Some simple MDF or even particle board will do just fine.
Bracing pushes up the resonance frequency. You want that, may it be a sub, full range or multi-way. So the question is why are higher resonances better? A very simple answer, the higher the frequency, the lower the speakers actual power input.. So you may put 25 Watt into a 35 Hz frequency, with the woofer rocking the whole room, but the spl not felt very high. Now look at the high mid: Even 2 Watt will be insanely loud, but noting in the room will vibrate. So the high frequency needs less power to satisfy the listener and hardly makes the cabinet resonate. Simply because it is so weak.
Look at it from another perspective: It is quite easy to suppress a high frequency, just a curtain will do, while the bass frequency will even be heard at the next house down the road, through walls. At the same level!.
So brace and lift cabinet resonances as high as possible, because they dont matter up there. The argument "..but you only push the resonance frequncy higher" is irrelevant.
Practical tests have shown that 10x10cm (4x4") open panel area is the best you can do. Anyway, any brace helps! So no need to go that small.
PS In the real world not anything more expensive is always better. Your sword made from pure gold will loose against cheap steel. Think about it. More money doesn't buy you the best in each case. So no need to make braces from exclusive high tec material. Some simple MDF or even particle board will do just fine.
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Isn't damping usually more effective at higher frequencies too, because losses are usually higher?
Watch this one. It's like 2 minutes. This is good demonstration of the difference between bracing and dampening a mechanical structure.
You are right, increasing frequency (rigid bracing) is one thing and dumping is another.
Both methods can resolve the enclosure noise problem caused by resonances.
The enclosure panel is a kind of mass-spring system.
Mass is the mass of the panel and spring is the the panel rigity to restore itself to the original shape after being flexed by an external force, in this case, air pressure from speaker.
When we add rigid braces, we increase the spring stifness (k) and this increases the resonance frequency.
We are not dumping.
Of course that a panel has some sort of damping, cause wood flexing also has resistance and dissipates energy as heat.
This is ideal mass-spring
This is dumped mass-spring (in this case dumping provided by a fluid)
If you don't want to change the resonance frequency but just dump the panel, you need to add an extra element to the system: dissipation element.
So, the frequency will not change, but the system will quickly stop moving (dumped system).
This is what happens when you add a shock absorber to a car or motorcycle: you don't change the system resonance frequency, but just dump the system.
In order to only dump the enclosure panels, some material that converts movement to heat (not necessarily but most common) needs to be added to the panels or to the elements that connect one panel to the other.
When they move, this material will dissipate the movement energy to heat and stop the movement.
This is school theory - Now let's see the practical solutions, which I'll only guess 🙂
Pratically, you can apply layers of more plywood to the panels with some flexible material in between (this is the resistance that will dissipate the energy) or connect the braces between opposed panels not rigidly, but by some means of a material that will add this movement resistance (some kind of rubber or high viscosity fluid, for example). It can be complex and expensive.
So this is inline with about what I thought. One idea I had was to 3d print braces. Install the braces with a foam or rubber between them and the panels.
Alternatively, I could 3D print the braces such that they had some sort of "spring" mechanism in them that would dissipate the energies. Of course, this could totally backfire and causes massive resonances of itself. A variable coil could possibly work. My track car has dual rate springs. Not progressive but actually two different spring rates connected to the damper itself. You could put different spring rates all around and end up with a mass of overlapping spring rates that could take up resonances.
Enclosure resonances are a function of inner dimensions of the enclosure vs. frequency generated by the speaker. A very stiff enclosure will provide the standing wave perfect reflection to express itself. With a less stiff enclosure, the walls themselves will actually somewhat dampen the resonance.
That, at least, is correct. And it's very cheap, effective, and has little to no drawbacks, which it why it should always be used; except perhaps in subwoofers, where the first enclosure resonance may be several octaves above the crossover frequency.
If you run tensile sims on a weekly basis, you should be able to run modal analysis as well. It is a basic analysis to check the structure's resonant frequencies. Resonant frequencies are calculated from material properties (density, poisson, and Young modulus) based on the geometry.
I highly recommend trying it, because bracing without calculation is like shooting blind, since every brace you add will increase the mass of the structure, which can increase the deformation at the resonant frequency.
When I built my speaker, I played days to optimize the bracing, then I validated the calculation with an accelerometer attached to the walls, and I have to say, the calculation was surprisingly close to the measurement.
Bracing means adding material to increase the stiffness of a structure. Damping is a force that opposes motion. They are different things that aren't comparable. The relevant forces involved in a vibrating structure are stiffness, damping and inertia/mass. The type and placement of material can be used to increase or decrease the size of these forces which vary differently with frequency in both phase and magnitude.
A brace is a strut intended to add stiffness. A strut intended to add damping (e.g. a damper in a car) would not be called a brace because it's purpose is not to stiffen.
All materials have mass, stiffness and damping. Stiff materials tend to have low damping and materials with high levels of damping tend to have low stiffness. High(ish) stiffness and high(ish) damping is usually achieved with composite materials.
In order to reduce the level of unwanted radiated sound a cabinet requires different levels of stiffness, damping and mass in different places. DIYers often seek to brace the hell out of everything (e.g. your pictures) in the belief that a stiffer structure will radiate less unwanted sound. This is not a correct assumption. Cabinets designed by engineers in engineering-lead rather marketing-lead speaker companies tend to look rather different.
So where should a cabinet be stiff? Where should it have high damping? Where should it be heavy?