double/triple layering

[DarkTinman 9]

Alright, well as stupid as this Topic sounds, i have had a lot of questions from other people and myself. When you are building a box we all know that people don't just use 1 layer of MDF, they use 2-3 in heavy applications. In my instance, building a wall.

So when i first started thinking/building my wall, i asked a older friend of mine (who is an aerospace engineer) to help me with building this. The only reason i add this in is to try and explain that he isn't a complete idiot. He also explained to me that because he works with airplanes he understands the concept of how vibrations cause things to break and how things have to be sealed. Not only that but he is very crafty with woodwork.

Now on to the question, in talking to him i tried to explain that we need to double layer or maybe even triple layer the box we were building. He went on that to explain that the wood doesn't need all of that extra layers and that with proper bracing that we wouldn't need to double or triple any layers because with the layering it doesn't actually strengthen it, it would only help deaden

So my question is this, can someone please explain what layering does and why it's needed. Other then just "Yeah, you always need to layer."

I am looking for some actual answers please!

Edited March 14, 2011 by DarkTinman

[Godsmack 360]

In my experience (while limited) it does help strengthen it. I think of it this way, when you add bracing it helps take some of the impact of the force of the cone's movement and absorbs it. Adding more than one baffle helps absorb some of this impact. This takes away from the flex in the wood, in similar way that proper bracing would. A stronger box makes for better resistance to pressure.

If a ninja can barely break one board with 1/10th of his force and one chop, could he break 3 boards with the same amount of chops and the same force? No. He would need multiple chops. Same principle with wood for speaker boxes. More layers will help make it more durable.

J

[hondakilla98 29]

Did you explain to him that the layers would be glued together? Effectively making one piece of mdf that is 2-3 times as thick.

[///M5 2,833]

Obviously he forgot to take a structures class. That being said don't assume that a box with no flex won't be louder than one that does, but you can always expect that a box with minimized flex will color the sound less.

[Duran 387]

I'd rather brace, much less weight, and an unmeasurable amount of loses vs. layering.

[DarkTinman 9]

In my experience (while limited) it does help strengthen it. I think of it this way, when you add bracing it helps take some of the impact of the force of the cone's movement and absorbs it. Adding more than one baffle helps absorb some of this impact. This takes away from the flex in the wood, in similar way that proper bracing would. A stronger box makes for better resistance to pressure.If a ninja can barely break one board with 1/10th of his force and one chop, could he break 3 boards with the same amount of chops and the same force? No. He would need multiple chops. Same principle with wood for speaker boxes. More layers will help make it more durable.J

Yeah i understand what your saying. That makes sense too but at the same time i don't think i completely understand or am grasping what exactly the "scientific" answer is...

Did you explain to him that the layers would be glued together? Effectively making one piece of mdf that is 2-3 times as thick.

Yes, glued, screwed, and clamped together. I tried to explain that exactly but he continued to tell me that no matter how think it is, it won't get any stronger without bracing. Plus, btw, we are talking about plywood, not MDF.

Obviously he forgot to take a structures class. That being said don't assume that a box with no flex won't be louder than one that does, but you can always expect that a box with minimized flex will color the sound less.

Yeah and that makes sense. Does it make a difference if i said that it wasn't MDF we are talking about but plywood?

I'd rather brace, much less weight, and an unmeasurable amount of loses vs. layering.

Really? That's another point he made about the less weight. What exactly is gained or loss with layering or not layering?

[kirill007 52]

Plywood are layers of 'wood', so it is more effective if you do it with plywood it makes it one thicker piece of plywood.

If u use only 1 ply of the 12 plies(spelling?) in the plywood it should have the same strenght according to him?

It does get stronger if u layer it.

And another reason why to atleast double layer it is that with heavy subs the screws tend to snap out.

So thicker means more "meat" the screw can grip.

EDIT: Normally you can get more strenght if u use a good bracing technique.

Adding layers is less effective then bracing, but the airflow is more obstructed when u use too much bracing.

The key is to find the right amount of layers and bracing

Edited March 14, 2011 by kirill007

[///M5 2,833]

Depends on the goal. Strength is just a very small part. Not having active modal responses in the operating frequency of the driver another. (Modal includes frequency and damping).

[DarkTinman 9]

Plywood are layers of 'wood', so it is more effective if you do it with plywood it makes it one thicker piece of plywood.If u use only 1 ply of the 12 plies(spelling?) in the plywood it should have the same strenght according to him?It does get stronger if u layer it.And another reason why to atleast double layer it is that with heavy subs the screws tend to snap out.So thicker means more "meat" the screw can grip.EDIT: Normally you can get more strenght if u use a good bracing technique.Adding layers is less effective then bracing, but the airflow is more obstructed when u use too much bracing.The key is to find the right amount of layers and bracing

Yeah but at the same time plywood bends pretty easily. I understand the screws and that makes sense. Also, good point about the bracing and the layering. Very solid points. Would it make sense and be possible to do, plywood box on the outside (3/4) then a layer of 3/4 MDF on the inside of the box, then add bracing, and then fiberglass? That's kinda the idea we had for right now, if that makes no sense or if it's stupid let me know asap lol!

P.S. : What exactly happens if there is too much bracing? What happens then?

Depends on the goal. Strength is just a very small part. Not having active modal responses in the operating frequency of the driver another. (Modal includes frequency and damping).

Well, the goal is to be loud obviously and to also have a solid box. I do not want a box that is moving back and forth in my car. I also do not want to lose any airflow to other places other then the port.

[///M5 2,833]

Depends on the goal. Strength is just a very small part. Not having active modal responses in the operating frequency of the driver another. (Modal includes frequency and damping).

Well, the goal is to be loud obviously and to also have a solid box. I do not want a box that is moving back and forth in my car. I also do not want to lose any airflow to other places other then the port.

If you have only one shot at it, I'd brace it and double up.

[DarkTinman 9]

Depends on the goal. Strength is just a very small part. Not having active modal responses in the operating frequency of the driver another. (Modal includes frequency and damping).

Well, the goal is to be loud obviously and to also have a solid box. I do not want a box that is moving back and forth in my car. I also do not want to lose any airflow to other places other then the port.

If you have only one shot at it, I'd brace it and double up.

What do you mean? You saw me talking about my box. Is plywood then a layer of MDF inside and bracing. Then through some fiberglass on top of that. What do you think about it?

[///M5 2,833]

Comment was to overbuild if you aren't going to try multiple boxes. Testing on lots of parameters is required to maximize the loudness.

Fiberglassing resin on top of mdf will weaken it, but will smooth the surface. As long as the rest of the structure is strong enough the amount it weakens it won't matter and could improve your score.

[kirill007 52]

I don't get why you would want to use weaker MDF on the inside?(to cover costs? if that's the case then do it)

If you have the money just use plywood twice and resin+fiberglass on the inside and then smooth everything out.(by sanding)

Offcourse use bracing.

Somthing like this: (although i use a slight different variant)

[DarkTinman 9]

Comment was to overbuild if you aren't going to try multiple boxes. Testing on lots of parameters is required to maximize the loudness.Fiberglassing resin on top of mdf will weaken it, but will smooth the surface. As long as the rest of the structure is strong enough the amount it weakens it won't matter and could improve your score.

No just one box. I saw a lot of people use fiberglass on MDF and i thought that (and told) because the fiberglass resin wasn't exactly water and was more of a "paste" that the MDF doesn't actually get weaker.

I don't get why you would want to use weaker MDF on the inside?(to cover costs? if that's the case then do it)If you have the money just use plywood twice and resin+fiberglass on the inside and then smooth everything out.(by sanding)Offcourse use bracing.Somthing like this: (although i use a slight different variant)

The only reason i wanted to or even thought about it was because people have been at me telling me that MDF is the only good wood to sound deaden and the fact that i didn't use any and my box is super thin got me bashed on. I am not trying to cover costs, i rather do it right the first time and not have to go back in and fix areas where i messed up.

So your saying use another 3/4 plywood and then hadd the fiberglass? That will keep the strength (or add to it) while also deadening? Should i add the new layer of plywood, then brace, then fiberglass?

[///M5 2,833]

Fiberglass penetrates the wood. Tests show that it weakens things. People who want loud use it to smooth the interior surface, not strengthen their box.

If you are using VOID free ply then indeed it is better than MDF. If you aren't using void free then you need to not use ply at all. Around here the big box stores do not carry void free and expect it to be 3-5x the price of mdf depending on what you can buy mdf for locally.

He was saying just double the plywood, but again it was assumed you were using good ply. The crap at home depot is worthless.

[DarkTinman 9]

Fiberglass penetrates the wood. Tests show that it weakens things. People who want loud use it to smooth the interior surface, not strengthen their box.

If you are using VOID free ply then indeed it is better than MDF. If you aren't using void free then you need to not use ply at all. Around here the big box stores do not carry void free and expect it to be 3-5x the price of mdf depending on what you can buy mdf for locally.

He was saying just double the plywood, but again it was assumed you were using good ply. The crap at home depot is worthless.

So fiberglass doesn't help with strength at all?

Yeah honestly i don't think i am using VIOD free plywood. At all. I may be very well be using "crap" plywood at home depot. Because this maybe a HUGE problem, what do you recommend on buying for the inside? To help with bracing and layering? What exactly is the good kind of plywood other then VOID?

[///M5 2,833]

void free actually. If you didn't buy it in small sheets or pay at least $65 for a sheet it definitely is not good plywood. Lining it with MDF would be a great idea.

The point of fiberglass in a box is not for strength. Resin is not a strengthener and even mat is not so great at flat areas. There are ways to use mat and rope to add strength, but you are better off with just wood. That doesn't mean the SPL'heads don't have a reason for glassing the inside of their box, it just isn't for strength but again a strong, rigid box is not always the loudest.

[DarkTinman 9]

Oh okay. Yeah sorry i meant void free. So even though the MDF will be weakened by using the fiberglass you recommend lining the inside with MDF and then using fiberglass? Or are you saying don't use fiberglass and just line the inside with MDF? I honestly wish i knew how much the plywood we bought was or what is was actually. I will ask my build partner and ask him what we got because i know he would know.

So if we did buy a higher quality of plywood, it would be ideal to double layer it and add fiberglass?

[Notorious97200 339]

Fiberglass ? I'm not an expert at all, but I don't feel it necessary. It is a lot of work, and maybe money.

I'm really happy with bracings inside all my boxes.

You can feel the improvments each time you add a brace by knocking the panel. Same way to know where to brace more.

[DarkTinman 9]

Alright, so the verdict is that it's Grade B plywood. Worth double stacking it on the inside or no?

EDIT: And what about fiberglass? Still think it's overkill or no?

Edited March 18, 2011 by DarkTinman

[RAM_Designs 25]

What will your setup consist of? That will determine whether or not you really need to double-up.

[DarkTinman 9]

What will your setup consist of? That will determine whether or not you really need to double-up.

2 SSA prototypes with a power handling of 4,000 RMS pushed by 2 AQX3500's, 270xp DC power alt, and then as of right now one 1800 but soon to be 2-3 3100's XS batteries

[DarkTinman 9]

Sorry for the double post! But!!

I am having some trouble with my port. I was told to watch my port area because that would make a huge difference and help so that there would be no port noise. Now, tomorrow or maybe tonight if i can find the paper, i will give you what i have in terms of room and will let you know what area i have to work with. But i believe the big problem is to keep the length low, i think i only have 12 inches to work with. Not exactly remembering what it was

[///M5 2,833]

Alright, so the verdict is that it's Grade B plywood. Worth double stacking it on the inside or no?

EDIT: And what about fiberglass? Still think it's overkill or no?

Can you just not use it? It is really a bad material for a box. You should switch to just mdf.

[///M5 2,833]

Sorry for the double post! But!!

I am having some trouble with my port. I was told to watch my port area because that would make a huge difference and help so that there would be no port noise. Now, tomorrow or maybe tonight if i can find the paper, i will give you what i have in terms of room and will let you know what area i have to work with. But i believe the big problem is to keep the length low, i think i only have 12 inches to work with. Not exactly remembering what it was

Going to have to bend it. Before doing anything else I'd recommend posting everything you plan to do up here as it seems like there are some issues.