Triticum Agricolam Posted September 21, 2016 Report Share Posted September 21, 2016 I see people asking all the time (sometimes here and a ton on facebook) "what's the best box material?". The two top choices are usually MDF or "birch" which each having its own group of advocates. I thought it would be useful to put some numbers to the debate and help everyone make more informed decisions. The question: The purpose of my experiment is to measure and compare the relative stiffness between materials. I have five materials I will be testing, all are considered to be 3/4" thick. They are as follows: MDF - measured 3/4" thick - everyone knows what this is baltic birch plywood - measured 11/16" thick - the gold standard of enclosure materials (IMHO) it has 13 even thickness plies, its expensive Arauco plywood - measured 23/32" thick - its made from South American Radiata pine and has 7 even thickness plies, this stuff is middle of the road in terms of cost Chinese "pine" plywood - measured 11/16" thick - they claim its pine, it looks a LOT like the usual cheap birch you get at box stores, this has 13 plies with some paper thin face veneers, its cheap OSB - measured 13/16" thick - oriented strand board, super cheap, super ugly Here is my testing apparatus, starting off with the Chinese pine: And here it is with the weight applied: Each board was cut to 3" wide at is at least 22" long. The supports holding the board up are 18" apart. I'm using a 25 lbs. bag of lead shot for weight and the apparatus just makes sure the weight gets applied to one point consistently between the samples. I'm using a dial indicator to measure board deflection in one-thousandths of an inch. The results: MDF - .067" of deflection Chinese Pine - .0415" of deflection - 62% of MDF Baltic Birch - .0315" of deflection - 47% of MDF Arauco Ply - .041" of deflection - 62% of MDF OSB - .023" of deflection - 34% of MDF Conclusion: The MDF is by far the least stiff material, which isn't very surprising, though it is certainly interesting to see just how much less stiff it is. Both the Chinese plywood and the Arauco performed significantly better than MDF and were almost identical to each other. The Baltic Birch was the stiffest of the plywoods, which is also what I expected. What I found really shocking was how stiff the OSB was. I know its intended as a plywood alternative, but its so cheap I didn't think it would perform THAT much better than the other plywoods did. The OSB does have a bit of an unfair advantage though being the thickest of the materials. Its 1/8" thicker than the BB and Chinese plywoods, which is pretty significant. Here is a picture showing the difference: Hopefully this experiment will help people make more informed decisions about what materials to use. My goal here was not to prove the baltic birch plywood (or any other plywood) is the "best" material or than MDF is junk. There are plenty examples of all the different materials being used effectively. Also, there are a lot of factors that go into determining what the best material for a particular job will be and stiffness is just one of those factors, though I do consider it a pretty important one. Things like cost, surface finish, water resistance, ease of use, and weight all need to be considered as well. Something else this experiment has given us to consider is how different materials should be implemented differently during design and construction. I would definitely approach how I was going to brace an enclosure made from MDF differently than I would one made from Baltic Birch. Since the BB plywood is significantly stiffer you could almost certainly get away with less intensive bracing. I'm working on another experiment right now comparing some different bracing strategies, I'll be posting it in the next day or two. ETA: I just posted my thread on bracing, here it is: http://www.stevemeadedesigns.com/board/topic/206664-implementing-bracing/ "Nothing prevents people from knowing the truth more than the belief they already know it.""Making bass is easy, making music is the hard part."Builds: Link to comment Share on other sites More sharing options...
deathcards Posted September 21, 2016 Report Share Posted September 21, 2016 you should weigh the boards just to see the difference Sweet test though skar sk2500.1 0 gauge power and ground kunukonceptz alpine HUvxi65 components on BA gt-275new build log -> http://www.stevemeadedesigns.com/board/topic/150642-project-d-kon-deathcards-build-log/#entry2148821 2 x-15 sundowns singer alt, odyssey bat, and maxwell ultra caps Link to comment Share on other sites More sharing options...
Skullz Posted September 22, 2016 Report Share Posted September 22, 2016 Even though OSB is only 1/16" thicker it has it's strands in every direction compared to plywood which is in a north/south and east/west configuration, and why it is used as a substrate for floors. MDF has no strands of fiber running in any direction which is why the panel deflects as much as it does, but allows it to have a much greater density than the rest of the materials. 01 Ford focus ZX3 Pioneer AVH-X491BHS PPI PC 4800.2 Morel Maximo 6.5" x2 Link to comment Share on other sites More sharing options...
Triticum Agricolam Posted September 22, 2016 Author Report Share Posted September 22, 2016 you should weigh the boards just to see the difference Sweet test though I have the weights written down. I'll post them later. The MDF is the heaviest and I think the arauco is the lightest. "Nothing prevents people from knowing the truth more than the belief they already know it.""Making bass is easy, making music is the hard part."Builds: Link to comment Share on other sites More sharing options...
bsneon98 Posted September 22, 2016 Report Share Posted September 22, 2016 thank you for this man. when i just re did my whole trunk with baltic birch rather than mdf its a ton lighter and stronger,It was hard to figure out just how much but it was significant. Build Log: http://www.stevemeadedesigns.com/board/topic/152954-1998-plymouth-neon-updates/ Link to comment Share on other sites More sharing options...
Triticum Agricolam Posted September 22, 2016 Author Report Share Posted September 22, 2016 you should weigh the boards just to see the difference Sweet test though Here are the weights: Baltic Birch - 2.36 lbs/square foot Arauco - 1.875 lbs/square foot China Pine - 2.06 lbs/square foot MDF - 2.92 lbs/square foot OSB - 2.48 lbs/square foot The high weight of MDF is one of the reasons I don't use it much any more. "Nothing prevents people from knowing the truth more than the belief they already know it.""Making bass is easy, making music is the hard part."Builds: Link to comment Share on other sites More sharing options...
DLHgn Posted September 22, 2016 Report Share Posted September 22, 2016 I'm not sure what I want to use for my next build. I would like to use BB but I don't think I'm confident enough in my wood working skills to ensure I don't mess up a cut and waste wood considering that stuff is fairly expensive. Link to comment Share on other sites More sharing options...
audiofanaticz Posted September 22, 2016 Report Share Posted September 22, 2016 There is more then just how much a piece flexes that goes into it. I would love to use nothing but Baltic, but the reality is not everyone is willing to pay that additional price tag for the material Link to comment Share on other sites More sharing options...
Krakin Posted September 22, 2016 Report Share Posted September 22, 2016 Isn't the whole point of using MDF is because it has enough deflection to be essentially an acoustically dead material? Krakin's Home Dipole Project http://www.stevemeadedesigns.com/board/topic/186153-krakins-dipole-project-new-reciever-in-rockford-science/#entry2772370 Krakin, are you some sort of mad scientist? I would have replied earlier, but I was measuring the output of my amp with a yardstick . . . What you hear is not the air pressure variation in itself but what has drawn your attention in the two streams of superimposed air pressure variations at your eardrums An acoustic event has dimensions of Time, Tone, Loudness and Space Everyone learns to render the 3-dimensional localization of sound based on the individual shape of their ears, thus no formula can achieve a definite effect for every listener. Link to comment Share on other sites More sharing options...
Triticum Agricolam Posted September 22, 2016 Author Report Share Posted September 22, 2016 Isn't the whole point of using MDF is because it has enough deflection to be essentially an acoustically dead material? I think the main reason MDF get used is because "that's what other people do" and because its cheap, at least when it comes to vehicle subwoofer boxes. For full range enclosures I know MDF is really well like because its well damped and "acoustically dead" like you said, but I'm not sure it gets that attribute because it deflects easily. This is outside my area of expertise. "Nothing prevents people from knowing the truth more than the belief they already know it.""Making bass is easy, making music is the hard part."Builds: Link to comment Share on other sites More sharing options...
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