Much appreciated! I'm just happy to finally get to the point of building a complete box with various best practices and compare that to a typical box. I'll continue to investigate new materials and methods, but I think for the moment I've found some really solid methods that are easy and cheap to implement.
I believe that's OK for a dedicated sub.
Particularly if you then stick a 50kg pot plant on it.
I remember noting (last century, when I had multiple turntables) that if you held a platter by the edge it would ring like a gong, but not at all when the rubber mat was laid on it.
On paper, bamboo has the same strength: weight, but better self damping, so in theory it is slightly superior - the finished product could be simpler / lighter because you don't need to add as much damping goo.
In practice, I think the acoustic difference would be too small to care about, particularly on a home HiFi where using lots of heavy goo and bracing is acceptable. In such a build, the appearance and scratch resistance of the skin layer are probably more important than whether or not you can take a kilogram off the build.
Since I have access to not-too-costly bamboo panels, and can pick up premade bamboo objects from Ikea, that's what I have tinkered with. If I had cheap alu (and a background in metal work), that's probably what I'd have used.
IMO bamboo doesn't look less cool - I think it looks about as good as hardwood. The main aesthetic drawback, relative to hardwood, is that there are fewer colour and pattern variants.
This is a bamboo mini speaker made with a found object. Pretty easy build, and is possibly the most normal / commercial looking speaker I've made.
https://i.imgur.com/ZpaY91z.jpg
I've veneered a couple of big boxes with a 5mm layer of this stuff:
Strand Woven - Carbonised - 2440 x 1220 - LETO Bamboo
e.g. the dual 15" LF box in my living room uses a double layer of normal ply with a bamboo skin, for a total wall thickness of about 40mm.
This 5mm bamboo would stiffen the walls of this box roughly as much as using the same weight (~2mm thick) of alu as a skin.
In this application, my guess is that a ply-glue-alu laminate would sound EXACTLY the same as a ply-glue-bamboo laminate. Moving the box 5cm, or fiddling with the EQ would cause a bigger SQ difference.
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I think your study is informative and welcome. I also think you should test baltic birch and mdf in the next phase. I know you're testing Baltic Birch and I didnt catch if MDF was a "high performer" or not. Excuse my sarcastic response, its just that the data of the materials in application is much more intriguing to me
Bracing is everything and sort of makes material a side note if a bracing strategy results in desired performance and is practical. CLD bracing is secondary to matrix bracing in my opinion...if you aren't building the box to be inert you are doing it wrong in my personal view...adding CLD to that equation is icing on the cake.... the way matrix bracing has been presented to me, its an all in one solution and I wonder if CLD is a waste of energy or the last 10% when "the best" bracing philosophy is in play. I went a step further and used what I call TL bracing... based on Bill Fitzmaurice matrix bracing and folded transmission lines.
My point is...bracing style is likely much more important than which material is used when dealing with the common cabinet materials. I guess that may be a study someone here could do in the future.
Its like Im saying whats the point of figuring out which material is least resonate if you are just going to use it wrong anyway..... .......................
I am just one opinion of many
One mechanical property that never seems to enter the equation when it comes to cabinet materials is modulus of elasticity, i.e. stiffness. One material being stiffer than another does usually come up, but to what extent, not so much. Aluminum is about 5x stiffer than bamboo. The stiffest bamboo being around 14.3GPa and aluminum being around 69GPa. Average steel coming in at an incredible 200GPa will put almost any material to shame. Even carbon fiber reinforcements don't exceed the modulus of steel until the more exotic flavors are used.
Stiffness vs damping; they are apparently two different animals. It would be nice to know what that magic balance is and it sounds like bamboo and a variety of other, all very different, strategies are tested and respected. From a raw modulus spec. point of view though, something like the average Magico is way stiffer. 2x stiffer would be a lot, but 5x is way out there, even compared to bamboo, and most materials are not near as stiff even as bamboo. Depending on the wood/mdf/whatever, bamboo is about 10-30 times stiffer than common cab materials. Not trying to argue whether Al sounds good or no. Just throwing in a little perspective on where it stacks up on the modulus pecking order, which is pretty high.
Now that I've set myself up by mentioning a Magico cab being stiffer than the average cab, I'll clarify that obviously all boxes are/can be built differently, overbuilt, underbuilt, etc. Ceteris paribus, two identically constructed enclosures, one Al alloy, one wood, the Al cab will be ~5x stiffer at a minimum, and up to 70x and even higher on the stiffness parameter.
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"Aluminum is about 5x stiffer than bamboo"
But also four times as dense.
...so weight for weight, they are about the same.
Scroll down to the "Stiffness to Weight" stuff in this link.
6061-T6 Aluminum vs. Bamboo Plywood :: MakeItFrom.com
Also, some types (and species) of bamboo are stiffer than others.
Strand woven bamboo ply (which breaks the bamboo down and embeds it in resin, kind of like fiberglass) is stiffer / stronger than regular bamboo ply (which has visible strips of bamboo laminated together - as seen in chopping blocks, Ikea products and so on).
But also four times as dense.
...so weight for weight, they are about the same.
Scroll down to the "Stiffness to Weight" stuff in this link.
6061-T6 Aluminum vs. Bamboo Plywood :: MakeItFrom.com
Also, some types (and species) of bamboo are stiffer than others.
Strand woven bamboo ply (which breaks the bamboo down and embeds it in resin, kind of like fiberglass) is stiffer / stronger than regular bamboo ply (which has visible strips of bamboo laminated together - as seen in chopping blocks, Ikea products and so on).
Where I live, modulus of elasticity is explicitly part of the grading system of structural timber.
"For example F8 timbers have the following properties (from AS 1720.1 Table H2.1):
f 'b = 22 MPa the characteristic bending strength
f 'c = 18 MPa the characteristic compression strength (parallel to the grain)
f 't = 13 MPa the characteristic tensile strength (parallel to the grain) - hardwoods
f 's = 2.2 MPa the characteristic shear strength
E = 9100 MPa the characteristic modulus of elasticity parallel to grain"
Structural grading | WoodSolutions
The F ratings do not scale linearly with the modulus of elasticity - it is more complicated for reasons that make sense to Official Clever People 🙂
Birch ply is typically graded F17.
Premium Birch Plywood | Plyco
Ply made from local hardwoods can be as high as F27.
Armourply Hardwood Plywood
2440 x 1200mm x 4mm F27 Hardwood Plybrace - Bunnings Australia
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True, but that begs the interesting question, at least to my mind. How big a role is geometry actually playing? For example, as you bring in the modulus to weight ratio, aluminum gets knocked down a few pegs, as you point out. But to match a given modulus based on density, i.e. bringing bamboo up to Al, it will necessarily have to be done via a different geometry; so thicker cross section. Or you can do some sort of sandwich construction and keep the weight down but have a stiffer panel. But the same holds true for Al, and those same tricks can be played, again bringing up the stiffness to well over that of the bamboo.
When I hear about problems with an Al cab ringing, My first thought is, well, if the Al plates were thicker it wouldn't ring at a given frequency. I'm still seeing this as more of a geometry/cross section problem rather than an inherent problem with aluminum. The damping issue is a really weird aspect to material properties, but I wonder if it begins to play a more prominent role the more a panel is given way to flexing. Still in terms of stiffness, what you can take to the bank is that Al panels are going to physically flex less than regular cabinet materials. Again, bamboo can definitely be made stiffer, but if the same method used to achieve this were applied to Al, then the Al will win that battle.
I'm not surprised that non Al cabs might sound better. When damping is mentioned I'm starting to think that basically means a given material is more quiet when it's flexing. Aluminum probably complains a little louder under pressure 😀
Edit: To the modulus of the various woods, keep in mind that is MPa. Metals are so far above that they use GPa as the order of magnitude.
Edit, edit: This bending calculator is flippin' epic. The most instructive tool for gleaning the stiffness of various materials in an apples to apples comparison I've ever come across. What gets really wild is seeing how well a hollow cross section holds up against a solid one in terms of stiffness. IIRC, a tube with a cross sectional area of about 3/8 the solid cross section will be about 90% as stiff. The core area of a given beam under load is basically doing nothing. Fascinating stuff-
ENGINEERING.com | Beam Deflection Calculators
When I hear about problems with an Al cab ringing, My first thought is, well, if the Al plates were thicker it wouldn't ring at a given frequency. I'm still seeing this as more of a geometry/cross section problem rather than an inherent problem with aluminum. The damping issue is a really weird aspect to material properties, but I wonder if it begins to play a more prominent role the more a panel is given way to flexing. Still in terms of stiffness, what you can take to the bank is that Al panels are going to physically flex less than regular cabinet materials. Again, bamboo can definitely be made stiffer, but if the same method used to achieve this were applied to Al, then the Al will win that battle.
I'm not surprised that non Al cabs might sound better. When damping is mentioned I'm starting to think that basically means a given material is more quiet when it's flexing. Aluminum probably complains a little louder under pressure 😀
Edit: To the modulus of the various woods, keep in mind that is MPa. Metals are so far above that they use GPa as the order of magnitude.
Edit, edit: This bending calculator is flippin' epic. The most instructive tool for gleaning the stiffness of various materials in an apples to apples comparison I've ever come across. What gets really wild is seeing how well a hollow cross section holds up against a solid one in terms of stiffness. IIRC, a tube with a cross sectional area of about 3/8 the solid cross section will be about 90% as stiff. The core area of a given beam under load is basically doing nothing. Fascinating stuff-
ENGINEERING.com | Beam Deflection Calculators
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I know it is a bad idea but I zm making a small cabinet with thin walls...1 cm from eucalyptus ply... big internal damping but bad stifness....it is tough internaly layered with 5mm vibration absortion panels for washing machine...cheap. it is a frame wood...so some damping as well...BBC style. As the front panel is screwed...the isolation layer can isolate a little....I knowvit s an error but it is cheap and I will try different front baffle variation....
The loss by damping was prefered whilr the little cabinet 45cm x 28 x 32...will sing its own song...
For 1 cm thick Panzerholtz ply from Germany or bamboo would have been far better nut also far more expensive for a casual project....so all is about what you are able to do and spend.
The loss by damping was prefered whilr the little cabinet 45cm x 28 x 32...will sing its own song...
For 1 cm thick Panzerholtz ply from Germany or bamboo would have been far better nut also far more expensive for a casual project....so all is about what you are able to do and spend.
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"When I hear about problems with an Al cab ringing, My first thought is, well, if the Al plates were thicker it wouldn't ring at a given frequency. I'm still seeing this as more of a geometry/cross section problem rather than an inherent problem with aluminum."
This seems correct to me.
The Virtues of Panzerholz : An Investigation into the Acoustical Properties of Aluminum and Panzerholz
Tests like this show that a simple panel of alu will ring very loudly at a handful of frequencies.
Their test of (very expensive) plywood show that it rings very softly at a jillion different frequencies.
...but I think that means almost nothing in practice.
Nobody listens to a rectangular panel of material hanging on a string.
When you hack that alu into a complex shape, stick 5 different thickness of damping goo and bracing on it, and drill multiple holes into it for drivers and cables and bolts, it will have those handful of large resonances transformed into a jillion little ones.
...just like the fancy Panzerholz.
"what you can take to the bank is that Al panels are going to physically flex less than regular cabinet materials"
If you compare an alu speaker shell to a ply shell made with identical dimensions - like 1cm thick walls - then yes.
The 120kg alu box will be stiffer then the 30kg ply box.
However, if you adjust the wall thickness, so that both speaker shells weigh the same, then no. The ply box will be similarly stiff, assuming "regular cabinet materials" that are around 14GPa (rated F17 or higher).
My LF cabinet walls are about 4cm thick. The core is normal ply, the outer layers are stiffer (4mm of F27 ply and 5mm of strand woven bamboo)... so in theory this composite will be slightly stiffer than a 1cm alu wall of the same weight.
Again: not that it really matters. The cabinet was fine before I added the extra layers. This is all overkill.
In practice, heaps of mundane stuff - like moving from one chair to another - has a much bigger effect on the bass / sound quality I get.
After a basic quality level is met, it is probably better to look at everything else - dispersion pattern, EQ, room optimisation and so on, rather than to obsess about whether your cabinet materials are hyper premium enough.
This seems correct to me.
The Virtues of Panzerholz : An Investigation into the Acoustical Properties of Aluminum and Panzerholz
Tests like this show that a simple panel of alu will ring very loudly at a handful of frequencies.
Their test of (very expensive) plywood show that it rings very softly at a jillion different frequencies.
...but I think that means almost nothing in practice.
Nobody listens to a rectangular panel of material hanging on a string.
When you hack that alu into a complex shape, stick 5 different thickness of damping goo and bracing on it, and drill multiple holes into it for drivers and cables and bolts, it will have those handful of large resonances transformed into a jillion little ones.
...just like the fancy Panzerholz.
"what you can take to the bank is that Al panels are going to physically flex less than regular cabinet materials"
If you compare an alu speaker shell to a ply shell made with identical dimensions - like 1cm thick walls - then yes.
The 120kg alu box will be stiffer then the 30kg ply box.
However, if you adjust the wall thickness, so that both speaker shells weigh the same, then no. The ply box will be similarly stiff, assuming "regular cabinet materials" that are around 14GPa (rated F17 or higher).
My LF cabinet walls are about 4cm thick. The core is normal ply, the outer layers are stiffer (4mm of F27 ply and 5mm of strand woven bamboo)... so in theory this composite will be slightly stiffer than a 1cm alu wall of the same weight.
Again: not that it really matters. The cabinet was fine before I added the extra layers. This is all overkill.
In practice, heaps of mundane stuff - like moving from one chair to another - has a much bigger effect on the bass / sound quality I get.
After a basic quality level is met, it is probably better to look at everything else - dispersion pattern, EQ, room optimisation and so on, rather than to obsess about whether your cabinet materials are hyper premium enough.
We seem to be on more or less the same page in terms of the stiffness convo. You have the practical experience and so have a good sense of the stiffness of one iteration vs another. One external application where Al "appears" to be stiffer than steel is high-end bicycles. Often times an Al frame will be lighter and stiffer than a steel frame and Al frames are famously unforgiving. Steel frames are very forgiving on the other hand. But the geometry is the giveaway. Al is considerably less stiff than steel, but being also much lighter, it can be constructed with larger diameter tubing, giving it a geometric advantage. Smaller diameter steel tubes are already very thinly drawn, so to keep the weight down at a larger tube diameter the tube would be so thin as to be unusable.
What you describe is along that similar scenario, only in this case Al is the heavy dog. Using weight as a key metric the two construction techniques definitely start to blur together, at least on stiffness. That's where you switch gears and go with the carbon laminates! Taking an aluminum skinned laminate to the extreme, as light as possible, it should still win out at about at least 50-80% stiffer at the same weight wood laminate, IF I'm thinking about this correctly. I dunno, but it's a fun thought experiment!
What you describe is along that similar scenario, only in this case Al is the heavy dog. Using weight as a key metric the two construction techniques definitely start to blur together, at least on stiffness. That's where you switch gears and go with the carbon laminates! Taking an aluminum skinned laminate to the extreme, as light as possible, it should still win out at about at least 50-80% stiffer at the same weight wood laminate, IF I'm thinking about this correctly. I dunno, but it's a fun thought experiment!
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"You have the practical experience"
Not with alu, and much less experience than many of the hobbyists and builders who post here. I'm just pointing out that you can't simply look at one property (several times as stiff) without considering the others (also several times as heavy).
"Using weight as a key metric the two construction techniques definitely start to blur together, at least on stiffness. That's where you switch gears and go with the carbon laminates!"
And/or make different design decisions. The Boominator is, IMO, a good example. I haven't built one, but I admire the choices and compromises the designer made:
--> it has the woofers mounted on opposed walls. This reduces / cancels vibration, so you don't need as beefy a cabinet.
--> The box depth is scaled so has the backs of the woofers are pressed together. The woofer frames thus brace the box, so you don't need other materials (weight) to do that job.
--> Each build makes choices (battery, neo vs. ferrite magnets) to balance cost against weight.
...so they can be pretty light, without needing any megabuck materials.
Not with alu, and much less experience than many of the hobbyists and builders who post here. I'm just pointing out that you can't simply look at one property (several times as stiff) without considering the others (also several times as heavy).
"Using weight as a key metric the two construction techniques definitely start to blur together, at least on stiffness. That's where you switch gears and go with the carbon laminates!"
And/or make different design decisions. The Boominator is, IMO, a good example. I haven't built one, but I admire the choices and compromises the designer made:
--> it has the woofers mounted on opposed walls. This reduces / cancels vibration, so you don't need as beefy a cabinet.
--> The box depth is scaled so has the backs of the woofers are pressed together. The woofer frames thus brace the box, so you don't need other materials (weight) to do that job.
--> Each build makes choices (battery, neo vs. ferrite magnets) to balance cost against weight.
...so they can be pretty light, without needing any megabuck materials.
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I can certainly test that theory. Now I did test a standard .75" x 1.5" oak brace (see my thread or website), but if you can provide specific guidance I can test that too. My boxes are (externally) 18"x8"x10.5. So a typical standmount speaker for a single 6-7" woofer. What sort of brace would you like me to implement?
I can give you a starting point but to be scientific we must acknowledge that different materials and various thickness of material require different bracing. Lets focus on the popular Matrix bracing which is a construct of crossbeams that reach from wall to wall, spacing and bracing thickness are are variables per material/thickness.
The approach from Bill is this
I use 3/4" ply, so to extrapolate the data ....0.5/.75=1.5(6)=9" so with 3/4" ply, 9" spacing......
This approach of Bills has been developed around Baltic Birch ply.....change the material and thickness, brace spacing changes. From a technical point of view I was told to study Flexural modulus, which I never did. Bill has been around (in the Diy community) for a long time, is an engineer, and is the only person I know of who confidently will say he can make a non resonate cabinet from 1/2 plywood.
I'm not advocating at this point, I am passing on the info sort to speak
Bracing101 2021 - BillFitzmaurice.info
I took this info and did something else with it but I think since this Matrix bracing has a following as well as the fact that there are manufactures using this strategy as well. Its a good starting point.
The approach from Bill is this
I use 3/4" ply, so to extrapolate the data ....0.5/.75=1.5(6)=9" so with 3/4" ply, 9" spacing......
This approach of Bills has been developed around Baltic Birch ply.....change the material and thickness, brace spacing changes. From a technical point of view I was told to study Flexural modulus, which I never did. Bill has been around (in the Diy community) for a long time, is an engineer, and is the only person I know of who confidently will say he can make a non resonate cabinet from 1/2 plywood.
I'm not advocating at this point, I am passing on the info sort to speak
Bracing101 2021 - BillFitzmaurice.info
I took this info and did something else with it but I think since this Matrix bracing has a following as well as the fact that there are manufactures using this strategy as well. Its a good starting point.
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Way overkill unless a bunch of them are going to be stacked/arrayed and/or going to take a beating in transit. With that much bracing you could skin it with 1/4" no void ply in a HIFI/HT app.
There's still the [lack of] mass issue though, so put removable weight on top as required.
There's still the [lack of] mass issue though, so put removable weight on top as required.