Polyurethane is inherently safe and non-toxic. The panels I just buy, I don't "make" them myself, just cut them up like normal MDF.
The cool thing about poly is that it is infinitely repairable. For example; if I cut the hole in the wrong place, I just glue it back in with polyurethane and it makes the piece just like new. I even make whole panels from scrap. Once complete they are indistinguishable from whole panels.
Now paint! That's another animal altogether, but that's because of the solvents. But casting and cutting don't involve any solvents.
The cool thing about poly is that it is infinitely repairable. For example; if I cut the hole in the wrong place, I just glue it back in with polyurethane and it makes the piece just like new. I even make whole panels from scrap. Once complete they are indistinguishable from whole panels.
Now paint! That's another animal altogether, but that's because of the solvents. But casting and cutting don't involve any solvents.
Ah ok, I thought it was Something injected on a mould or at least some fiber with a glue (like when you make a Kayak for instance) ! Mainly because the horn !
Is it easy to find or did you have to source from the industrial suppliers ?
I don't see why it will be as expensive as some wood ! And in the case it's not ideal for the front bafle, there are all the others sides...
Is it easy to find or did you have to source from the industrial suppliers ?
I don't see why it will be as expensive as some wood ! And in the case it's not ideal for the front bafle, there are all the others sides...
Yes, I cast the waveguides, but otherwise the enclosure is made in the usual way with cut panels and glued joints, but no solid hardware like screws and nails are used. I originally used this material for finishing. The poly can be painted to an amazing finish unlike MDF. MDF is not dimensionally stable and seams always seemed to show. This never happens with the poly - it is impervious to the weather. That's why it is used in many applications.
You can find the stuff all over the place, but not at your local Home Depot. The internet shows lists of suppliers. Renshape is a brand name for the German-made variety. I'm told that there are better US made brands. Renshapes thickness was highly variable. Kind of a PITA.
You can find the stuff all over the place, but not at your local Home Depot. The internet shows lists of suppliers. Renshape is a brand name for the German-made variety. I'm told that there are better US made brands. Renshapes thickness was highly variable. Kind of a PITA.
I have been playing with some exotic finishes using metallic base paint with semi-clear overcoat with a metal flake additive and finally a clear coat. I used this on my latest speakers simulating a paint job that I saw on an Audi RS (something) and it blew me away. It was a totally flat finish over a deep metal flake blue.
For my latest speakers I used a blue metallic base coat with an over-coat in deep purple with metal flakes and then clear coated in a flat clear. The color was simply awesome. I can't understand why people want speakers with wood finishes. They are just so old fashion looking to me. But then this hobby seems to be rather old fashion.
I am going to make my son (Nathan) some Nathans in silver metallic base, over coated in a semi-clear titanium gray with a heavy addition of prismatic metal flakes and then gloss clear coat. I
For my latest speakers I used a blue metallic base coat with an over-coat in deep purple with metal flakes and then clear coated in a flat clear. The color was simply awesome. I can't understand why people want speakers with wood finishes. They are just so old fashion looking to me. But then this hobby seems to be rather old fashion.
I am going to make my son (Nathan) some Nathans in silver metallic base, over coated in a semi-clear titanium gray with a heavy addition of prismatic metal flakes and then gloss clear coat. I
... two stratégies with speakers : make it very visible (Magnepan, Vivid Audio) or the opposite (wood because wood furnitures & parquets) !
My own taste with colors are more towards reniscita fresco colors (smooth and not gloss : it plays differently with te light... saying that, I like also a very deep black gloss like a grand piano Pleyel or even better : natural chineese lacque). Bure tastes & colors ... no scientific answer here !
My own taste with colors are more towards reniscita fresco colors (smooth and not gloss : it plays differently with te light... saying that, I like also a very deep black gloss like a grand piano Pleyel or even better : natural chineese lacque). Bure tastes & colors
... no scientific answer here !which damping materials?
In the 80's I built a pair of speakers from 1/2 inch ply and damped them with a roofing tar/sand mixture. I used a trowel to blend sand into a bucket of roofing tar. My forearms ached for days afterwards. Then I troweled it onto the interior surfaces. It took MONTHS to harden to the point that I could install the drivers and seal the boxes. Never again.
With this in mind, I have a couple of questions. Say I have basic woodworking tools (table saw, router, various sanders, etc.), and the skill to make decent boxes. I don't want to use exotic materials. What strategy would you suggest for boxes in the +/- 2 cubic foot range?
box panels: plywood, MDF, oriented strand board, what?
3/4 inch, 1/2 inch, thinner? thicker?
glues: sounds like a glue that remains somewhat flexible is what is needed. Even ordinary white glue sets up hard. How about something like 3M 4200 or 5200, or Sikaflex, or even ordinary silicone sealant?
damping materials: I can tell you that sand/tar works well for damping. It is also a PITA. Anyone have experience with Quiet Kote damping spray or Acry-Tech coating or similar? Do the damping pads marketed for cars ( one brand name is Sonic Barrier) work for speakers? Roll on truck bedliner? What would you use?
Lastly, I want to say how much I appreciate the contributions to this forum from people with deep knowledge in sound reproduction, professional and serious amateur. Thanks, guys! (and gals?)
In the 80's I built a pair of speakers from 1/2 inch ply and damped them with a roofing tar/sand mixture. I used a trowel to blend sand into a bucket of roofing tar. My forearms ached for days afterwards. Then I troweled it onto the interior surfaces. It took MONTHS to harden to the point that I could install the drivers and seal the boxes. Never again.
With this in mind, I have a couple of questions. Say I have basic woodworking tools (table saw, router, various sanders, etc.), and the skill to make decent boxes. I don't want to use exotic materials. What strategy would you suggest for boxes in the +/- 2 cubic foot range?
box panels: plywood, MDF, oriented strand board, what?
3/4 inch, 1/2 inch, thinner? thicker?
glues: sounds like a glue that remains somewhat flexible is what is needed. Even ordinary white glue sets up hard. How about something like 3M 4200 or 5200, or Sikaflex, or even ordinary silicone sealant?
damping materials: I can tell you that sand/tar works well for damping. It is also a PITA. Anyone have experience with Quiet Kote damping spray or Acry-Tech coating or similar? Do the damping pads marketed for cars ( one brand name is Sonic Barrier) work for speakers? Roll on truck bedliner? What would you use?
Lastly, I want to say how much I appreciate the contributions to this forum from people with deep knowledge in sound reproduction, professional and serious amateur. Thanks, guys! (and gals?)
My 2 cents; 2 cu ft is a decent sized box, so I'd think about 3/4" mdf or good quality plywood like baltic birch. Also 2 cu ft calls for interior bracing. I'd mortise the the joints, and use Titebond II and screws.
I would not use anything wet as a dampening material.
One opinion from the peanut gallery.
I would not use anything wet as a dampening material.
One opinion from the peanut gallery.
One thing to understand is that surface applied damping materials do very little to damp enclosure vibrations. They simply add mass, but essentially no damping. The damping is achieved at the joints and in the structural members like bracing. Cross bracings is by far the most effective place to damp the structure, next would be braces on the panels and the joints - stiffer is not better! Well damped and "stiff enough" is best and yes most white glues dry too hard. There are poly glues that work well, but the best for damping is sand or glass bead filled soft poly. In 2 part it dries in minutes and is viscous enough that mixing in additives is not very hard. It dries to various stiffness's depending on grade.
Eleven ply void free plywood is the best material that is readily available, and not outrageous, that I have found. Custom modeling shops often have it. MDF is good but forget putting on a high grade finish unless you veneer. But its difficult to impossible to veneer a well rounded cabinet, so MDF is out for me. Highly rigid squared off boxes like I mostly see are not the way to go.
Eleven ply void free plywood is the best material that is readily available, and not outrageous, that I have found. Custom modeling shops often have it. MDF is good but forget putting on a high grade finish unless you veneer. But its difficult to impossible to veneer a well rounded cabinet, so MDF is out for me. Highly rigid squared off boxes like I mostly see are not the way to go.
Good talk here.
Planning some cabinets with 1/2" BB ply, and it is 11 Ply. I'll Examine 1/2" inner panels adhered through front to inside walls of BB cabinet, basically box within a box. Now I'm thinking about how the joints should be glued together.
I've been spraying Zinsser Bin Primer Sealer over MDF and it is excellent, a great finish can be applied thereafter. Birch ply is to porous and I need to apply maple veneer before primer/paint and this is why I'm going to try a softwood ply that has 1/8" MDF layer on both sides.
Planning some cabinets with 1/2" BB ply, and it is 11 Ply. I'll Examine 1/2" inner panels adhered through front to inside walls of BB cabinet, basically box within a box. Now I'm thinking about how the joints should be glued together.
I've been spraying Zinsser Bin Primer Sealer over MDF and it is excellent, a great finish can be applied thereafter. Birch ply is to porous and I need to apply maple veneer before primer/paint and this is why I'm going to try a softwood ply that has 1/8" MDF layer on both sides.
Earl, you wrote this : The poly can be painted to an amazing finish unlike MDF. MDF is not dimensionally stable and seams always seemed to show. This never happens with the poly - it is impervious to the weather. That's why it is used in many applications.
Does that men you can simply butt joint the poly pieces, and fill and sand, and no joints will be visable through the paint, also not over time?
Do you also glue the outer poly joints (corners and outher edges on box) with the viscous glue?
Can you saw and route the poly material like MDF? maybe with other blades router bits?
Does that men you can simply butt joint the poly pieces, and fill and sand, and no joints will be visable through the paint, also not over time?
Do you also glue the outer poly joints (corners and outher edges on box) with the viscous glue?
Can you saw and route the poly material like MDF? maybe with other blades router bits?
Firstly, it goes well with other furniture and secondly, a natural looking finish beauty is of the greater order in itself, wood not being a man made product. It is probably written in our genes to appreciate wood for our existence is connected with it.
If I were to build the same, I'd choose the simplest way which would be plywood 3/4", reasonably braced. You get the finish and box at once. I know from experience that board material is not an issue, at least in the conditions of my experiments, a normal home listening environment, not too loud, just about right that you don't get ear ringing afterwards. I have never experienced any sounds one would usually connect with bad enclosure construction. All the bad sounds come from wrong driver implementation, wrong box type, bad XO filter, not treating the air resonances inside box.
Is there some assembly technics better than other ?
45° edge or not ?
Better glues than others ?
Screws + glue ?
forms of internals bracing better than others ?
Is there some dimensions ratios better than others for the internal modes and difractions (the worst ennemy)?
I assume there are no perfect material, but one should have to look at Young module of materials, no ? Best rigidity / internal damping ratio ?!
But best bet is to work on the internal diffraction, with the best size in relation to the Frequency range of the driver... is there any soft to calculate that ? How to do for taming the strongest wave length (the lowest Fhz the driver can reproduce) and all the mods which play with the rear cone surface ?
Being not knowing how to do I would choose the simpliest trade off, whatever the final choosed material !
Now there are some speakers with not so rigid and heavy pannels which sounds good and is a choice of the designer : for i,stance the OB Living Voice !
Some others say than the genuine Altec A5 has not too thick wall for this lively sound (wanted ?), some others prefer make it dead as a stone with doubling with Nantex, Panzerholt wood ! But I'm asking myself if here the weight is not the most factor of the result ? Maybe a chipboard pannel has more internal damping than a PanzerHoltz pannel : but for sure you don't need vibrations from your external pannels to avoid it singing (weight + rigidity wanted I assume with big cone and long exursions!)
45° edge or not ?
Better glues than others ?
Screws + glue ?
forms of internals bracing better than others ?
Is there some dimensions ratios better than others for the internal modes and difractions (the worst ennemy)?
I assume there are no perfect material, but one should have to look at Young module of materials, no ? Best rigidity / internal damping ratio ?!
But best bet is to work on the internal diffraction, with the best size in relation to the Frequency range of the driver... is there any soft to calculate that ? How to do for taming the strongest wave length (the lowest Fhz the driver can reproduce) and all the mods which play with the rear cone surface ?
Being not knowing how to do I would choose the simpliest trade off, whatever the final choosed material !
Now there are some speakers with not so rigid and heavy pannels which sounds good and is a choice of the designer : for i,stance the OB Living Voice !
Some others say than the genuine Altec A5 has not too thick wall for this lively sound (wanted ?), some others prefer make it dead as a stone with doubling with Nantex, Panzerholt wood ! But I'm asking myself if here the weight is not the most factor of the result ? Maybe a chipboard pannel has more internal damping than a PanzerHoltz pannel : but for sure you don't need vibrations from your external pannels to avoid it singing (weight + rigidity wanted I assume with big cone and long exursions!)
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I've done that as well, but over time the seams still show, the material is still hydroscopic and expands and contracts with the weather.
You could but join the poly, but I still miter. No joints have ever shown with poly, no matter where in the world they go. With MDF some joints would show after several months if the speakers went to humid areas. The soft poly is used mostly for CLD and cross bracing where damped flexibility is desired. I use regular poly, which is still well damped, but more rigid for the joints. Since the poly boards are the same material as the glue, the joints when complete become a continuous piece of the same material and will never show.
The poly that I use is a little softer than MDF and cuts easier, but creates a much cleaner cut than MDF (which is always a little ragged.) Poly boards are meant to be machined, that's what they are made for and they do that very well.
Cabinet diffraction is major concern and must be minimized.
Glues are mostly the same, but if the material properties of the glue are the same as the panels then the seams will be better and won't show with time.
I don't like screws.
There are definitely better and worse ways to do internal bracing. It takes some knowledge of structures to do this well.
Internal dimensions are mostly irrelevant as long as redundancy is avoided. A cube is bad, but any box with un equal dimensions will be about the same.
To me the best material is one with the highest stiffness to weight ratio. Poly boards are great in this regard, MDF is medium, most metals are not so good. Carbon fiber would be ideal!! Remember that stiffness goes up as the square of the thickness while weight goes up linearly, so I can get any stiffness that I want with panel thickness, but the heavier material will still have the lower resonance frequencies due to its mass (higher is better.)
Learning something new every day.
Thank you, Dr. Geddes!
"One thing to understand is that surface applied damping materials do very little to damp enclosure vibrations."
I could have built speakers for another 35 years and not stumbled onto this on my own. This is why I appreciate this (and other ) forums and the people who freely share their knowledge. I am going to track down some 2 part poly and start experimenting.
Got time for another question? Should I fit the panels and braces "loose" so to have a thicker layer of glue between them? (assuming regular sheet panel materials like plywood)
Thank you, Dr. Geddes!
"One thing to understand is that surface applied damping materials do very little to damp enclosure vibrations."
I could have built speakers for another 35 years and not stumbled onto this on my own. This is why I appreciate this (and other ) forums and the people who freely share their knowledge. I am going to track down some 2 part poly and start experimenting.
Got time for another question? Should I fit the panels and braces "loose" so to have a thicker layer of glue between them? (assuming regular sheet panel materials like plywood)
Surface damping has worked in experiments done by these people under those circumstances.
Factors in the design of loudspeaker cabinets - BBC R&D
Factors in the design of loudspeaker cabinets - BBC R&D
The panels should be reasonably solidly held together, but not "rigid" per se. But the bracing as added cross braces or on panel braces should be an order of magnitude less stiff than the panel corners. Basically a tight shell is a good idea, but internally the braces should be looser and very well damped.
Surface damping is insignificant when compared to CLD using the same materials, thickness, etc. for structural vibrations. CLD will do nothing for internal sound resonances while the additive will. It's all about getting the most for the least. A paper from KEF clearly shows that a damped cross brace is far more effective than panel damping.