owen said:For small mini-monitors and the like, you could use FR4 PCB as the external cladding (copper side out of course). Very 'stiff', highly damped and less than straight copper on price (wouldnt be cheap though)
Owen
For me, the 22ga. copper is essentially free.
As a side note, aluminum flashing is really, really cheap, and would work just fine - about $7 for about five meters, I think.
I think that using really thin sheet metal will not yield good results for a large cabinet but if bonded properly would be stiff enough for a small speaker as long as internal bracing is used.
It really depends on what sound quality you are shooting for. I think when it comes down to it panel dampening is important but not as important as panel stiffness.
If you have access to the tooling to put strengthening ribs into the sheets that would help a lot. You could make and inner and outershell and glue and rivet the joints together then fill the cavity with what ever grade of expanding foam that you want to buy. The more dense the better.
It really depends on what sound quality you are shooting for. I think when it comes down to it panel dampening is important but not as important as panel stiffness.
If you have access to the tooling to put strengthening ribs into the sheets that would help a lot. You could make and inner and outershell and glue and rivet the joints together then fill the cavity with what ever grade of expanding foam that you want to buy. The more dense the better.
454Casull said:
Styrofoam is just a brand name from Dow Chemicals. It means polystyrene.
Spasticteapot said:
You have those two backwards. Expanded bead is the "popcorn" stuff. It's usually white. It comes as type 1 or type 2 EBPS.
Extruded is often referred to as Styrofoam SM or Roofmate. It is known as Type 4 EPS and commonly comes in blue or pink depending on the manufacturer.
Hezz said:
Polyisocyanurate is another type of rigid board like type 4. It is less expensive than type 4, has a facer and has a lower thermal transfer rate. It is also much less heat sensitive than type 4. Styrofoam roofmate has an R value of 5 per inch and polyiso is around 7 depending on the manufacturer.
Hope that clears thing up.
Forgot to mention, I don't think it is well suited to making a non-resonant box and has been stated, you will have to weigh it down so the woofer doesn't move it around. It also seems like more work than a regular box. Perhaps more expensive also, depending on your finish. What are you planning for a baffle?
Cal Weldon said:
Both aluminum and foam are dead cheap - aluminum flashing is about seven bucks a roll, and foam sheet is a fraction of the cost of plywood.
panomaniac said:
I hope so!
I might use fiberglass on the inside instead. I doubt I would be able to make it look good - but, hey, who cares if it's on the inside?
Young's modulus for Polystyrene is about 3 GPa, whereas MDF's is in the neighborhood of 9-12 GPa. This means that for a given thickness, MDF will move 1/3rd as much a polystyrene. This can be altered somewhat with a far stiffer skin, but most things are dense enough that careful tradeoffs are necessary.
Fortunately, stiffness goes up as a cube of the thickness, so something that's twice as thick will be eight times as stiff. If you make your foam more than two inches thick, you should have a fairly rigid cabinet. If you can rigidly bond something that's light and stiff, like fiberglass, then thinner walls can also be quite stiff.
Local forces from the driver's reaction forces aren't so compatible with this, so you're best off having at least the front baffle made out of wood or solid aluminum.
Fortunately, stiffness goes up as a cube of the thickness, so something that's twice as thick will be eight times as stiff. If you make your foam more than two inches thick, you should have a fairly rigid cabinet. If you can rigidly bond something that's light and stiff, like fiberglass, then thinner walls can also be quite stiff.
Local forces from the driver's reaction forces aren't so compatible with this, so you're best off having at least the front baffle made out of wood or solid aluminum.
Just a quick remark regardless of the foam...
Copper and brass will quickly oxidize and no longer look so pretty. If you do go through with it, spray some clear acrylic or other sealant on the cabinet. Aluminum can be anodized.
Also, I'm not sure what you mean when you say copper is easier to work with than aluminum. My experience machining copper is that is is much more likely to burr and has to be worked with at much slower cutting speeds than aluminum.
-Wes
Copper and brass will quickly oxidize and no longer look so pretty. If you do go through with it, spray some clear acrylic or other sealant on the cabinet. Aluminum can be anodized.
Also, I'm not sure what you mean when you say copper is easier to work with than aluminum. My experience machining copper is that is is much more likely to burr and has to be worked with at much slower cutting speeds than aluminum.
-Wes
I can relate to Spasticteapot's lack of confidence with timber and MDF.
But then you have to bite the bullet. It's not that hard to work with. Just take your time. Measure 18 times and cut once.
Just today I cleaned up / bevelled / rounded off some cut-outs with a spokeshave bought from the flea market. Similar to scraping a bearing to size.
Alternate materials are great if there is a need for them. If metal sandwiches were suitable / economical I think the manufacturers would have gone that way a long time ago.
Instead some are going to plastic injection moulding.
One of the biggest problems with composite laminates is de-lamination, caused by temperature changes and vibration.
Sonically, I can't be certain. Gut feeling says "no" Gut's been wrong before.
Geoff.
But then you have to bite the bullet. It's not that hard to work with. Just take your time. Measure 18 times and cut once.
Just today I cleaned up / bevelled / rounded off some cut-outs with a spokeshave bought from the flea market. Similar to scraping a bearing to size.
Alternate materials are great if there is a need for them. If metal sandwiches were suitable / economical I think the manufacturers would have gone that way a long time ago.
Instead some are going to plastic injection moulding.
One of the biggest problems with composite laminates is de-lamination, caused by temperature changes and vibration.
Sonically, I can't be certain. Gut feeling says "no" Gut's been wrong before.
Geoff.
OK. Ask anyone who has built their own amps what the biggest problem they face. They will probably say the chassis. I used to buy the blank, and drill, cut, and ream. I haven't seen blank chassis for yonks. It may be different in the States.
Tube amps are not rocket science. You could prepare kits ready for final assembly. IE 12x12x2" with 3 transformers, 4 or 5 octal sockets and a couple of 7or 9 pin sockets, waiting for smaller components and soldering iron.
Treated copper looks great reflecting glowing filaments.
Copper may be suitable for horns. Picture one of those multi-cellular units by Western Electric or Altec Lansing. Have a look at what 511s fetch on eBay for example.
Just my 2c.
Geoff
Tube amps are not rocket science. You could prepare kits ready for final assembly. IE 12x12x2" with 3 transformers, 4 or 5 octal sockets and a couple of 7or 9 pin sockets, waiting for smaller components and soldering iron.
Treated copper looks great reflecting glowing filaments.
Copper may be suitable for horns. Picture one of those multi-cellular units by Western Electric or Altec Lansing. Have a look at what 511s fetch on eBay for example.
Just my 2c.
Geoff
The expanding glues like Gorrilla glue are godsends for first time wood builders. They will fill any flaws in your joints without high clamping forces so long as everything is held tightly in place while drying.
Then a little epoxy, bondo and paint can fix and cover any small flaws. Plus MDF is cheap and in the long run the best value for speaker building. Other advance techniques can yield good results but for a lot more work.
Then a little epoxy, bondo and paint can fix and cover any small flaws. Plus MDF is cheap and in the long run the best value for speaker building. Other advance techniques can yield good results but for a lot more work.
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