brace it with crackers.... for when the hemps give you the munchies 
Seriously, another suitable material could be Alowood, a hardwood vacuum impregnated with some organic agent that replaces the air and moisture in wood, making it very stable and easy to mill. I've toyed with some samples and loved working with it, speaker cabinets quickly came to mind, shame the samples weren't big enough to build a cabinet.
As for MDF VS ply arguments, most have been covered already, I have to add that whenever I build something out of nice ply like baltic birch, the resulting product just feels better. When I use MDF I try to hide it with finishes and keep quiet about the material, although, sonics wise, I have had satisfying results with both.
Seriously, another suitable material could be Alowood, a hardwood vacuum impregnated with some organic agent that replaces the air and moisture in wood, making it very stable and easy to mill. I've toyed with some samples and loved working with it, speaker cabinets quickly came to mind, shame the samples weren't big enough to build a cabinet.
As for MDF VS ply arguments, most have been covered already, I have to add that whenever I build something out of nice ply like baltic birch, the resulting product just feels better. When I use MDF I try to hide it with finishes and keep quiet about the material, although, sonics wise, I have had satisfying results with both.
Hi,
http://www.tms.org/pubs/journals/JOM/9812/Das-9812.html
Dave's post #317, not that far off, we have rapid prototypes and one off's made using Selective Laser Sintering, amongs other tecniques, beauty of it is you can create structures that cant be manufactured in any other way, a good example is a chair with skin walls and internal structure to brace and conrol and applied forces. This method of manufacturing combined with 3D design FEA etc could be used to create the optimum design in from and function.
http://www.tms.org/pubs/journals/JOM/9812/Das-9812.html
Hi,
Organo-metal cabinet structure has already “grown” on planet Earth. Organic resin and 200lb of heavy metal powder has been used for a pair of Lowther horns. Thanks to designed properties of the material, their structure (form) is less complex and more functional than any other BLH I know.
For opponents of heavy material, there is always carbon fiber composite alternative which is already being used to make first class string instruments.
Marek
http://gallery.AudioAsylum.com/cgi/view.mpl?UserImages=21150&invite=
Organo-metal cabinet structure has already “grown” on planet Earth. Organic resin and 200lb of heavy metal powder has been used for a pair of Lowther horns. Thanks to designed properties of the material, their structure (form) is less complex and more functional than any other BLH I know.
For opponents of heavy material, there is always carbon fiber composite alternative which is already being used to make first class string instruments.
Marek
http://gallery.AudioAsylum.com/cgi/view.mpl?UserImages=21150&invite=
Hi Marek, I'd be curious to how the horn was manufactured.
The link below is for the Osteon chair, that shows how a complex internal structure can be 'grown' using modern rapid prototypeing/rapid manufacturing methods.
http://3dvisa.cch.kcl.ac.uk/project28.html
It is also IMO a very good example of minimum wall thicknes / bracing. And of course theres a whole plethora of modern materials that could be investigated.
Of course then in the year 3000 we'll have "Why not Polytetrafluoroethylene" debates, providing none stick to using the same material.
The link below is for the Osteon chair, that shows how a complex internal structure can be 'grown' using modern rapid prototypeing/rapid manufacturing methods.
http://3dvisa.cch.kcl.ac.uk/project28.html
It is also IMO a very good example of minimum wall thicknes / bracing. And of course theres a whole plethora of modern materials that could be investigated.
Of course then in the year 3000 we'll have "Why not Polytetrafluoroethylene" debates, providing none stick to using the same material.
Hi Marce,
It was totally DIY project done at home. First I built a male mold on 4x4’ platform, the mouth and compression chamber facing down.
The mouth section of the mold was made of corrugated cardboard. Cardboard rings were spaced 10 cm apart on a cardboard frame shaped like a horn. Like a frame for a wooden canoe. I covered the cardboard frame with leyers of paper soaked with diluted wood glue, dried it and sealed with poly. I then plastered it to correct the shape, covered it with a thin layer of fiberglass and sanded it to a smooth finish.
I made the compression chamber mold from laminated block of MDF on a lathe. After that a mold of first meter of the horn was made from cardboard circles mounted on rigid copper pipe. The curve part was made the same way, with cardboard circles, but mounted on ½”Cu tube bent to required shape. The circles were covered with rigid aluminum foil, taped with masking tape and plastered to correct the profile.
I covered the form with several layers of fiberglass/metal powder composite. The metal powder was mixed into polyester resin to provide acoustical damping of the material. The first meter and the curved part of the mold had to be broken into pieces to be removed from the finished horn.
It was totally DIY project done at home. First I built a male mold on 4x4’ platform, the mouth and compression chamber facing down.
The mouth section of the mold was made of corrugated cardboard. Cardboard rings were spaced 10 cm apart on a cardboard frame shaped like a horn. Like a frame for a wooden canoe. I covered the cardboard frame with leyers of paper soaked with diluted wood glue, dried it and sealed with poly. I then plastered it to correct the shape, covered it with a thin layer of fiberglass and sanded it to a smooth finish.
I made the compression chamber mold from laminated block of MDF on a lathe. After that a mold of first meter of the horn was made from cardboard circles mounted on rigid copper pipe. The curve part was made the same way, with cardboard circles, but mounted on ½”Cu tube bent to required shape. The circles were covered with rigid aluminum foil, taped with masking tape and plastered to correct the profile.
I covered the form with several layers of fiberglass/metal powder composite. The metal powder was mixed into polyester resin to provide acoustical damping of the material. The first meter and the curved part of the mold had to be broken into pieces to be removed from the finished horn.
"When all you have is a nail, every tool starts to look like a hammer."
I happen to use MDF, for the availability, machinability, and cheapability.
I think my speakers sound fine. I don't have a clue how the SAME speaker
design would sound, using different materials. I've seen many pictures
of speakers made with baltic birch, and like the looks of them, and would
use it were it as readily available, and had I more spending money.
The thing is, if you're getting different results, for the same design,
with different materials, that tells me you need to change the design.
Maybe MDF isn't appropriate to make a PARTICULAR design, maybe a speaker
has to be designed with MDF's capabilities in mind. Or, maybe you (the
listener to the speaker) just have to become accustomed to the particular
coloration given by MDF to a design. There are many trade-offs to be made
in producing a speaker, I think the construction material is just one more
of them.
Tom.
I happen to use MDF, for the availability, machinability, and cheapability.
I think my speakers sound fine. I don't have a clue how the SAME speaker
design would sound, using different materials. I've seen many pictures
of speakers made with baltic birch, and like the looks of them, and would
use it were it as readily available, and had I more spending money
.The thing is, if you're getting different results, for the same design,
with different materials, that tells me you need to change the design.
Maybe MDF isn't appropriate to make a PARTICULAR design, maybe a speaker
has to be designed with MDF's capabilities in mind. Or, maybe you (the
listener to the speaker) just have to become accustomed to the particular
coloration given by MDF to a design. There are many trade-offs to be made
in producing a speaker, I think the construction material is just one more
of them.
Tom.
Dead or Alive...
My take on materials :
Dead: critically damped (or dampened , Dave ). Able to absorb energy or damped w/huge mass. MDF belongs here, unless treated to Totem Acoustics loudspeaker methods (inish the inside and outsides in exactly the same manner). This results in an (for the MDF example) a "non-chuffing" sound (MDF has been proven to allow air to pass through it) from occurring and greatly improves bass performance. I'm sure enclosures made with 1/4" steel plate and treated to Dynamat or similar would be a huge improvement. Stone (glued appropriately and with damping material internally) and concrete (made with concrete "board" or cast and finished on both sides, dampened internally) would be a huge improvement as well. Care with MDF can result in good sounding "dead" enclosures.
Alive: usually under-damped, often multilayer (but not necessarily). Think of musical instrument construction materials. The use of tone woods would be interesting, but perhaps not great. This is one of the reasons "solid" wood loudspeakers are not often suggested. Increased mass helps, but additional dampning materials are required. The non-solid wood option is something like baltic birch plywood, which can be had "voidless", and is made of many thin layers per inch (24-26 usually). Having never worked with "apple plywood", I can't state the pluses or minuses of it, but it has been mentioned in books (Loudspeaker Design Cookbook, IIRC). Baltic birch is very good, and at least outperforms MDF, even if no finish is applied to it. It machines like solid wood and looks good with nothing more than poly on it (multiple layers built up to reduce the "ribbon" effect ), or veneered. I like the "natural" look of the poly'd BB, so only time to apply multi layer is required. An aside: JBL often recommends BB ply for its professional enclosures. They could spec anything, but chose BB ply. There must be a reason, and weight certainly would not be the consideration that they would use.
I do not want to seem to hijack this thread (or any), and this is not intended to fan the flames of the "BB-ply vs MDF" arguments. Only a few facts as I understand them.
A more in-depth discussion must consider the construction, total mass, and dampening characteristic of a particular material. Ultimately an enclosure should have a mass approaching "zero", be self-dampened, be ultra-rigid that requires the thinnest possible material (and thus reduce the energy stored to a minimum) not requiring any bracing. The closed to this is the material that Celestion used in the SL 700 mini-monitors (Stereophile review of SL 700 loudspeakers) , "aerolam". Physical realities and costs limit us "DIY"ers. One thing to consider though: If we spend significant $$$s on drivers, cross-overs (for you multi-driver types), and the rest, why not spend some more on enclosure materials, if not prohibitive. If the cost of something like BB ply, then as a minimum consider treating MDF as Totem does. I also wonder about the possible benefits of a lamination of exterior "Aspenite" using good glue and a vacuum bag.
My take on materials :
Dead: critically damped (or dampened , Dave
). Able to absorb energy or damped w/huge mass. MDF belongs here, unless treated to Totem Acoustics loudspeaker methods (inish the inside and outsides in exactly the same manner). This results in an (for the MDF example) a "non-chuffing" sound (MDF has been proven to allow air to pass through it) from occurring and greatly improves bass performance. I'm sure enclosures made with 1/4" steel plate and treated to Dynamat or similar would be a huge improvement. Stone (glued appropriately and with damping material internally) and concrete (made with concrete "board" or cast and finished on both sides, dampened internally) would be a huge improvement as well. Care with MDF can result in good sounding "dead" enclosures.Alive: usually under-damped, often multilayer (but not necessarily). Think of musical instrument construction materials. The use of tone woods would be interesting, but perhaps not great. This is one of the reasons "solid" wood loudspeakers are not often suggested. Increased mass helps, but additional dampning materials are required. The non-solid wood option is something like baltic birch plywood, which can be had "voidless", and is made of many thin layers per inch (24-26 usually). Having never worked with "apple plywood", I can't state the pluses or minuses of it, but it has been mentioned in books (Loudspeaker Design Cookbook, IIRC). Baltic birch is very good, and at least outperforms MDF, even if no finish is applied to it. It machines like solid wood and looks good with nothing more than poly on it (multiple layers built up to reduce the "ribbon" effect ), or veneered. I like the "natural" look of the poly'd BB, so only time to apply multi layer is required. An aside: JBL often recommends BB ply for its professional enclosures. They could spec anything, but chose BB ply. There must be a reason, and weight certainly would not be the consideration that they would use.
I do not want to seem to hijack this thread (or any), and this is not intended to fan the flames of the "BB-ply vs MDF" arguments. Only a few facts as I understand them.
A more in-depth discussion must consider the construction, total mass, and dampening characteristic of a particular material. Ultimately an enclosure should have a mass approaching "zero", be self-dampened, be ultra-rigid that requires the thinnest possible material (and thus reduce the energy stored to a minimum) not requiring any bracing. The closed to this is the material that Celestion used in the SL 700 mini-monitors (Stereophile review of SL 700 loudspeakers) , "aerolam". Physical realities and costs limit us "DIY"ers. One thing to consider though: If we spend significant $$$s on drivers, cross-overs (for you multi-driver types), and the rest, why not spend some more on enclosure materials, if not prohibitive. If the cost of something like BB ply, then as a minimum consider treating MDF as Totem does. I also wonder about the possible benefits of a lamination of exterior "Aspenite" using good glue and a vacuum bag.
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