curved speaker "boxes"
Further to planet10's comment further upthread, this is the cabinet guy piping in.
I'm not a real woodworker, but I did stay at a Holiday Inn once last year.
One of the (printable) expressions in the millwork trade "CCM"
Curves Cost Money; either in labor and material, or material and labor.
The experiment to which he alluded was an homage to the gorgeous B&W Nautilus speakers. Regardless of your impression of the performance of the various models, the production engineering processes involved in the fabrication and finishing of these enclosures is quite a treat to observe.
My initial attempt was achieved by fabricating a skeletal frame consisting of truncated elipsoid top/bottom plates and several open cross braces of MDF, with solid Douglas fir vertical ribs. Tediously wrapped with 4 layers of rubber ply using spray contact rubbber cement. A final finish laminate or veneer skin has yet to be applied.- this is a work still in progress
"RubberPly" is a generic term we use in house to describe 1/4" thick bending plywood that consists of 2 layers of cheap veneer (luan or similar) sandwiching a thin layer of probably synthetic rubber. The grain directions on the outside skins do not alternate - this makes the material very floppy in the direction parallel to the grain, and stiffer in the perpendicular.
The material is much softer than any conventional ply, particle or MDF board, and I found it difficult to obtain a stiff, low resonance enclosure with reasonable quantities.
My preferred material would be a product known as "Kerf-Core", which is available in 1/2" and 3/4" thick. It consists of a series of thin (1/2"wide) particle board strips, spaced approx 1/8" apart (i.e. kerf wide of conventional table saw blade) and laminated between 2 layers of thick phenolic paper. Once scored on the back side, the material can be curved to fairly small radius ( less than 4") while retaining excellent vertical and horizontal stability. With only a few shaped ribs and carefully machined shallow dadoes, you can very quickly fabricate complex shapes, curved in one direction only of course.
Another great advantage is the material's mass - I'd estimate 2-3 times that of rubber ply - providing greater internal damping and physical stability. The drivers in my MTM rubber ply tower weighed as much as the cabinet, and raised the center of balance so high that sand or similar ballast will be required.
There is a similar product named Timber core that has a luan or similar veneer on one side - it is much stiffer than Kerf core and cannot make the smaller radius than I'd want to achieve, and the grain has been known to open up to an unacceptably rough surface that would telegraph through any finish veneer or plastic laminate.
Further to planet10's comment further upthread, this is the cabinet guy piping in.
I'm not a real woodworker, but I did stay at a Holiday Inn once last year.
One of the (printable) expressions in the millwork trade "CCM"
Curves Cost Money; either in labor and material, or material and labor.
The experiment to which he alluded was an homage to the gorgeous B&W Nautilus speakers. Regardless of your impression of the performance of the various models, the production engineering processes involved in the fabrication and finishing of these enclosures is quite a treat to observe.
My initial attempt was achieved by fabricating a skeletal frame consisting of truncated elipsoid top/bottom plates and several open cross braces of MDF, with solid Douglas fir vertical ribs. Tediously wrapped with 4 layers of rubber ply using spray contact rubbber cement. A final finish laminate or veneer skin has yet to be applied.- this is a work still in progress
"RubberPly" is a generic term we use in house to describe 1/4" thick bending plywood that consists of 2 layers of cheap veneer (luan or similar) sandwiching a thin layer of probably synthetic rubber. The grain directions on the outside skins do not alternate - this makes the material very floppy in the direction parallel to the grain, and stiffer in the perpendicular.
The material is much softer than any conventional ply, particle or MDF board, and I found it difficult to obtain a stiff, low resonance enclosure with reasonable quantities.
My preferred material would be a product known as "Kerf-Core", which is available in 1/2" and 3/4" thick. It consists of a series of thin (1/2"wide) particle board strips, spaced approx 1/8" apart (i.e. kerf wide of conventional table saw blade) and laminated between 2 layers of thick phenolic paper. Once scored on the back side, the material can be curved to fairly small radius ( less than 4") while retaining excellent vertical and horizontal stability. With only a few shaped ribs and carefully machined shallow dadoes, you can very quickly fabricate complex shapes, curved in one direction only of course.
Another great advantage is the material's mass - I'd estimate 2-3 times that of rubber ply - providing greater internal damping and physical stability. The drivers in my MTM rubber ply tower weighed as much as the cabinet, and raised the center of balance so high that sand or similar ballast will be required.
There is a similar product named Timber core that has a luan or similar veneer on one side - it is much stiffer than Kerf core and cannot make the smaller radius than I'd want to achieve, and the grain has been known to open up to an unacceptably rough surface that would telegraph through any finish veneer or plastic laminate.
I am about to start building my speakers, and I too am going for a curved style......
I intend to build up the speaker from ground up in layers, bonded together...imagine a U shape with the top two points joined burned out of 38mm mdf, one on top of other will look a bit like a toilet seat from the top... .will glue in conventional style baffle for drivers...about 22 layers per speaker - 4 sheets of mdf 
luckily I use a laser at work, and can get the mdf in for trade prices....
a different way to attack from?
btw, the mdf will be veneered over for finish....
hth
Rob
I intend to build up the speaker from ground up in layers, bonded together...imagine a U shape with the top two points joined burned out of 38mm mdf, one on top of other will look a bit like a toilet seat from the top...
.will glue in conventional style baffle for drivers...about 22 layers per speaker - 4 sheets of mdf luckily I use a laser at work, and can get the mdf in for trade prices....
a different way to attack from?
btw, the mdf will be veneered over for finish....
hth
Rob
stack'em high
If you're able to machine all the ribs on CNC, include at least 3 registration through holes per layer for continuous wooden dowels. Make the holes slightly larger (.5 - 1mm) than the dowels to ease assembly This will ensure accurate alignment of the parts, requiring less post lamination sanding, and also prevent the individual layers from slipping during clamping.
Dry fit everything together to confirm fit before gluing up.
Use a slow setting 2 part epoxy wood glue ( i.e UF109) and you'd have plenty of time to stack all the parts and clamp up. Leave it clamped up overnight.
You should be able to achieve an enclosure shell without any metal fasteners. This is rather easy to do with biscuits on rectangualr boxes, but takes more thought on curves.
good luck, and post some pictures?
If you're able to machine all the ribs on CNC, include at least 3 registration through holes per layer for continuous wooden dowels. Make the holes slightly larger (.5 - 1mm) than the dowels to ease assembly This will ensure accurate alignment of the parts, requiring less post lamination sanding, and also prevent the individual layers from slipping during clamping.
Dry fit everything together to confirm fit before gluing up.
Use a slow setting 2 part epoxy wood glue ( i.e UF109) and you'd have plenty of time to stack all the parts and clamp up. Leave it clamped up overnight.
You should be able to achieve an enclosure shell without any metal fasteners. This is rather easy to do with biscuits on rectangualr boxes, but takes more thought on curves.
good luck, and post some pictures?
thanx for the advice, chrisb
The only problem with laser cutting is that it isnt a perfect, "square"cut- the edges bow in slightly in the middle , edge to edge looks like this..... ) ( but not sooo bad..
I'm gonna make a jig and spend an afternoon/evening routing across all the edges to flatten, leaving minimal sanding for lamination....
I am looking forwards to taking some pics as and when (am ordering my mdf tomorrow..)
Thanx for the interest!
Rob
btw, i am making the walls 50mm thick - how 'kin heavy are these speakers gonna be? (700 high/600 deep/350 wide)
The only problem with laser cutting is that it isnt a perfect, "square"cut- the edges bow in slightly in the middle , edge to edge looks like this..... ) ( but not sooo bad..
I'm gonna make a jig and spend an afternoon/evening routing across all the edges to flatten, leaving minimal sanding for lamination....
I am looking forwards to taking some pics as and when (am ordering my mdf tomorrow..)
Thanx for the interest!
Rob
btw, i am making the walls 50mm thick - how 'kin heavy are these speakers gonna be?
(700 high/600 deep/350 wide)
RobWells said:thanx for the advice, chrisb
btw, i am making the walls 50mm thick - how 'kin heavy are these speakers gonna be?
is that a new model of Linn loudspeaker for the adult party room B/D dungeon.... the Kinki?
oh, I get it - over here we'd say 'ow effen 'eavy? mate
hard to do the quick math on volume of a truncated elliptical toroidal column (whew!) but I'd say rather!
a rectangular column roughly those dimensions would be about 110lbs - round over those top/bottom edges - depending on quality of tooling, MDF can be machined to a very sharp edge
hi guys.
seems like everyone is now interested in the curved panels.
I am in India so I have to work with limited tools. The way I pla to do this is to build a pattern (sort of like a former) a deep groove in solid wood.
then I intend put the ply (4' x 16") in this groove.I willl need to such fomers(on at the proposed botom of the cabinet and one at the top) to keep the ply level. The grooves in the solid wood will dictate the shape of the curve.
the grooves will be 27mm wide so it will be tight for 3 x 8mm MDF and 2x 1.5mm lead.
the 5 layers will be glues together using expoy cement and then nailed and screwed at 6" intervals.
the panels will have the edges finished in 6 mm thick solid wood so the layers will be be visible and this 6 mm wood wiil prevent the panels edges from opening up. we get this 6mm thick wood in 25mm and 30mm wide strips. Hence the max thickness of teh panels can be 28-29mm (to allow for trimming).
After the side panels are made and in shape the bracing will be added.
the front baffle (10 or 11" wide) will be in 2 or 3 parts. the top part will be about 12" and will hold the 6" and 1". the bottom part will be 36" (I might break this into 12" and 24") and will hold the 8".
Here I am trying to duplicate the cruve of baffle of the Theil CS 3.6. any ideas?
Regards
Navin
seems like everyone is now interested in the curved panels.
I am in India so I have to work with limited tools. The way I pla to do this is to build a pattern (sort of like a former) a deep groove in solid wood.
then I intend put the ply (4' x 16") in this groove.I willl need to such fomers(on at the proposed botom of the cabinet and one at the top) to keep the ply level. The grooves in the solid wood will dictate the shape of the curve.
the grooves will be 27mm wide so it will be tight for 3 x 8mm MDF and 2x 1.5mm lead.
the 5 layers will be glues together using expoy cement and then nailed and screwed at 6" intervals.
the panels will have the edges finished in 6 mm thick solid wood so the layers will be be visible and this 6 mm wood wiil prevent the panels edges from opening up. we get this 6mm thick wood in 25mm and 30mm wide strips. Hence the max thickness of teh panels can be 28-29mm (to allow for trimming).
After the side panels are made and in shape the bracing will be added.
the front baffle (10 or 11" wide) will be in 2 or 3 parts. the top part will be about 12" and will hold the 6" and 1". the bottom part will be 36" (I might break this into 12" and 24") and will hold the 8".
Here I am trying to duplicate the cruve of baffle of the Theil CS 3.6. any ideas?
Regards
Navin
could you not use your bracing as a jig - bolt it to a plank of wood baffle down, and bend your layers around it, using glue and nails to hold it in place while it dries.
If you raised it you could wrap weighted strapping over it to keep an even pressure on while it all sets..
a different angle?
Rob
If you raised it you could wrap weighted strapping over it to keep an even pressure on while it all sets..
a different angle?
Rob
laminating curves
It's very hard to ensure completely uniform pressure on a curved surface using standard clamping techniques. The result, particularly with very springy material, could be voids between layers. At the very least this would affect the cosmetics of the finish, at the worst it could affect the structural integrity of the assembly
If laminating sheet goods rather than "coopered" sticks ( as in barrel-making), some prefered methods would be:
1) Custom formed caul plates, and hydraulic or pneumatic pressure clamps. Once again I'd refer anyone interested in this technique to the printed brochure and website by B&W - the Nautilus series outlines this process very well. The downside is capital investment in shop equipment is a bit steep for the average DIY-er
2) vacuum bag - widely used by boatbuilders and other fabricators of custom shapes in glass or carbon fibre.
The vacuum pump is used to remove all air pressure from the "inside" of the form, allowing atmospheric pressure to to the job.
There is probably information available on the net on how to fabricate your own vacuum bag - a "shop-vac" is not adequate to fully evacuate the pressure from inside the bag - a vacuum pump is mandatory.
It's very hard to ensure completely uniform pressure on a curved surface using standard clamping techniques. The result, particularly with very springy material, could be voids between layers. At the very least this would affect the cosmetics of the finish, at the worst it could affect the structural integrity of the assembly
If laminating sheet goods rather than "coopered" sticks ( as in barrel-making), some prefered methods would be:
1) Custom formed caul plates, and hydraulic or pneumatic pressure clamps. Once again I'd refer anyone interested in this technique to the printed brochure and website by B&W - the Nautilus series outlines this process very well. The downside is capital investment in shop equipment is a bit steep for the average DIY-er
2) vacuum bag - widely used by boatbuilders and other fabricators of custom shapes in glass or carbon fibre.
The vacuum pump is used to remove all air pressure from the "inside" of the form, allowing atmospheric pressure to to the job.
There is probably information available on the net on how to fabricate your own vacuum bag - a "shop-vac" is not adequate to fully evacuate the pressure from inside the bag - a vacuum pump is mandatory.
will try all that meanwhile i ran into another problem. 8mm MDF is damn tough to bend at the relatively sharp bends I am looking for (a la Wilson Benesch Act 2 or Sonus Faber Amati).
tried 6mm and that is tough too so will try 4mm now.
the other question...
if say I get 4mm MDF to work I would need 6 layers of MDF to make 24mm. Is this better than using ply?
question 2.
should I use 2 layers of 1.5mm lead or 1 layer of 3mm lead.
if I use 2 layers of lead I would have 8mm MDF-lead-8mm MDF-lead-8mm MDF
if I use one layer of lead I would ahve 12mm MDF-lead and 12mm MDF or alternaltey 20mm MDF-lead-4mm MDF. 20mm being the inside of the cabinet and 4mm being the skin on which I add veneer etc.
never thought I would get into this kind of trouble before I started this.
Once I start I will make photos. If I do make photos where can I post them? Any audio related site which will allow me to post photos for free?
Regards
Navin
tried 6mm and that is tough too so will try 4mm now.
the other question...
if say I get 4mm MDF to work I would need 6 layers of MDF to make 24mm. Is this better than using ply?
question 2.
should I use 2 layers of 1.5mm lead or 1 layer of 3mm lead.
if I use 2 layers of lead I would have 8mm MDF-lead-8mm MDF-lead-8mm MDF
if I use one layer of lead I would ahve 12mm MDF-lead and 12mm MDF or alternaltey 20mm MDF-lead-4mm MDF. 20mm being the inside of the cabinet and 4mm being the skin on which I add veneer etc.
never thought I would get into this kind of trouble before I started this.
Once I start I will make photos. If I do make photos where can I post them? Any audio related site which will allow me to post photos for free?
Regards
Navin
tried doing what robwells suggested.
the problem wiht using the bracing as a jig is that when i screw the MDF to the bracing as one screws the MDF and the MDF bends the angle at which the screw enters the bracing changes.
tried bending 6mm MDF today. no luck. will have to use 4mm MDF.
I am thinking of using 5 layers of 4mm MDF to make 20mm MDF then using 3mm of lead and a final 4mm MDF as a cover.
any other suggestions? Meanwhile Andy G's and other crossovers are in abeyance.
regards
navin
the problem wiht using the bracing as a jig is that when i screw the MDF to the bracing as one screws the MDF and the MDF bends the angle at which the screw enters the bracing changes.
tried bending 6mm MDF today. no luck. will have to use 4mm MDF.
I am thinking of using 5 layers of 4mm MDF to make 20mm MDF then using 3mm of lead and a final 4mm MDF as a cover.
any other suggestions? Meanwhile Andy G's and other crossovers are in abeyance.
regards
navin
Try to bend the mdf to the jig first (using a friend) then screw straight through it. If I was trying this I'd start in the middle at the back (screwing all the way from top to bottom), and work equally one side then the other....
what about using thin strips, say 3" wide all glued down the joins, then overlapping the joins on the next layer. You could veneer the last layer to make it look nice.....
You could use thicker wood with a loose tongue and groove join - again with copious amounts of glue to fill all the voids....
Hope this helps
Rob
what about using thin strips, say 3" wide all glued down the joins, then overlapping the joins on the next layer. You could veneer the last layer to make it look nice.....
You could use thicker wood with a loose tongue and groove join - again with copious amounts of glue to fill all the voids....
Hope this helps
Rob
well there are 2 ways from the way I see it.
1. use 4mm MDF and use multiple layers (6 in my case). I would then bond 5 layers to make 20mm MDF then add the lead (3mm) and then add the last layer.
2. use 18 or 25mm MDF but break it into vertical strips and use toungue and grove joints. This way the sides will be made of many vertical strips (maybe as many as 6) then cover the strips with lead sheet (3mm, cover that with 4mm MDF and lastly cover that with veneer. I am using teh 4mm MDF as a shield so my son (born April 4th 2002) accidently does not get his hands on the lead as he begins to crawl.
Regards
Navin
1. use 4mm MDF and use multiple layers (6 in my case). I would then bond 5 layers to make 20mm MDF then add the lead (3mm) and then add the last layer.
2. use 18 or 25mm MDF but break it into vertical strips and use toungue and grove joints. This way the sides will be made of many vertical strips (maybe as many as 6) then cover the strips with lead sheet (3mm, cover that with 4mm MDF and lastly cover that with veneer. I am using teh 4mm MDF as a shield so my son (born April 4th 2002) accidently does not get his hands on the lead as he begins to crawl.
Regards
Navin
curved enclosures
The significant factors in determining material and fabrication techniques are the desired shape and radius dimensions. You don't want to be fighting the materials properties.
The photos on the referenced Sonus / Amati page clearly show that the very small radius at rear of enclosure is a block of solid wood (maple I think in this example). The curved sides of enclosure would appear to be a section of very large ellipse, laminated over the horizontal ribs.
3mm MDF is flexible enough to wrap this shape in several layers; any thicker and you'll probably get too much spring-back.
Ideally, you'd like to route very shallow(1mm) dadoes to index to the horizontal rib braces, but this risks breaking the material. Subsequent layers could be glued and clamped as per the photos-no further screws or nails should be required.
This will be a time consuming process; at least 8 layers would be required for nominal 25mm thick walls, with at least overnight curing between layer. But, as I said earlier - CCM- and the result should be very solid and low in resonances
A series of "coopered" vertical slats with angled sides would allow for quicker build up of wall thickness, but has a couple of disadvantages:
- if the curve is not a constant radius, each slat would require calculation and machining of a different set of angles
- although precise machining and adequate clamping could ensure sealing of all joints, and you might only need 1 layer of slats to achieve the desired wall thickness; any labour you potentially save over the layered sheet technique will be lost in time required to cut the slats, and to fair out the flat surfaces to a uniformly smooth curve.
The final finish surface could be plastic laminate, wood veneer or paint on the MDF.
The significant factors in determining material and fabrication techniques are the desired shape and radius dimensions. You don't want to be fighting the materials properties.
The photos on the referenced Sonus / Amati page clearly show that the very small radius at rear of enclosure is a block of solid wood (maple I think in this example). The curved sides of enclosure would appear to be a section of very large ellipse, laminated over the horizontal ribs.
3mm MDF is flexible enough to wrap this shape in several layers; any thicker and you'll probably get too much spring-back.
Ideally, you'd like to route very shallow(1mm) dadoes to index to the horizontal rib braces, but this risks breaking the material. Subsequent layers could be glued and clamped as per the photos-no further screws or nails should be required.
This will be a time consuming process; at least 8 layers would be required for nominal 25mm thick walls, with at least overnight curing between layer. But, as I said earlier - CCM- and the result should be very solid and low in resonances
A series of "coopered" vertical slats with angled sides would allow for quicker build up of wall thickness, but has a couple of disadvantages:
- if the curve is not a constant radius, each slat would require calculation and machining of a different set of angles
- although precise machining and adequate clamping could ensure sealing of all joints, and you might only need 1 layer of slats to achieve the desired wall thickness; any labour you potentially save over the layered sheet technique will be lost in time required to cut the slats, and to fair out the flat surfaces to a uniformly smooth curve.
The final finish surface could be plastic laminate, wood veneer or paint on the MDF.
sorry to interupt, but chrisb - what do you reckon is the "best"minimum thickness of mdf for an enclosure - I was planning on 50mm but am trying to reduce it to increase internal volume. I need 120L and the enclosure is looking to be huge!
The eliptical shape loses a lot of volume compared to a similar "footprinted" rectangular box....
Cheers
Rob
The eliptical shape loses a lot of volume compared to a similar "footprinted" rectangular box....
Cheers
Rob
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