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My Brother-in-Law wanted a pair of speakers that could be placed close to the wall for the tiime being, but perhaps have a different location when he moves so that they are more conventionally placed. After a search of the DIY published builds, it looked like the Finalists fit the bill admirably.
I am a hobbyist woodworker with no crossover skills but I follow this forum frequently just to admire the work of Curt, Jon and others. I have built a few speakers with designs by Dennis Murphy, Troels Gravesen and Jeff Bagby. So this thread will be only about construction techniques that I use and mostly of interest to those new to speaker building in general and the Finalists in particular. I will try to also augment Curt's build manual with some tips for new builders.
The wrinkles--I'm going to use mitred joints with biscuits on all panels except the front inner baffle and the outer baffle will be solid hardwood. So I will be pointing out the pitfalls and some of the ways to overcome the tendency of hardwood to move with humidity changes and therefore open up splits, bow away from the cabinet or possibly torque a driver frame out of shape. I am not reccommending that hardwood be used generallly for baffles but when I saw Jim Salk's (www.salksound.com) early cabinets I shamelessly copied his style. As an example, my Avatar has solid cherry front baffles. I have been lucky to have avoided splits so far and I do like the look.
My Brother-in-Law wanted dark stained oak to match his furniture, so I purchased the veneer and I already had a 1.5" thick oak plank for the baffles. The oak has been kiln dried and in my house for a few years so it is climatized as much as possible to this environment, It has been cut and glued up for 2 baffles about 26" x 11.25". These are .75" thick and although Jim Holtz calls for just a .5" thick outer baffle, this won't matter as the volume of the box doesn't change. But I may reduce them to the .5" size called for in the design.
To use hardwood baffles, wood expansion has to be minimized. Wood is like a sponge--it takes on moisture from the air and when it does, unlike a sponge, it expands (or contracts when it dries out in winter), which some call wood movement. red oak can shrink and expand up to .325" in 12" in my climate, Southern Ontario, Canada. We have hot humid summers and dry cold winters. On the Finalist front baffle oak could move that quarter inch because it is 11" wide. This would be too much if the mid and woofer frames are let in flush with the baffle surface and fit tight. So oak is not the most stable wood to use. What can be done?
The rate of shrinkage/expansion noted above occurs tangentially to the centre of the tree. Those grain lines that we normally see in wood planks, parabolic in form, normally called cathedral grain are tangential. If we cut a plank and see the cathedral grain, look at the end cut. You will see long arcs moving in the long dimension of the rectangle of the end cut. This is what we don't want. This shrinkage will be the worst case. My plank was like this, so it was sawn in .75" wide strips and the resulting 1.5" strips were turned 90 degress and glued up into the baffles.
Here the end grain is oriented vertically, unlike the cathedral or flat sawn end grain which has horizontal arcs. The largest expansion will occur from the back of the baffle to the front surface. Radial expansion from the centre of the tree to the bark is less than half of the tangential grain--.125" per foot. this is the amount the baffle will stretch from side to side.
The grain on surface of the baffle will look like straight lines, not cathedral parabolas. This is also termed quarter sawn lumber. Quarter sawn lumber will also exhibit grain patterns which look like worms sometimes crossing the straight grain lines. These rays are visible here and were popularized in the Stickley furniture of the early 20th century in the US. They will remain light in colour when the stain is applied. Quarter sawn lumber is not normally seen in HD or Loews. Those who live in the Carolinian forest can find it reasonably easily from a local sawmill or lumber merchant. They will ship anywhere as well but you don't get to pick it unfortunately.
This makes the shrinkage move radially to the heart of the tree and it reduces it to .125" per foot. Still not ideal, but I wanted to try oak for the first time in this application. The wood does not move appreciably on the length of the baffle, about 1/100" per foot. Later in the build, when the baffles are milled for the drivers and attachment to the cabinet, some techniques to prevent the baffle from bowing or splitting will be discussed.
Next post will be about the cabinet cutout and joint construction.
Cheers, Fred
I am a hobbyist woodworker with no crossover skills but I follow this forum frequently just to admire the work of Curt, Jon and others. I have built a few speakers with designs by Dennis Murphy, Troels Gravesen and Jeff Bagby. So this thread will be only about construction techniques that I use and mostly of interest to those new to speaker building in general and the Finalists in particular. I will try to also augment Curt's build manual with some tips for new builders.
The wrinkles--I'm going to use mitred joints with biscuits on all panels except the front inner baffle and the outer baffle will be solid hardwood. So I will be pointing out the pitfalls and some of the ways to overcome the tendency of hardwood to move with humidity changes and therefore open up splits, bow away from the cabinet or possibly torque a driver frame out of shape. I am not reccommending that hardwood be used generallly for baffles but when I saw Jim Salk's (www.salksound.com) early cabinets I shamelessly copied his style. As an example, my Avatar has solid cherry front baffles. I have been lucky to have avoided splits so far and I do like the look.
My Brother-in-Law wanted dark stained oak to match his furniture, so I purchased the veneer and I already had a 1.5" thick oak plank for the baffles. The oak has been kiln dried and in my house for a few years so it is climatized as much as possible to this environment, It has been cut and glued up for 2 baffles about 26" x 11.25". These are .75" thick and although Jim Holtz calls for just a .5" thick outer baffle, this won't matter as the volume of the box doesn't change. But I may reduce them to the .5" size called for in the design.
To use hardwood baffles, wood expansion has to be minimized. Wood is like a sponge--it takes on moisture from the air and when it does, unlike a sponge, it expands (or contracts when it dries out in winter), which some call wood movement. red oak can shrink and expand up to .325" in 12" in my climate, Southern Ontario, Canada. We have hot humid summers and dry cold winters. On the Finalist front baffle oak could move that quarter inch because it is 11" wide. This would be too much if the mid and woofer frames are let in flush with the baffle surface and fit tight. So oak is not the most stable wood to use. What can be done?
The rate of shrinkage/expansion noted above occurs tangentially to the centre of the tree. Those grain lines that we normally see in wood planks, parabolic in form, normally called cathedral grain are tangential. If we cut a plank and see the cathedral grain, look at the end cut. You will see long arcs moving in the long dimension of the rectangle of the end cut. This is what we don't want. This shrinkage will be the worst case. My plank was like this, so it was sawn in .75" wide strips and the resulting 1.5" strips were turned 90 degress and glued up into the baffles.
This makes the shrinkage move radially to the heart of the tree and it reduces it to .125" per foot. Still not ideal, but I wanted to try oak for the first time in this application. The wood does not move appreciably on the length of the baffle, about 1/100" per foot. Later in the build, when the baffles are milled for the drivers and attachment to the cabinet, some techniques to prevent the baffle from bowing or splitting will be discussed.
Next post will be about the cabinet cutout and joint construction.
Cheers, Fred
ops: He does waaaay better drawings than I do. I'm sorry it's not as clear as some of the CAD drawings we were fortunate enough to have fellow DIY'ers contribute to other project. 
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