Tim,
You described your listening area as 16'x42'x10'. Which wall is the
"back" wall? What is the orientation in this "long" room. It's a good size
but, the way you described the speaker arrangement, I sense
competition for floor space?
About the sealed enclosures you will be building; the 12 cu/ft. is a
work around figure and the shape is quite flexible. If you build the
enclosure to a Vb of 12 cu/ft, and you fill it with appropriate stuffing,
the (effective) volume will inflate 10% to 20% depending on the
material, quantity, and density. Does that mean you could make the
cabinet smaller? Technically yes, but then there is all the internal
bracing and sub panels that will be required to reinforce the internal
structure, and so, that displacement will offset some of the volume
gained by the stuffing. So stay around 12 cu/ft and all will be good.
There is some debate about the material called acoustic
stuffing. There are two camps, old school fiberglass and the newer
synthetic grades of polyfill. Considering the amount you will need, I
would suggest a combination of the two. Because of it's higher thermal
absorption properties, fiberglass is deemed superior to
polyfill. IMHO, I can hear the difference. Even though I advocate
fiberglass, there is the problem of glass particles going where they
shouldn't, like your lungs and the itchy annoyance on your skin. Ok,
wear a mask, gloves, and seal up the cabinet, so what's the problem?
While most quality speakers are properly sealed against dust in
general, reducing particles in the cabinet is still desirable. I use
both, the superiority of fiberglass as the majority fill AND, and a single
layer of polyfill, over it all, for containment. The best of both worlds. If
you have a problem with fiberglass use all polyfill. Acoustic grade
polyfill is quite expensive compared to fiberglass.
Since you'll be cutting from 4'x8' sheets of MDF or plywood, certain
dimensions reduce scrap better than others. For example, I would
consider setting the fence to (23" & 1/4") and cross cutting (16) (23 &
1/4") x 48" panels from (3) sheets. Now you have the front, back, sides
and the additional sections from where the top, bottom and internal
panels will be cross cut from all cut. The front, back, top, bottom and
inside panels are all 23 1/4" in width, and therefore form the inside
portion of the cabinet. Think of a simple book case. The top, bottom
and all the shelves are the same width, and they all fit in between
(inside) the sides.
Now, you should define what 48" panel will be the front, back, and
which will be the sides. They're all the same so get out a marker and
make one a face. Designate inside, outside and what side is up. Once
you have marked front, back, and sides; break out the pipe clamps and
butt joint the sides (no glue), to the front and back (inside) to
form a tower. If you look at the face (or back), you should see the 3/4"
edges of the sides only, as the edges of the face and back are inside
the butt joint. The reason for this, is to visualize how the cabinet will
assemble, and at this stage, the depth of the top
and bottom (and internal) panels. Along the top, measure the inside of
the top edge of the face to the inside edge of the back. It should
(23 & 1/4)" - (1 & 1/2)" = (21 & 3/4)". Set the fence to this dimension
and cut the (4) panels.
Note (1 & 1/2)" is twice the depth (3/4") of the panel
One last thing, 48" is to high to produce 12 cu/ft.
Inside dimensions; volume= WxDxH
(23" & 1/2")x(21" & 3/4")x(48") = 24,534cu/in
Note; 12x12x12=1728 cu/in = 1 cu/ft
Therefore; 24,534 cu/in / 1728 cu/in = 14.2 cu/ft
The driver would love the extra volume, but a space conscious user
might not.
Inside dimensions; volume = WxDx(40")
(23 & 1/2)" x (21 & 3/4)" x (41)" = 20,956.13 cu/in
20,956.13 cu/in / 1728 cu/in = 12.13 cu/ft
There are more details, but chew on this for the time being.
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