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Building Easy Fiberglass Door Enclosures

The following directions should aid in the design, preparation, production, and installation of sealed door enclosures using a minimum of skill.
Supplies needed:
     Fiberglass cloth
     Fiberglass mat
     Fiberglass resin w/hardener
     stapler or tacks
     .75" MDF or plywood or hardboard
     disposable mixing tray (for fiberglass resin)
     5 or more cheap paint brushes
     Silicone sealant
     1" to 2" sheetrock screws (or any good screws you have)
     screwdriver to fit above screws
     Measuring tape/ruler
     saw (jig, circular, radial, whatever)
     removable tape
     spray adhesive/glue
     drill (and drill bits)
     weather stripping (.25" or .5" thick dependant on speaker mounting location)

If using a sub/midrange where Theil-Small params are avail, model the speaker to determine appropriate air space. Hi-end mids (like my Quart 6.5"ers) require up to .4cf of airspace. If speaker is a standard 6.5"-5.25" mid or co-ax, we will make the enclosure just large enough to create a sealed enclosure around the speaker.

Step 1.
First, determine your speaker location and, if necessary, cut the hole for the speaker. Make sure the speaker fits properly. Area around speaker needs to be clear of any window mounts/internal gadgets.

Step 2.
Use the tape measurer/ruler and determine the depth of the door around the speaker hole. The depth should be at a minimum of 1/2" deeper than the mounting depth of the speaker. At this point, you should have one of the necessary measurements to calculate the volume of the enclosure if applicable. If using TS params, determine proper w/h of enclosure to get proper airspace requirements. Remember to subtract the magnet structure and basket from those calculations.

     Note: The depth of the enclosure should allow enough clearance for the window (if applicable).
     Keep the depth of the enclosure at least .5" away from the window.

Step 3.
At this point, you should have an outline of the enclosure. If using standard mid/coax, we will build the enclosure just large enough to surround the speaker. For a 6.5" driver, a 7"(h) x 7" (d) should suffice. If using a standard driver and the 7x7xdepth method, you should now be ready to make your board cuts.

For the above, using .75" wood, the cuts should be:

          2ea 7" x depth
          2ea 5.5" x depth

You will now have four small boards that, when put together in a square, should be 7" x 7" x depth.

     If using TS params:
          Determine a good width or height for the enclosure, times that with the depth measurement to
          get a number. Then divide the total required square inches by that number. The outcome
          should be the length of the last outer diameter. Example:

          Your speaker design requires .2 cf of airspace plus the speakers magnet and basket assy
          (at 50 sq in ?). This equals 395.6 cubic inches (345.6 + 50). Your depth for the speaker
          is 3.5" and you have determined that the maximum box height can be 10". Since 10" is
          external dimensions, and we need internal dimensions, we must subtract the width of
          the wood (.75 + .75=1.5). We now have 8.5" id (internal dimensions). Since 3.5" is the
          depth, we really don't need to deduct from this.

          Now the math:
               8.5" x 3.5" = 29.75"
          Now for missing link:
               395.6" / 29.75" = 13.3" id (rounded)
          Now, since 13.3" is id, we need to add 1.5" for od.
               13.3" + 1.5" = 14.8" od
          You now have the outer diameter of your enclosures sides:
               10"h x 14.8"w x 3.5"d
          For the above, using .75" wood, the cuts should be:
               2ea 14.8" x 3.5"
               2ea 8.5" x 3.5"
          You will now have four small boards that, when put together in a square, should be:
            14.8w x 10"h x 3.5"d

Step 4.
Now that you have measurements, you can measure the outline on the door and pre-drill holes for mounting screws. If not sure, you can tape the enclosure together and use it to draw its outline on the door, then pre-drill the holes.

Step 5.
Now, take the pieces of wood to a work area and lay them out to form the enclosure (if you taped them together, you should already be in this configuration). Use tape to keep the enclosure in this configuration. Now, using the fiberglass cloth, cut a piece that will fit over the back of the enclosure and slightly overlap the sides. Start at one corner and staple the cloth to the back of the enclosure. Make is tight, but not too tight. Now, use the spray adhesive/glue to affix the overlapped sides. DO NOT use glue on the corner cloth pieces, keep the glue at least .5-1" from the corners of the enclosure. You should now have a square box (taped) with the cloth forming the back of the enclosure.

Step 6.
Mix an ounce or so of the fiberglass resin with the hardener. Using a paint brush, spread the resin over the fiberglass cloth where it meets the wood. You should cover the cloth ONLY where it touches wood. Again, DO NOT put the resin on the corner cloth pieces, keep it at least .5-1" away from the corners. Make sure you coat the cloth where it overlaps to the sides of the enclosure. Also, coat the wood where it will be connecting to the skin of the car, ALL of the wood should be covered with resin except the corners of the enclosure. Use two coats if necessary. After allowing to dry/harden, you should now have a square box with the cloth forming the back of the enclosure with the cloth fiberglassed to the wood on the sides and back of the enclosure. The back of the enclosure should still be cloth and the corners (and around the corners) should still be cloth.

Step 7.
Remove the tape from the corners of the enclosure after the resin has cured. This should leave you with a "floppy" enclosure. Now, holding the upper right on the enclosure (right hand) and the lower left of the enclosure (left hand), twist the enclosure by pulling up with your right hand while pulling down with the left. This should "fold" the enclosure. Do not worry if the cloth at the corners gets pulls or slightly tears. Only fold it enough to get the enclosure into the opening of the speaker. With a little work, you should be able to work the enclosure into the door. Once into the door, start arranging the enclosure into its new home. Screw the enclosure into place using the pre-drilled holes done previously (make sure the cloth end is toward the window). Take your time. If done right, you should now have the enclosure mounted onto the inner door skin. The cloth back of the enclosure should be relatively tight. At this point, make sure the window can roll down properly and that the window does not "slap" the enclosure when the door is closed with the window in the down position. If problems exist, remove the enclosure and make necessary modifications. Also, be careful with tinted windows while testing.

Step 8.
Mix a good amount of resin. Using another paint brush, coat the fiberglass cloth on the back of the enclosure (you may want to put newspaper or paper towels in the bottom of the door to pickup any extra resin that may run down the door). Use enough resin so that their are limited holes in the cloth backing. At this same time, thoroughly coat the outside and outer corners of the wood. Make sure all corners are pressed down to the wood and the wood is saturated in resin. This will keep moisture from ruining your enclosure in the future (do it right the first time). After the first coat is completely dry, proceed with a second coat to the back of the enclosure. After this coat has cured, you should have a relatively sealed fiberglass back to the enclosure.

          Note: While performing steps 8 and 9, use extra resin to coat the inside wood and corners of the enclosure.

Step 9.
Cut a piece of fiberglass mat that will fit the inside of the enclosure and overlap the inner sides. Using spray adhesive, work this piece into place inside the enclosure. Using more resin and another paint brush, coat the fiberglass. The mat material will be clear(ish) when coated properly and should not be white. After this has cured, repeat this process. If you are using standard mids, this should be enough fiberglass. If using high-powered mids/mid-bass drivers, another one to two applications of mat may be needed.

Step 10.
After the fiberglass has cured, seal the outside and the inside of the enclosure (where it is affixed to the door skin) with silicone. Again, give a little extra effort now to do it right the first time.

Step 11.
Using a drill, drill a hole for the speaker wire through a wood side. Once the speaker wire has been pushed through, seal the hole with silicone.

Step 12.
Lightly add a little polyfill to the enclosure. Do not stuff it!

Step 13.
Connect and mount the speaker. Use of weather stripping is to be used around the speaker to ensure an air-tight seal.

You are now through. You have just completed creating sealed enclosures in your doors. Pat yourself on the back and have a beer! Enjoy!!!

Disclaimer: The author will not be held responsible nor held liable for any damages due to these instructions. Anyone following these directions are doing so at their own risk. This Documentation may not be distributed without the authors consent.


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