Build a Custom Fiberglass Subwoofer Box

Building a custom enclosure is a complex, time-consuming, and difficult task. Be patient and do your research ahead of time. This article will guide you through planning, constructing, and detailing your own enclosure.

Steps

  1. Determine the size of the enclosure. The specific speakers/drivers you use will have their own requirements and recommended enclosure volumes. Determine the inside air volume necessary to produce an adequate amount of pressure.
  2. Determine the enclosure's type.
    • Sealed enclosures are best for tighter bass and driver response, but do not offer the same amount of bass resonance as other types.
    • Ported enclosures produce additional, deeper bass, but at the cost of of mid-range bass and tight responses.
    • Band-pass enclosures are a special design that provide exceptional response at a specific frequency range. They are not suitable for all drivers or all types of music.
  3. Make your pattern. Use cardboard, tape, and glue to form the shape.
  4. Apply fiberglass resin and mat to the surfaces.
  5. Cut the box in half, then in half again. The fiberglass box is now larger than the pattern.
  6. Remove cardboard from the inside. Lap joints 3/4" (all equal).
  7. Use pop rivets or other fasteners to assemble the box.
  8. Apply additional fiberglass resin and mat again while maintaining a flat and uniform thickness. Two coats of resin and mat will be extremely strong. Use an automotive body filler, such as Bondo, to further strengthen and seal the box.
  9. Sand as needed. Start with a 40 or 60-grit sandpaper to even out uneven or rough areas. Move up to a 200-grit or higher sandpaper to finalize the finish.
  10. Coat the inside and outside with resin.
  11. Use polyfill inside the enclosure if additional air volume is desired. Polyfill will dampen the pressure inside the enclosure to simulate a greater overall air volume.
  12. Finish with auto paint, auto carpet, or leather.



Tips

  • Apply as smooth as possible. Sanding takes a lot longer than applying little more effort.
  • Periodically check that the box fits where you want it, and visualize the finished product.
  • Do something different; change the color, shape, and placement of the enclosure. There are plenty of pre-built, inexpensive enclosures for sale. Therefore, your goal should be to build your own enclosure for your own custom needs and/or appearance.
  • Always have a drawn image with the measurements.

Warnings

  • Polyester Resin produces toxic fumes.
  • Sanding fiberglass produces toxic dust.
  • Do not leave any air bubbles between the layers. This will weaken the structure and possibly promote vibration of the enclosure. Air bubbles will also create a pitted exterior surface, requiring further cosmetic work.
  • Avoid mounting free-air drivers in an enclosure, unless your enclosure will utilize the entire space of your trunk.

Things You'll Need

  • Plenty of disposable gloves
  • Respirator
  • Cardboard
  • Gallons resin
  • {{safesubst:#invoke:convert|convert}} of mat
  • Putty knives
  • Disposable brushes
  • Disposable mixing containers
  • Plastic protection
  • Gallon chopped glass
  • Bandsaw
  •  Belt sander
  •  Air board
  • 6" to 9" DA sander"
  • DA sander
  • Body Filler
  • Quart containers
  • Mixing Sticks
  • Catalyst dispenser
  • MM syringes
  • Butcher Paper

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