Building A Custom Fiberglass Subwoofer Box

Building a custom enclosure is often too complex and difficult for us to do. However, we believe that with the right directions, patience, and a day of free time on your hands you can create something that you will be able to use and will be proud of the work that you have accomplished.


  • First you need to know the size of the enclosure. Each speaker or drive will have their own measurements and specific enclosure volumes that they can handle. Find out what inside air volume is needed for the right amount of pressure.
  • Make the pattern of the enclosure using cardboard, tape, and glue to help form the shape.
  • Apply the fiberglass resin and mat to the surfaces.
  • Cut the box in half and then in half once more. This will mean that the fiberglass box is larger then the pattern you made.
  • Remove the cardboard. Lap all of the joints ¾” equally.
  • Use a type of fastener like pop rivets to assemble the box.
  • Now you will need to apply more fiberglass resin and mat. During this time you must maintain a flat an equal thickness around the whole area. To make sure that it is extremely strong you should use two coats of resin and mat. You should also use a type of body filler to make it even stronger.
  • Sand it down using a 40 to 60 grit sandpaper to help even out the rough areas. To finish it off use a 200 grit sandpaper.
  • Use resin to coat the in and out of it.
  • Use polyfill inside of the enclosure if you believe that more air volume is needed. This will help to dampen the pressure within and help to simulate more air volume.
  • Lastly you will need to use auto pain, carpet, or leather over it.