When building a sub box, there are many things to consider in order to achieve the sound you are looking for. A big thing to remember, is the box should always be built to the specs of the sub woofer that you are building the box for. For instance, if the box is too small or too large you can have distortion and even damage the sub woofer Each sub you plan to install should also have its own enclosure. This is in case you have two sub woofers in one box and one blows, then the other is left with too much volume (area) and can damage it. You should always calculate the volume of the box regardless of its shape.
With that being said, there are three main types of sub woofer enclosures. Sealed, Ported, and Bandpass. Sealed boxes provide the listener with a solid and responsive bass tone, not too “boomy”. A Ported box will give the sub woofer more air flow allowing it to provide a lower bass sound. Bandpass boxes are a mix, they allow air flow for a sub, that is sealed at one end of a box facing inwards. These setups definitely trickier, but allow for precise tuning. Again calculate the volume of the box properly for your setup.
Building your box, try to make it very sturdy. Most common materials used are Pressboard, MDF (Medium Density Fiberboard), and sometimes Plexiglass. Your materials should be 5/8″ to 1″ thick, if using Plexiglass, no less than 1/2″. Some people use fiberglass, which is tough to work with and requires many layers to get a smooth finish. It is also a good idea brace your box, extra support never hurts. If you are building a ported box, the most common material used is PVC, it comes in many diameters and is very sturdy. Be sure to make your holes for wiring and any ports as close to perfect as possible, this will reduce any gaps.
When doing this the space the port takes up must be calculated into the dimensions of the box. Once you have your basic structure built, use a sealant or glue to fill in the gaps on the inside of the box, this will increase sound quality. Be sure to let the glue fully cure before installing any sub woofers Then reinforce the joints by using some wood screws about 2 – 2.5″ inches long. You will want to space them out about every 4″ or so. Make sure to pre-drill holes for the screws, this way you are less likely to split the wood. You will then want to dampen the sound on the inside of the box. This reduces the high end frequency resonance. Common dampeners are pillow polyfill, fiberglass insulation, and tar based sprays.
For the outside of the box, you will want to decide early on, whether you are going to paint it or cover the exterior with carpet or vinyl. If you choose to paint the exterior of the box, use a wood filler to fill in all of the blemishes on the outside. Be sure to always use a primer before applying paint. Most people choose to carpet the outside or cover it with vinyl, its a great way to hide any flaws on the exterior of the box.
First make sure you piece of material is long enough to cover the whole box. Apply some glue or adhesive to the box and the carpet/vinyl and start in the middle. Work your way out one side at a time being sure to leave the end of the material where it will not be visible. Stretching the carpet or vinyl will provide a smoother look. Then if you like you can add some heavy staples to the ends to help hold it tight. Then once the box is built you can proceed with your wiring and installing of the sub woofers.
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