The purpose of a subwoofer enclosure is to separate the sound generated from the front of the subwoofer from the sound generated by the rear of the subwoofer. To answer your question: "Why is this necessary?" If you run a subwoofer in a "free-air" environment - which means no enclosure or baffle to separate the front from the rear - the sound waves coming from the front of the sub woofer are essentially cancelled out by the sound wave created from the rear of the sub woofer.
This is called "Cancellation", and happens because they are out-of-phase with each other. The polarity, along with power and other factors from the amplifier, control the movement of the subwoofer that create the sound waves. To aid as a visual of what is happening with the sound wave, imagine glassy smooth water disturbed by two pebbles dropped only 2 feet apart and the ripples in the surface of the water, radiating outward toward each other. A ripple traveling in one direction with another ripple approaching from a short distance away, the two will CRASH and disrupt the flow of both ripples. This is what happens without using a sub box enclosure.
A quality designed prefabricated speaker cabinet from a respected manufacture is really tough to beat. When it comes to convenience and price of the prefabricated subwoofer enclosures not to mention the seemingly endless selection, it’s not hard to think that the only question would be: "which one do I buy?" After trying many different manufacturers of Sub boxes we found ATRENDS to have the highest standards in manufacturing, fit and finish with the best selection of designs available.
The sub enclosure you choose contributes to the quality of the subsonic acoustics of the subwoofer you purchased for your car audio system. With the endless design combinations of prefabricated subwoofer enclosures available on the market today, you have to ask yourself, "How do I choose the right one." A few things to consider after you have got past the obvious usual considerations of size, shape, colour and price would be:
If you are unable to find the right prefabricated sub box for your application then maybe a custom built woofer enclosure would be more suitable for your needs. The advantage to a custom built cabinet is not only acoustic but also fit and finish. You are able to control every aspect of a custom box from acoustic tuning, style and design, building materials to colour and finish. This flexibility of creative freedom and unique one of a kind design usually comes with a price tag relative to the complexity not to mention unlimited bragging rights.
When building a sub box to suit your specific set of requirements there are many factors to consider.
Two popular materials to build Subwoofer enclosures are: MDF and Fiberglass.
MDF also known as "Medium Density Fibre" board is the traditional product of choice for constructing a subwoofer box. This manmade product is very stable, flat and relatively user friendly to build with. Although MDF is easy to cut and shape with traditional wood working tools, the by-product of construction is the nasty dust that needs to be properly managed during the fabrication process with a dust collection system. A good wood shop outfitted with a table saw, router table and patterns amongst other popular hand held tools, is adequate to take on a custom project. MDF does have a few drawbacks: It’s bulky and heavy and does not resist moisture at all. When the application calls for maximizing space and contouring complex shapes or has high moisture concerns, "Fibreglass" is a fantastic alternative that will stand up to these challenges.
Fibreglass is a unique medium that has unlimited possibilities of custom fabrication. The flexibility to adapt to almost any shape is one of the most popular advantages of fibreglass as a building material. In its raw state, fibreglass can be moulded into any contour and with multiple layers has a strength unmatched by any other comparable product for the price. During construction the toxic fumes and unique skill set requirements needed to work with this material make fibreglass fabrication a job for the trained professional.