Plastic, Fiberglass or Wood for Car Audio?

Posted on 22. Jul, 2009 by in Q Logic Products

sb2-2-3When discussing Q-Logic Q-Forms or Q-Customs, often I get the same question- Why Plastic? With all of the different types of materials available, why use plastic, why not wood or fiberglass? There are several answers to this question, and I will get to all of them.

Wood- Wood is great for the basic flat enclosure. It is cheap, dense, rigid and easy to work with, which is why it is the single most common type of material used for subwoofer enclosures. The problem with wood is that it is hard to bend. It can be bent and molded to a point, but mimicking the shapes of a car is way beyond what regular wood is capable of.

Fiberglass- This stuff is awesome. It can be formed to any shape, it’s strong as hell, super lightweight and costs a fortune. Oh wait, that is not a good thing. The price of fiberglass resin is expensive, and it keeps going up. Five years ago, the price for a gallon of resin was around $30, now it closer to $60. Considering that you can easily use 2 or 3 gallons in even a small two-10” sub enclosure or a gallon of resin for a pair of kickpanels means that the project becomes very expensive. While fiberglass is very strong and resists flexing (to the point that it just breaks), building tooling molds for fiberglass is more expensive than the materials to make the part. The molds must be two or more parts and it takes around a day to make a single set of parts from one mold, depending on the size of the part. This makes it cost prohibitive for use in our type of manufacturing. Sure, building a show car with fiberglass molds is not a big deal, you are only going pull a few parts from each mold and you have bigger budget, but for mass-production, it simply is not worth it.

There are several different types of plastics that are used for manufacturing. I am going to touch on the three most common types.

Roto-molded plastic- Roto-molding uses a metal tool (typically aluminum) that is cut to resemble the exterior shape. This allows you to reproduce a part the same every time with the exact dimensions and detail. Roto-molding uses plastic beads or pellets that are slowly heated up until they flow like liquid. During this process, the tooling spins around, spreading the liquid plastic over the interior surface of the tooling. This is commonly used for hollow parts. The tooling is expensive and so is the machinery to make the parts, so much so that these parts are typically Chinese made. These parts take hours to complete, thus further increasing the cost.

Injection-molded plastic- Another liquid-plastic method is injection molding. Similar to roto-molding, injection molding features specialized tooling that forms both the inside and outside of the plastic. This allows you to create things like mounting studs, stiffening ribs and other details on either side of the plastic. Just about every plastic housing you have ever seen is injection molded, radios, TV cases, telephones, these are almost all exclusively injection-molded. The tooling is expensive, so these parts must be mass produced on a large scale in order to overcome the price.

Vacuum-formed plastic- While there are several ways to use vacuum-forming (vac-forming for short), the most common is a single-sided tool that is pressed into a hot sheet of plastic. Once the plastic is pressed into the sheet, the air is sucked out of in between the tool and the plastic. This pulls the plastic into the details of the tooling and forms the part. This is the most economical method of plastic forming, as it is quick, relatively easy and the tooling does not cost near as much. This means that you can build more parts and sell them for less. This is why a pair of Q-Forms only cost a couple hundred bucks and not $600.

Custom-built kickpanels at a specialty shop will cost easily $1500, a custom fiberglass enclosure can break the bank with ease, but a Q-Custom and a set of Q-Forms might set you back $500, definitely a bargain and you will know what they look like before you buy! I have seen some truly fugly “professional” built kickpanels and enclosures.

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One Response to “Plastic, Fiberglass or Wood for Car Audio?”

  1. cole

    29. Jul, 2009

    Good info. Thanks for explaining the differences.

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