Materials For Construction
 

In the construction of an autosound system, many materials of different properties are used. Often, people do not appreciate what a wide range of materials are in use today, or how to get them. In this paper I will discuss some materials, their advantages and disadvantages, and finally, where to get them.

  • Wood, MDF, HDF, Masonite, and Particle Board
  • Fiberglass
  • Bondo™, Body Filler
  • Epoxy, Resin
  • Plaster of Paris, Clay
  • Vinyl, Cloth, Leather, Grille Cloth
  • ABS Plastic
  • Aluminum, Copper, Steel, and other Metals
  • Plexiglass™, Acrylic Sheet
  • PVC
  • Glass
  • Paints
  • Adhesives
  • Clay

 

The first and most obvious material for construction is wood. Wood, and all other tree related materials, are common, cheap, and fairly easy to work with. Natural grain wood is actually rare, however. Most wood is not dense and dead enough (acoustically dead, that is) to avoid harsh resonances which color music. That's why MDF and HDF is used so much by professional installers for enclosure construction and panel fabrication. That is not to say natural wood is not used. Many audiophiles prefer Birch, or more specifically, 3/4" 7 ply Russian Birch (is guud strrrrong rrrushin vood, no). This wood is extremely dense, and fairly heavy, and a 6x8 sheet is roughly $55. Also, wood veneer made of Oak, Pine, Burlwood, Walnut, Pecan, or Teak is used to trim panels or accent an installation. Nothing can be said to be more visually pleasing than a well colored and finished natural wood grain (except maybe a nekked honey baby with a six pack). As nice as wood is, the expense makes it impractical for hidden panels or carpeted enclosures. Enter, Fiberboard. MDF and HDF are quite a bit less expensive, and offer the same dense and acoustically dead properties as hardwoods. A little note: Masonite is often confused as an individual material, it is actually a brand name for HDF. MDF stands for Medium Density Fiberboard, and HDF is (obviously) High Density Fiberboard. Both types of wood are basically fine sawdust, which is mixed with resin, then compressed under heat. Same goes for particle board, except with particle board, the sawdust is much less fine. Particle board is not as sturdy as MDF or HDF. All three need good cutting blades to work on, and all three are very easily damaged by water (in fact, Masonite corporation just got it up the ass by consumer groups because of home siding made from Masonite rotting due to water damage). MDF and HDF is most often used for making enclosures, amp racks, and speaker baffles, or whatever.

Fiberglass!!! The miracle material! Fiberglass is often confused with it's component polyester resin. Fiberglass is actually a material made of long glass fibers, spun out and combined together. It is very light. Fiberglass is made into a woven mat for fabrication purposes. Then the resin is painted on. It's the resin that actually does most of the work. Resins are discussed later, along with Epoxy. Fiberglass can be had from any hardware store, or automotive supplier.

Bondo is another trade mark name. Bondo is actually just a ceramic body filler. When the filler is combined with a hardener, it hardens to a point where it is easily sanded. Bondo works best to shape surfaces, or to smooth and round rough edges. Epoxy works in the same manner, but it is more plastic. Epoxy also works better as a bonding agent to combine two objects, and takes seemingly forever to harden (normally, it's about 5 minutes or so, but because you have to hold the two parts together tightly, its seems like forever. Resin also works the same way, but dries relatively quickly. Resin is suitable for wholesale fabrication of panels, or small parts. The best method is to mix up a batch, then brush the mixture onto a porous matting, or even over a cloth. The matting or cloth forms the foundation for the resin, and when the resin dries, it stiffens the cloth or matting considerably. Best of all, with resin, you can easily work with odd shapes. All three of these "cure", not "dry". The difference is, when something dries (like paint, or glue), they give off a by product, like water. However, binary compounds like these cure exothermically. That is, they give off heat in a chemical reaction to occur. Working with them in colder temperatures mean you have to wait longer for them to cure. These are all quite common, and you can commandeer them from any hardware store or autoparts store.

Plaster of Paris, and clay, have their places. Normally, you would use these two materials to make molds, for instance, in which a fiberglass panel would be cast. Rarely would you actually use these materials IN your car, since neither hold up well to the extreme rigors of the automotive environment. However, in fabrication, they can be indispensable tools. An exception would be modeling clay. Once modeling clay cures (notice I said cure, not dry), it's solid. You can use clay to form complex shapes and round corners.

Vinyl, Cloth, Leather, etc, etc, are used to trim and cover your work. Vinyl is very popular, since most automotive manufacturers use vinyl of various grades to cover their doors, seats, and dashes. Vinyl comes in many forms. You will want to get a very stretchable vinyl, the best grades of which are often found at an automotive upholsterers shop. It is also better to get it there because you can get a near exact match for your cars color. One of the nice things about vinyl is that if you heat it, it will become more pliable, and cover curved and uneven surfaces better. Cloth on the other hand, if it is not stretchable enough, needs to be muscled into place. One thing to watch for with fabric is the grain. The grain with vinyl or leather is somewhat random, but cloth has a definite warf and weave. You must be careful to maintain that weave when stretching cloth. Finally, leather. Leather is rarely used, since a good vinyl will look like leather, while leather is much more difficult to use, and more expensive. Leather requires special tools and techniques, but the results are often very nice. Since leather is basically the skin of an animal, conditioners and moisturizers have to be worked into the leather to make it capable of forming. Scraping the inside of the leather also helps, but doing so excessively eventually weakens the leather.

ABS plastic is a cure-all. It normally comes in flat panels, textured or smooth. You can also get it finished with patterns to suit your install, and you can paint it. Grid ABS can be scored on the back, and broken along the grid lines. You can also grind the plastic with a bench grinder, and shape it. By heating the ABS, you can also form it into odd shapes, but usually nothing too complex.

Metals require a lot more skill than the average DIY'er, indeed, might have. For starters, with metal, if you make a mistake, you have to scrap the whole sample, and start over. Also, different metals have different properties, so working with aluminum is different from working with steel. However, the results are fantastic. For working with large amounts of metal, it's a good idea to kiss up to a machinist with a CNC (Computerized Numerical Control) Machining Rig. They not only have the tools, but they have much less expensive access to metal stock. If you are just looking to veneer something, you can buy metal plates at hardware stores. Normally, you will find aluminum in the roofing section where it is used as a splash guard for gutters. Copper, Brass, Steel, and Aluminum can also be found near the doors section, where it is used for kick plates. This metal can be cut with a fine metal cutting blade on a sabre saw or scroll saw. A fine file should be used to file off burrs and smooth edges.

Plexiglass is already widely used in car audio installations. Plexiglass is the brand name for acrylic sheet. The nice thing about plexi is that it's clear, yet tough. Unlike glass, it is very safe to use. Plexi can be formed with heat, and cut with a fine saw blade, but much practice and care must be taken not to screw it up. Plexi in various thicknesses can be purchased at major hardware stores everywhere. Some nicer tricks with plexi is to light it from the end, which makes the panel glow. Also, you can etch plexi like glass, and when lit, the etching glows.

Glass is much less common in installations for a number of reasons. Mainly, it's a safety issue. Broken glass can hurt people and stuff. It's also a pain in the ass to vacuum up. However, glass can absorb much higher temperatures than plastic can, and thus, it still has a use in very high temperature applications. Glass and plexi are very much alike, in that they can both be edge lit, etched, and heat formed, although glass needs a lot more heat than plexi.

Paints are very important. You always want to use the correct type of paint for the surface you are painting. For instance, when painting plastics, it's best to use a paint optimized for plastics. Paints designed for metals may contain harsh solvents which will fugg up plastics. With painting, prep is always very important, and should be taken seriously. More work should go into prep than into the actual painting, for the best results.

At some point, you will need to put all this shit together. Screwing, gluing, and nailing is the way to go. Selecting good glue is important. Hot glue is one of the most useful, but you must get a high temperature glue which will not begin to give under the high temperatures an automotive interior can reach. Hot glue is not a cure-all, however. It lumps up, and should only be used for tacking. For applying cloth or vinyl, spray adhesive is highly recommended. It will allow the material to lay flat, while giving a good bond. 3M Spray Adhesive 77 is probably the best. Rubber cement is also highly useful in bonding surfaces that have to remain flexible. Contact cement is good for touch up (loose edges, etc).

Many other unspecific materials find their uses in car audio fabrication as well. Their uses may be obvious, like superglue, or not so obvious, like beer. Others are less common exotic materials, like Kevlar and carbon fiber. One of the materials I like to use is great stuff foam. Great Stuff is an expanding foam used for sealing large gaps and insulating in home construction. It is also suitable for the same purpose in automobiles. Great Stuff, when dry, can be shaped and formed, and is great for making molds.

Of the many materials used in constructing truly great looking custom work, these are just a few. Never hesitate to experiment with new materials. Experimenting is often the key between an average job, and truly state of the art installations.

by: Andrew Krause