Using Sheet Metal to Make Audio Component Enclosures

While audio face fronts made from nice, pretty, gracefully flowing, polished, textured machined aluminum is one way to make an audio component, it’s not the only way. Very often, while the front of the amp, preamp, DAC or other component might be aluminum, chances are the rest of the component is not. In fact, there is a wealth of equipment made today that doesn’t have any machined aluminum at all. 

Fabricated sheet metal is perhaps one of the largest segments of specialty manufacturing in the metals industry. This is a process that takes a sheet of metal, be it steel, stainless or even aluminum, and cuts, stamps, bends, forms and assembles it into a final configuration. 

Fabricated sheet metal can generally be divided into two groups – those parts made with custom tooling and those without. Tooling is expensive. Period. For high volume applications, tooling can be amortized into the unit cost more easily because of a higher number of parts produced. For low volume applications, and high-end audio certainly qualifies, making an enclosure for a component is more easily, and economically accomplished with equipment that does not use custom tooling. 

Let’s say we want to build an enclosure for an amp. Our “box” as it were, will be made entirely from sheet metal. No machined aluminum front faceplates. Because of lower yearly volume, tooling for a more automated manufacturing process is out. We’ll do this box with other types of equipment. 

First, we need to cut the metal. Most metal, the kind we will be using anyway, comes in flat sheets. A typical size is 4′ X 8′ although there are other equally popular sizes. We first need to cut out the “lay flat” shape, that is, the overall shape of the enclosure minus any bends. If we are making a box, like we’ll be using for our amp, we will very likely form the bottom and sides first. Then we’ll make the top, back plate and front faceplate. 

There are a variety of ways to cut our lay flat blanks. One popular way is with a laser cutter. Other methods include water jet and plasma cutters. However, laser cutters work very well for our application. First, the sheet of metal is loaded on the laser cutter. Second, the part drawing is loaded in the machine and the laser goes to work. When finished, there will be multiple copies of the parts needed to bend our box. Sounds simple, right? Not so much. 

First, a skilled operator is needed to load the part drawings into the onboard computer on the laser cuter. Second, someone has to load the metal sheets, unload the blanks, and repeat the process (unless the fabrication company has heavily invested in automated material handling systems and robotic parts offloading). All of this labor is performed with high cost per hour operators because of the level of skill needed to operate the equipment. There will also be scrap that adds to the cost. 

Once the blanks are finished the most common machine used to make close tolerance, repeatable bends is a press brake. Press brakes can be a couple of feet long to something as large as an 18-wheel truck. Downforce is expressed in tons. Higher tonnage is required for larger designs, heavier gauges of metal and very often, more complex bends. 

The press brake will usually have a variety of onboard tooling. To make a square box will require a number of 90-degree bends. The bottom and sides will be formed from one piece of metal. If the top has any bends, it will be done as a separate process. Same for the front and back plates. 

We are not finished, however. We need to remove the sharp burs caused by all the cutting, bending and handling. Our amp enclosure will also need finishing, be it wet paint or powder coat paint, or probably most common, anodizing. This is a very specialized process that involves dipping the metal parts in a variety of solutions, some as harmless as water, others highly caustic.

Because of the potential for groundwater and air contamination, any company finishing products has the EPA visiting quite often. There are expensive systems required for vapor reclamation for paint lines and containment systems for anodizing tanks. Lastly, front faceplates will need to be screen or pad printed with things like “volume,” “balance,” “source,” and so on. All of this expensive equipment, as well as labor costs affects the selling price of the finished component. 

Also necessary are all the various fasteners required to assemble the top, front and back and also the assortment of parts that will go inside the amp. These include circuit boards, power supplies, transformers and so on. There are a variety of methods to insert these fasteners. All of them are costly because of the amount of labor required to do so. 

Generally speaking, the various parts will be packaged separately and shipped to the company building the amp. Sheet metal fabrication is a multi-step process. One that is deliberate and relatively slow as compared to high speed, high volume manufacturing using more automated equipment and tooling. Each step requires a different process, different machine, machine operator, and most importantly – an additional cost center. Different shops apply different labor burdens to different machines and processes. Not all shops have cutting, forming and finishing equipment under one roof so that requires sending the parts to a secondary supplier, and a whole new series of cost parameters and shipping costs. 

In sheet metal fabrication time = money. Spend more time making a part, the more expensive it will be. The average black anodized component enclosure has been cut out as a blank, formed, deburred, had fasteners mounted inside, anodized (or painted), packaged and shipped. When the company making the amp receives the shipment, they must put all the electronics in the box, adhere the top, back and front, package the amp in elaborate packaging and ship it to the customer. 

Time = Money. There is a lot of time spent making an enclosure out of sheet metal. All of these steps in the process not requiring a heavy investment in custom tooling require time. And just like more expensive machined front face plates, the more steps spent making something, the more time it takes to make it, the more handling is required to make it, and inevitably, the more it will cost to make it. 

While a sheet metal enclosure and faceplate are typically less expensive than its machined from bar stock cousin, it is in no way a “cheap” process. It is a significant cost center in the overall pricing used to make high-end components. Most importantly, it is a commanding cost center in determining the selling price of a stereo component. So the next time you see a component with a sheet metal enclosure and think “cheap,” think again. Cause it’s not.