Using Aluminum Extrusions for Audio Applications

While machining and metal fabrication are the most popular types of metals manufacturing used in high performance audio, there is one other that is used, albeit not as widespread as the other two. That process is aluminum extrusions. 

Aluminum extrusions are generally used as a “skeleton” for speakers. Why? Well, the aluminum framework adds rigidity to the speakers, helps make the cabinets more inert, and helps lower resonances which lead to all sorts of sonic nightmares. It also makes the speaker heavier and depending on how it is assembled and the level of the drivers and crossover network, it could conceivably make the speaker more expensive to manufacture. Heatsinks, used primarily on amplifiers, are another application. And when talking about cost, I refer ONLY to the cost to manufacture the component, not the selling price. That is a marketing and management decision, but it obviously starts with how much something costs to build. 

Remember Play-Doh? Fun stuff. You could mold, squeeze and do all sorts of things with it. Play-Doh had a “Fun Factory” where “Doh” was loaded into a hopper, a handle was depressed into the hopper and the Doh was squeezed out through a star, tube or any of an assortment of inserts to make a shape. If you remember this toy, you have a working idea how extrusions are made. 

Aluminum is an alloy. Various base elements are mixed together to form that alloy. The exact chemical composition may be tailored to achieve specific mechanical properties. Aluminum extrusions must also be artificially aged, or “tempered.” Tempering is a process that speeds up natural aging and is performed at specific temperatures, pressures and time. 

One of the most popular alloys used in the US is called 6063. It is the workhorse of the extrusion industry. Two popular tempers used are T6 and T4. A T6 temper is harder and is usually used in applications where straight lengths will be cut, drilled, tapped, and assembled. T4 is softer than T6 and is commonly used in applications where bending of the metal is required. Needless to say, there are many, many alloys and a wide variety of tempers. But certainly, 6063 – T6 is a very popular alloy used in aluminum extrusions. What audio manufacturers use, however, may be different. 

For processing, the metal is heated until soft, how much depends on the profile, wall thickness and the shape of the final part. A ram pushes the softened metal through a die, much like Play-Doh, and the profile comes out. Once the required length has been extruded the metal is cut, pulled from both ends to straighten, and sent to tempering. 

Dies are custom and are typically paid for by the customer. These dies may easily range in cost from a few thousand dollars to tens of thousands of dollars. If the extrusion will be cut to a specific length, drilled, tapped and machined for assembly, then fixtures will be needed to assure close tolerance and repeatability. Bolting part “A” to part “B” must be repeatable with holes that consistently match. Fixtures ensure the holes are drilled in the same exact location each time. 

If welding will take place, welding fixtures are usually required for the same reason. It may also, depending on the part design, be necessary to machine a chamfer into both pieces of metal to give the weld someplace to go. Again, this varies on the design and required mechanical properties. 

Once machined, welded and / or assembled, the framework or heatsink is ready to be used in an audio application. 

It should be obvious where much of the cost originates. Tooling (or dies), fixtures, the cost of the metal and most importantly all the labor required to make the end use product can be very, very expensive. Spending tens of thousands of dollars on tooling to make the extrusion, thousands and thousands of dollars for fixtures and probably most expensive of all, labor costs quickly add up.  While tooling and fixtures are one-time costs, they must be paid in advanced, likewise affecting cash flow. 

Another issue is most extrusion companies prefer orders of a certain size to make setting up the machine worthwhile. Many, not all of course, but many require a minimum of 1000 pounds of metal — per profile. If your application is using fifty pounds, well, ya gotta buy a lot of metal. If you have multiple profiles, then your tooling and fixturing costs, and also order requirements are multiplied by the number of profiles. Likewise, the cost of inventory now enters the mix. Yes, there are companies that specialize in low volume orders, but their pricing is typically more expensive because someone must pay for set up and inventory costs. 

It is true that extrusions are perhaps the least used metal process in high performance audio. It’s is no less difficult and expensive as it applies to what audio companies face when making a product. 

Machining, fabrication and extrusions are used both for structural as well as cosmetic purposes. While they do serve a function, each comes at a considerable cost. Much of that cost is paying for multiple steps in processing, tooling, fixtures and the part itself. Labor is expensive. And machine operators these days are highly skilled and command top dollar. The last thing a manufacturer wants is to lose a skilled CNC operator because a competitor offered a $1.00 more per hour raise. 

It is very easy for us, as consumers to look at the cost of a component and think there is no way it should cost that much.

And yes, absolutely, some companies add considerable profit to their sale price. Others do not. But those are management and marketing decisions. In these three articles I have tried to point out that the overall cost of stereo equipment is more than power supplies and circuit boards.  Metal, whether machined, fabricated or extruded is also a significant cost center and a major consideration in determining the cost to make something. 

It is very easy to simply assume that a $20,000 amp costs $2000 to make and there is $18,000 in profit. I’m sure there are many who feel that is true. When you look at the actual costs of the associated component parts in making stereo gear, it is easy to see that is not the case at all.