Most headphone housings are cast or moulded. You make a tool once, you pour ten thousand shells, and each one costs less than the box it ships in. It is the sensible way to build a product. SG-01 is not built that way, and people ask why often enough that we should write it down.
Every SG-01 shell starts as a 90 by 90 by 45 millimetre block of 6061 aluminium. A five-axis machine removes roughly 78 percent of it over 41 minutes. What is left is a single piece with the driver seat, the hinge boss, the vent channels and the pad lip all cut from the same grain, with no seams, no inserts and nothing glued.
The acoustic reason
A cast shell rings. Not audibly, but measurably, with a resonance somewhere between 2 and 4 kHz depending on wall thickness. You can damp it with foam and rubber, and most brands do. We would rather not have it. A milled shell has a uniform wall, a known mass and a resonance we can place above 9 kHz, where the driver is not asking it for anything. The result is a housing that gets out of the way, which is the only job a housing has.
The repair reason
Because the hinge boss is part of the shell, a dropped pair does not crack at a glued joint. It dents, and a dent is cosmetic. Because the pad lip is machined rather than moulded, the tolerance is tight enough that pads from the first run still seat on shells from the fourth. That matters more to us than the unit cost, since we promise ten years of parts and we mean to keep it.
The number nobody likes
The honest cost of a milled shell is about eleven times a cast one, before anodising. It is the single most expensive decision in the product, and it is why SG-01 is sold in runs of 2,000 rather than continuously. We can book the machines for a run. We cannot book them forever.
The offcuts from a run of 2,000 shells weigh 340 kilos. That is where Metal Object 03 came from.
Studio production notes, Drop 03
We know this is not the efficient answer. It is the one we can stand behind for a decade, which is how long we expect a pair to last. If you want to see what the process looks like, the CNC week panel on the studio page has the footage, and the next open day is on the contact page.
