A metal earphone housing does a job that plastic cannot: it adds mass where you need damping, it survives being dropped, and it reads as a premium object the moment it is picked up. But earphone metal housing CNC machining is also one of the tightest-tolerance jobs in consumer audio, because the part has to hold a driver, a nozzle, a cable strain relief and a lid — often inside an envelope smaller than a thumb.
This guide covers what drives the design, the alloys that actually get used, the tolerance and finish decisions that separate a housing that assembles cleanly from one that needs hand-fitting, and what to put in an RFQ.
Why Machining Instead of MIG Casting or MIM
Three routes compete for a metal earphone housing: CNC machining from billet, metal injection moulding, and die casting.
| Route | Tooling cost | Unit cost at 100 | Unit cost at 20,000 | Tolerance | Best for |
|---|---|---|---|---|---|
| CNC machining | None | High | Moderate | ±0.01 mm | Prototypes, 50–5,000, premium SKUs |
| MIM | High | Low | Lowest | ±0.03–0.05 mm | 20,000+, simple geometry |
| Die casting | High | Low | Low | ±0.05–0.10 mm | Large shells, non-critical fit |
Machining wins below roughly 5,000 units and for any housing where the driver seat or nozzle bore is dimension-critical. It also wins during development, because a design change costs a CAM update rather than a new mould.
Alloy Selection
| Alloy | Why it is used | Trade-off |
|---|---|---|
| 6063-T6 | Best anodize cosmetics, excellent extrusion-like finish, good for dyed colours | Lower strength than 6061 |
| 6061-T6 | Stronger, widely stocked, good machinability | Slightly less uniform anodize colour on small parts |
| 7075-T6 | Highest strength, allows thinner walls | Colour shift when anodized; higher cost |
| 304 stainless | Weight and wear; used for nozzle and grille rings | 3× the cycle time; heavy |
| Brass / copper | Acoustic damping, distinctive appearance | Tarnishes; needs clear coat |
For most premium in-ear and over-ear housings, 6063-T6 is the default: it anodizes to the most consistent colour, which matters more than strength at this scale. Where the housing carries a threaded lid or a press-fit nozzle, 6061-T6 gives a little more margin against cracking at the thread root.
Our aluminium machining guide covers cutting parameters; the wider audio family is documented in TWS headset shell machining and electroacoustic components.
The Four Features That Decide Whether It Assembles
1. Driver seat
The driver sits on a shoulder or in a bore. Specify the bore diameter and the seat face flatness together — a round bore against a tilted seat rocks the driver and changes the acoustic volume behind it. In practice:
- Bore: ±0.01–0.02 mm
- Seat face flatness: 0.02 mm
- Surface finish: Ra 0.8–1.6 μm
2. Nozzle bore and mesh seat
The nozzle is the tightest feature on the part. A typical bore runs Ø3–6 mm with a concentricity requirement to the driver seat of 0.02–0.03 mm. Below that, the sound signature shifts between units because the front cavity volume changes.
Ask for the nozzle to be machined in the same setup as the driver seat wherever geometry allows. That single decision removes a whole datum transfer from the tolerance stack.
3. Lid or faceplate interface
Threaded lids on metal housings usually run M6×0.5 to M10×0.5 fine pitch. Two rules:
- Specify the thread after anodizing, or mask it. A 10 μm anodize layer changes the effective fit of a 0.5 mm pitch thread enough to cause cross-threading.
- Run the thread with a rolled tap, not a cut tap, and deburr the entry.
4. Cable entry and strain relief
The strain relief bore sees the highest real-world load on the entire housing. Give it a generous radius at the exit — a sharp edge here is the most common field failure we see on returned parts.
Tolerance reasoning across all four is covered in CNC machining tolerance.
Wall Thickness and Weight
In-ear housings typically run 0.6–1.0 mm walls; over-ear cups run 1.0–1.5 mm. Below 0.6 mm in aluminium, the part becomes a fixturing problem: it will chatter under the tool unless the fixture supports the wall directly, and cycle time rises sharply.
Two design moves that help:
- Vary the wall. Keep 1.0 mm at the strain relief and thread, drop to 0.7 mm over the acoustic cavity where nothing is loaded.
- Add a rib instead of thickening the shell. A 0.6 mm wall with a 1.0 mm rib around the driver seat is stiffer and lighter than a uniform 1.0 mm wall.
More of these moves are in our DFM analysis guide.
Finish: What Buyers Actually Specify
| Requirement | Specification to write on the drawing |
|---|---|
| Colour consistency | Anodize Type II, 10–15 μm, ΔE ≤ 1.5 against approved master |
| Scratch resistance | Anodize Type III (hard coat), 25–40 μm |
| Soft tactile feel | Sandblast #180–220 then Type II |
| Directional grain | Brush, Ra 0.4–0.8 μm, grain direction indicated |
| Logo | Laser mark (etch depth 0.02–0.05 mm) or silk screen |
| Thread / bore protection | "Mask M8×0.5 thread and Ø4 nozzle bore prior to anodize" |
The single most common dispute in audio housing supply is colour. Solve it before production by approving a physical master sample and putting a ΔE tolerance on the drawing rather than a Pantone reference alone — anodize dyes do not map cleanly to Pantone.
Our anodizing guide covers film growth and thread compensation in detail.
Volume, Cost and Lead Time
| Stage | Typical quantity | Lead time | Notes |
|---|---|---|---|
| Concept sample | 1–5 | 5–7 days | Machined, may skip finish |
| Design validation | 20–50 | 7–12 days | Full finish, dimensional report |
| Pre-production | 200–500 | 12–18 days | Production fixture, first-article CMM |
| Production | 1,000+ | 15–25 days | Fixtures amortised, unit price stabilises |
The largest single cost lever is number of setups. A housing that needs four operations (turn, mill front, mill back, thread) costs materially more than one that can be done in two on a mill-turn platform. Designing the part so that the nozzle, driver seat and thread share one axis is usually worth more than any material substitution.
Budgeting detail is in CNC machining cost drivers, and supplier qualification is covered in how to choose a CNC supplier.
What to Put in the RFQ
- STEP model plus a dimensioned 2D drawing (PDF)
- Alloy and temper, with acceptable alternatives
- Finish specification including film thickness and ΔE target
- Which features must be masked
- First-order quantity and projected annual volume
- Inspection requirement: first-article CMM, 100% thread GO/NO-GO, or AQL sampling
Six items, and a quote comes back in 24 hours with DFM feedback.
Getting Started
Earphone metal housing CNC machining rewards early decisions more than late ones: pick the alloy for its anodize behaviour, align the nozzle and driver seat on one axis, mask the thread before you finish, and approve a physical colour master. Do those four things and the housing stops being the part that holds up the launch.
Ruijin Fenghui Precision Technology machines audio components in Dongguan with 200+ CNC centres, in-house anodizing, brushing, sandblasting and laser marking, under ISO 9001:2015 with 23+ years of precision machining. Prototype housings in 3–7 days; quotes with DFM feedback in 24 hours.
Related: microphone metal parts, audio knobs, speaker CNC parts, brushed aluminium panels, rapid prototyping, stainless steel parts, material selection.