Audio: An Extruded Speaker Enclosure With Consistent Wall Thickness
In an audio enclosure, the wall is part of the instrument. When wall thickness varies along a cabinet, the cabinet resonates differently from unit to unit — and the customer hears it before they can measure it.
- Industry
- Audio
- Process
- Extrusion + CNC + bead blast or brush finish
- Alloy
- 6063-T5
- Key spec
- Wall uniformity ±0.02 mm
What the customer needed
The customer was building a speaker cabinet from an extruded aluminum body. Aluminum was chosen for stiffness and for the industrial look, and the body was to be one extrusion with machined baffle faces at each end.
The constraint was wall thickness uniformity: ±0.02 mm. In a sealed cabinet, the wall is a vibrating surface. If the thickness changes along the length, different zones resonate at different frequencies, and two units from the same batch stop sounding identical.
The second constraint was internal geometry: ribs and mounting pads had to be formed in the profile, because adding them later would mean machining inside a closed box.
Constraints that decided the part
- Wall thickness uniformity ±0.02 mm along the length
- Internal ribs and pads formed in the profile
- Baffle faces machined flat for a seal
- Alloy 6063-T5 for extrusion quality and finish
- Finish chosen for acoustics and appearance
How the part was made
The same route we would propose today, in the order it actually runs.
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Section design with internal geometry
The wall, ribs, mounting pads and baffle step were laid out in one section. Internal features formed in the die are the only way to get structure inside a closed cabinet.
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Die and extrusion
The die was cut in 4–5 days with bearing length controlled along the section, and the profile was run and aged to T5. Wall thickness is a die and pulling-tension result, not something machining can correct afterwards.
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Machining the ends only
Baffle faces machined flat and perpendicular to the axis, plus mounting holes and port cut-outs. The internal surfaces stay as extruded, because they cannot be reached.
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Finish selection
Bead blast for a matte that stays uniform on a large flat face; brushing where a directional grain suits the design. Both are approved on a chip.
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Inspection
Wall thickness checked at several points along the length, then an acoustic sample check by the customer on the assembled cabinet.
The numbers the part had to hold
These are the tolerances and process values that governed the job. They come from our capability, not from a customer specification we cannot publish.
| Parameter | Value | Why it mattered |
|---|---|---|
| Wall thickness uniformity | ±0.02 mm | Variation along the wall shifts resonance between units |
| Profile cross-section | ±0.05 mm | Section accuracy drives the blank for machining |
| Internal ribs | Formed in the die | Structure inside a closed cabinet cannot be machined in |
| Baffle face | Machined flat | The seal depends on a flat, perpendicular face |
| Alloy | 6063-T5 | Extrudes complex sections and finishes evenly |
| Finish | Bead blast or brushing + anodize | Texture choice follows the acoustic and visual design |
The part of this job that nearly went wrong
This is the section worth reading. Every program has one problem that decides whether the parts come out right, and it is usually not the one on the drawing.
Wall variation along a long section
Wall thickness in extrusion is set by the die and by how the profile is pulled. On a long, large section the wall can thin in the middle of a face while measuring correctly at the ends.
The risk
Two cabinets from the same batch that do not sound the same — a defect no dimensional drawing catches and no customer accepts as normal.
What we changed
Bearing length was controlled along the section and the wall is measured at several points along the length rather than at one cross-section. The measurement is reported so the customer can correlate it with their acoustic test.
Structure inside a closed box
Ribs and mounting pads inside a cabinet cannot be machined after extrusion — a cutter cannot reach them through the baffle opening. If they are not in the profile, they do not exist.
The risk
A cabinet that needs a secondary welded or bonded structure, which reintroduces the seams and the cost the extrusion was meant to remove.
What we changed
All internal geometry was designed into the section at the die stage: ribs for stiffness, pads for the crossover board and screw bosses for the baffle. Nothing inside the cabinet requires a second operation.
A cabinet that sounds the same on unit 1 and unit 500
The enclosure is a single 6063-T5 extrusion with a wall thickness capability of ±0.02 mm, internal ribs formed in the die and baffle faces machined flat and perpendicular. Machining is limited to the ends and the port cut-outs.
Because the internal structure comes out of the die, there is no welded or bonded sub-assembly inside the cabinet and no seam to seal. The finish — bead blast or brushing — is chosen for the design and approved on a chip.
The acoustic result is verified on the customer's bench, not in our inspection report. What we control is the wall consistency that makes the acoustic result repeatable.
Common questions about this program
The questions this case generates from engineers and sourcing teams.
Why does wall thickness matter acoustically?
In a sealed cabinet the wall is a vibrating surface. Its stiffness depends on thickness, so a wall that varies along the length resonates differently at different points. Uniform wall means the cabinet behaves consistently, and two units sound the same.
Can you machine features inside the enclosure?
Generally no — a cutter cannot reach inside a closed section through the baffle opening. Internal ribs, pads and bosses are formed in the die at the section design stage, which is why we ask for the internal layout before quoting.
Bead blast or brushing for a speaker cabinet?
Bead blast gives a uniform matte that stays consistent across a large face and hides handling marks. Brushing gives a directional grain that suits some designs but must be specified per face, because the grain direction becomes part of the look.
Building a Cabinet Where the Wall Is Part of the Sound?
Send the section and the internal layout. The ribs and pads have to be in the die, and that decision is much cheaper before tooling than after.
What to send
- 2D drawing or 3D model (STEP, IGES, DWG, DXF, PDF)
- Alloy and temper
- Surface finish and color
- Estimated annual quantity
Client names are withheld under confidentiality. Figures reflect our verified process capability.