When a machine has to meet a noise figure, the cabinet around it becomes part of the acoustic design. The metalwork’s contribution is narrower than most people expect — and getting that narrow part right matters more than anything else.
Four Different Jobs, Often Confused With One
Mass resists airborne sound passing through a wall. Damping stops a flat panel ringing after it is struck. Absorption reduces reflections inside the cavity. Sealing removes the shortcuts sound takes around the barriers. Sheet metal work mainly delivers mass, sealing, and the surfaces that any absorbing layer mounts onto. The other two are material decisions that sit above us, and pretending otherwise is how cabinets end up heavy, expensive and still loud.
Why a Gap Beats a Thin Wall
Air paths dominate a noise budget. A continuous slot at a door seam, an unsealed cable entry or a ventilation opening can leak more sound than an entire panel transmits. This is also why adding material thickness so often disappoints: if the openings are still open, doubling the wall buys very little. Worth covering the relationship early, because it determines whether the budget should go into thicker panels or into better joint design — usually the second.
Welded Versus Bolted Construction for Quiet Enclosures
Welded construction gives a continuous barrier and a very rigid shell, which helps panels behave. It also produces a single large object that can be awkward to ship, awkward to get through a doorway, and expensive to replace when one side is damaged.
Bolted or modular construction ships flat, goes together on site, and lets a damaged panel be replaced instead of scrapped — but every joint is now a potential leak, so joint design moves into the critical path: a continuous gasket land, bolt spacing that actually compresses the gasket evenly, and stiffened edges that do not bow between fixings. Units that have to be split for transport weight almost always end up modular for this reason alone.
Panel Resonance and Where Stiffening Helps
A large flat panel behaves like a drum skin and radiates efficiently at its own resonant frequency. Beads, stiffeners and doublers raise that frequency and reduce the amplitude; changing panel size or adding an asymmetric stiffening pattern avoids several panels all ringing at the same pitch. This is usually cheaper than adding thickness, and it is the one acoustic contribution the metalwork alone can make without adding material cost.
Who Supplies the Absorbing Layer
Mineral wool, PU foam and composite absorbers carry decisions about fire behaviour, ageing, hygiene and disposal that belong to the finished machine, not to the cabinet we build. In practice the equipment maker specifies the material and its facing; we build the structure to drawing and can fit the layer when it comes with a defined material, thickness, facing and fixing method. Two things need settling before quoting: whether that layer is inside our scope at all, and how it changes the assembly sequence — lining generally has to go in before the panels close, which affects how seams and access panels are designed.
How the Result Gets Verified
Noise performance is measured on the assembled machine, by the equipment maker, by their customer, or by an independent testing laboratory — under conditions that include the source, the room and the measurement positions. Our scope is the enclosure metalwork built to drawing and to the agreed general tolerances, see the tolerance guide for OEM projects. We do not state or certify measured sound levels for a machine we did not build, and any supplier who does should be asked how the figure was obtained.
What To Send for a Quiet Enclosure Quote
The target figure on your specification and the conditions it has to be met under, drawings or at least a layout, where the noise source sits inside the enclosure, the airflow the machine needs (ventilation is usually the single hardest constraint), the access required for service, whether the absorbing layer is in your scope or ours, and any shipping limits that force a modular design. For the finishing side of outdoor units, galvanised versus powder-coated options and industrial coating standards cover the corrosion questions; outdoor unit casings and machine covers and guards are close neighbours structurally.
Questions We Get Asked About Enclosure Noise
Will a thicker panel make the enclosure quiet enough?
Often not by itself. Thickness helps where transmission through the wall is the dominant path; once openings and seams leak, extra mass returns very little for its cost. Decide between ‘more panel’ and ‘better sealing’ before specifying steel gauge.
Do you supply cabinets with acoustic lining already fitted?
We can fit a lining when its material, thickness, facing and fixing method are specified on your drawing. Absorber selection itself belongs to the equipment maker, because fire behaviour, ageing and hygiene requirements are assessed for the finished machine.
Is a bolted enclosure worse than a welded one acoustically?
Not inherently. Welded is continuous and avoids joint design errors; bolted, when designed with a proper gasket land, correct fixing spacing and stiffened edges, performs just as well and is far easier to ship and service. The failures we see come from bolted seams that were designed structurally and never checked acoustically.
Can you give us a measured dB figure for the enclosure?
No. Sound measurement belongs to the assembled machine and is carried out by the equipment maker or an independent laboratory. We build the enclosure metalwork to drawing and to agreed general tolerances.
What the Metalwork Can and Cannot Do About Noise
An enclosure’s contribution to a noise figure is narrower than most people expect, and knowing the boundary saves money. The metalwork does three things: it provides mass, which resists airborne sound passing through a panel; it provides a continuous barrier with no gaps, which matters more than mass because sound takes the easiest path; and it provides stiffness, which stops panels from resonating and turning into speakers. What it does not do is absorb. Absorption comes from a layer that is added inside, and that layer is a separate supply.
- A gap is far worse than a thin panel. An unsealed cable entry or a poorly compressed door will leak more sound than a thicker panel would ever stop.
- Stiffening a large flat panel moves its resonant frequency away from the frequency being generated, which is often the cheapest single improvement available.
- Welded construction is quieter than bolted construction for the same panel thickness, because a bolted joint can move and a welded one cannot.
How the Result Gets Verified, and by Whom
A noise figure is a property of the finished machine in its installed condition, not of the cabinet. The enclosure is built to the design intent – panel thickness, stiffening layout, sealing method, and the provisions for the absorbing layer – and the measurement that produces the number is carried out on the assembled equipment, by the equipment manufacturer or a third-party test house. A cabinet cannot be certified quiet on its own.
What we can do is remove the variables that are ours: hold the panel flatness so gaskets seal, place the stiffening where the drawing says, and keep the apertures to the positions specified, because every aperture is both a leak path and a place a panel loses stiffness. Send us the panel sizes, the target frequency range if you know it, and how the absorbing layer will be fitted, and the enclosure design follows. Lead time is quoted after drawing review and process confirmation.
What stands behind this quotation
- Manufacturing since 20162,500 m² Ningbo plant — 3 laser cutting machines (including newer TRUMPF), 4 CNC press brakes and 10 welding stations.
- Shipped to more than 30 export marketsEnclosures, cabinets and formed parts supplied to OEM buyers across Europe, North America and Asia.
- 123 documented product casesMedical device housings, HVAC and heat pump enclosures, agricultural and livestock equipment, industrial hydraulics, material handling trolleys and EV charging cabinets.
- Factory evidence you can checkTUV Rheinland audit reference MIC-ASI243729 and Bureau Veritas reference MIC-ASR263630 available for buyer review under NDA.
Before you send drawings: an NDA is signed on request · first-article inspection is carried out before a batch continues · pricing is staged from prototype quantity to repeat volume · pre-shipment photos and packing records are prepared when the project needs them.