42 dB(A) or 30 dB(A): The Quieter Fan Could Not Do the Job

What the automation OEM needed

An industrial automation OEM needed a cabinet fan on a 24V DC rail, inside 92 by 92 by 25.4 mm. In the end the choice came down to fan noise versus airflow.

They had already picked a model. Consequently their performance targets were visible without being stated.

What the choice implied

• First, airflow of at least 64.94 CFM, targeting 72.16 CFM at free delivery.
• Next, enough pressure to overcome 75 Pa of system impedance.
• Meanwhile an ambient range of -10C to +60C and a 50,000-hour L10 life.
• Noise capped at 45.0 dB(A).
• Finally, UL94V-0 frame and impeller material, non-negotiable for their own UL and CE work.

Notably that last one is a fire retardancy requirement, not a performance one. So it eliminates plenty of otherwise suitable fans before airflow is even checked.

Weighing fan noise versus airflow

Their selection checked out against the P-Q curve. However, the alternative we weighed shows the fan noise versus airflow trade more clearly.

The quieter model, and why it lost

The same 92mm series holds a lower-speed variant at 30.0 dB(A). Notably that is roughly 12 decibels below the chosen fan, which is a large and obvious difference in a room.

However, it moves 43.79 CFM. The application needed 72.16 CFM.

So the quiet model fails on the only thing that actually matters here, which is removing heat. Consequently fan noise versus airflow was settled by the thermal load rather than by preference.

Here the trade is worth understanding rather than negotiating. Airflow in an axial fan comes largely from speed, while noise rises steeply with the same variable. In short, wanting both means changing diameter, not changing model.

Why DC was never in question

The cabinet runs on a native 24V DC bus. An AC fan would need an inverter, which adds cost, volume and a failure point inside an enclosure that is already being cooled.

Bearings decided by the life requirement

A sleeve bearing version exists and costs less. However, the 50,000-hour figure ruled it out.

Sleeve bearings are quiet when new and wear steadily. Furthermore their life drops sharply at high temperature, or when mounted on their side. So two ball bearings gave the longevity and temperature range the spec demanded.

What it cost

Noise, chosen deliberately with the alternative on the table. At 42.0 dB(A) average this fan is audible in a quiet room.

Meanwhile the customer accepted that because a control cabinet is not a quiet room, and because the consequence of the alternative was components running hot. That is the correct order of priorities, though it is worth making the decision consciously rather than by default.

Technical Specifications

Note the bearing row below. That line carries the 50,000-hour figure, and it settled the fan noise versus airflow choice too.

Technical Documentation

LWAD9225MX-24-00 Datasheet: LWAD9225MX-24-00.pdf

Here the document provides complete electrical and mechanical specifications, performance curves (P-Q), and dimensional drawings essential for design engineers and compliance teams integrating the fan.

The product image shows the 7-blade design and standard 92mm frame with mounting holes, confirming the physical form factor for the OEM’s mechanical engineers.

If you are cooling a control cabinet

Cabinet fan selection is a small decision with a long tail. So these are the parts that bite later.

• Settle fan noise versus airflow with a number, not a preference. Work out the heat you must remove and the airflow that requires. Then find the quietest fan that meets it, rather than the quietest fan that fits.
• Do not buy sleeve bearings for anything you cannot reach. They are cheaper and quiet when new. In a sealed cabinet, the wear shows up as noise and then failure, long after anyone remembers which fan was fitted.
• Check the material rating before the performance. UL94V-0 is a hard gate for equipment seeking UL or CE. Filtering on it first avoids shortlisting fans you cannot use.
• Ask for airflow at your impedance, not at free delivery. The headline CFM assumes no resistance. A cabinet with filters and a crowded interior will pull the operating point well back from it.

See our compact fan range, the DC axial fan section, or cabinet cooling fans. Safety testing follows UL 507.

Questions about this fan

Can I get 72 CFM at 30 dB(A)?

Not from a 92mm fan. Airflow at this size comes from speed, while noise rises steeply with it. Instead, moving that much air quietly needs a larger diameter turning slower. So if you have room for a 120mm fan the answer changes. In a fixed 92mm opening, it does not.

When are sleeve bearings acceptable?

When the fan is accessible, runs at moderate temperature, and is mounted with the shaft horizontal. They are quiet, cheap and adequate in consumer equipment. In an industrial cabinet expected to run 50,000 hours without service, ball bearings are the right answer.

What does UL94V-0 actually require?

That the material self-extinguishes within a defined time after a flame is removed, and does not drip flaming particles. It is a material classification rather than a fan test, and it matters because your finished equipment certification will ask for it on parts inside the enclosure.

Why does the 12-26.5V range matter on a 24V fan?

Because real supplies sag and drift. A wide input window means the fan holds its behavior when the rail dips under load or rises on a charged battery, instead of changing speed with the supply. It also lets one part serve a nominal 24V system and a 12V one where reduced airflow is acceptable.