Most air cushion machine noise disputes are not really arguments about a blower. They are arguments about a number that was measured in a condition nobody on the project will ever experience, and then compared against a limit that was set for a completely different machine.

A Decibel Target Is a Measurement Condition, Not a Product Attribute

Decibels are logarithmic, and that causes most of the confusion. A 3 dB increase doubles the acoustic power, and 10 dB is roughly what listeners experience as a doubling of loudness. A blower moving from 68 dBA at free air to 56 dBA at blocked outlet radiates roughly a sixteenth of the acoustic power, not marginally less.

The harder problem is that a decibel figure only means something when it carries its conditions. Distance, mounting, load state, frequency weighting and ambient level all change the result. A level measured one meter from an unrestrained blower cannot be compared with one measured inside a steel-framed machine at a working duty point.

This is why ISO 13347 is a family rather than a single document. ISO 13347-4:2025 specifies sound power measurement by sound intensity on a surface enclosing the source, and requires the acoustical environment, ambient noise and measurement surface to be defined. ISO 13347-3:2026 covers the enveloping surface method and is explicit that it determines airborne sound emission only, not vibration. The method and the condition are part of the number.

So before comparing any published figure with a 65 dB warehouse limit, settle four things: measurement distance, load state, frequency weighting, and the ambient level in the room where the machine will run.

What Two Published Blowers Actually Measure

Two of our published units carry a noise figure, and they make the point better than any argument could. Both numbers are taken from our own product pages, and in each case the figure depends on the condition the blower is running in.

Read the first column of data rather than the headline. The WS7040AL spans 56 dBA to 68 dBA depending on what it is doing, and the WS9250 spans 67 dBA to 83 dBA. Neither unit has a single noise characteristic, because noise is a function of how hard the impeller is working, not a fixed property of the part.

Two consequences follow for a 65 dB warehouse limit. First, the WS7040AL can sit inside that limit at some duties and outside it at others, so the duty decides whether the unit is acceptable, not the catalogue. Second, the WS9250 does not reach 65 dBA in any published condition, so specifying it against that limit is specifying a failure before the first sample arrives.

Note also what our low noise air cushion blower range does and does not publish. Performance figures, airflow, pressure, speed, current and tolerance are all published on the product pages. A single decibel number is not, because there is no single decibel number to publish.

Where the Sound Comes From and Why Each Path Differs

Blower noise reaches an operator by three routes, and each responds to a different fix.

Broadband aerodynamic noise is the rush of the air itself. It rises steeply with shaft speed, which makes the speed setting the most effective lever on this component. Reducing commanded speed costs duty, so size for the duty and run at the speed it needs.

Tonal noise is a set of discrete tones: blade passing frequency, bearing frequencies, and their harmonics. These do not fade when you slow the blower down, because they are a symptom of rotor imbalance. ISO 21940-11:2016 is the reference for residual unbalance tolerance and correction planes on rotors with rigid behavior, and it is what to ask a supplier about rotor balance.

Structural noise is what makes a machine loud rather than a blower loud. It leaves the casing as vibration, travels through the mounting bracket, the frame and the ductwork, and re-radiates from those surfaces. Isolation solves this path and no other.

That is where most advice goes wrong. Our own published answer on the low noise brushless blower product page is to fill between the blower and the machine with foam or silicone. It works, and it works on structural noise only. The inlet and the outlet remain open radiators, so broadband noise still reaches the operator at the level the duty produces.

Why 65 dB Is a Machine Target and Not a Blower Target

A warehouse limit is written for the place, not for the part. It describes what a person at a workstation is exposed to, and it is reached by everything the machine contributes at once: the blower, the cushion film bursting and settling, the plenum and ductwork, the frame resonating, and the shop floor.

Two practical points follow, and both change what you should ask a supplier for.

The first is that the ambient level sets the floor. If the packing hall already runs at 62 dBA, a blower reading 63 dBA at the operator position is not a noise problem, and no acoustic work on the machine will change that. If the hall runs at 55 dBA, the same blower is a clear problem.

The second is that the measurement position matters as much as the number. A meter at the blower inlet, at the machine guard, and at the operator position gives three different readings for the same running machine. Which one your customer cares about determines which one you should be quoted against, and that is a question to settle before the blower is chosen.

Noise reduction is therefore not a blower selection exercise. It is a sequence, and the order of that sequence decides whether the target is met on the first attempt or after a costly retrofit.

How to Get a Noise Figure You Can Put in a Purchase Order

1. Write down the limit in a form that can be measured. State the position, the frequency weighting, the load state and the ambient level. A target that says only 65 dB cannot be tested, so it cannot be enforced and will be settled by opinion.
2. Ask for the noise data as a set, not as a single number. Request the figure for the free air condition, the rated working point and the blocked outlet, with the test method named. A single number with no condition attached cannot be compared with anything.
3. Ask which standard the test follows. ISO 13347-2:2025 covers the reverberant room method for fan sound power, and other parts of the family cover enveloping surface and sound intensity. Naming the method makes the figure reproducible and comparable with one from another supplier.
4. Separate the three noise paths in the test plan. A broadband reading with the inlet and outlet open tells you about airflow noise; an isolated reading tells you about structural transmission. Without that separation you cannot tell whether the fix belongs on the rotor, the speed, or the mounting.
5. Specify the isolation treatment in the same document as the blower. Foam or silicone between the blower and the machine is our own published recommendation, but it belongs to the machine builder, not the blower supplier, and must be written into the purchase order rather than assumed on site.
6. Order one sample and measure it on your own line before the production order. Our standard minimum order quantity is one piece, and samples can be ordered for testing before a larger order. Measuring the actual unit on the actual machine at the actual position is the only step that converts a specification into a verified result.

What Still Has to Be Settled After the Blower Is Chosen

Choosing a blower that can meet the target is the easy half. Several things remain open afterwards, and each can move the result by more than any change of blower model.

Duty cycle. A cushion machine inflates in bursts and then idles. If the blower runs continuously because the machine needs it to hold pressure, the noise exposure at the workstation is continuous rather than intermittent, and the average level matters more than the peak.

Acoustic treatment of the machine. Soft material on the frame, lined ductwork and a lined plenum change how much sound the structure re-radiates. This is the treatment that the published foam and silicone recommendation belongs to, and it is worth doing before the machine is built rather than after it fails a test.

Inlet and outlet configuration. A blower discharging into a short open tube is not the same acoustic source as the same blower in a lined duct of the same length, and neither is the same as a blower behind a plenum with a silencer. The published figures assume a laboratory arrangement, so the machine configuration has to be specified alongside them.

Service and contamination. A blocked or dirty inlet changes the operating point, and with it the noise. Published guidance on these units is to fit a filter to the inlet and keep the ambient temperature low.

Questions Buyers Ask About Blower Noise

Send Your Noise Target and Get the Condition Behind the Number

Tell us the limit, the measurement position, the duty the machine runs at and the ambient level in the space, and we will send the published noise figures for the blower families that suit that duty, with the condition attached to each one, and say plainly which of them land inside your limit.

Send the bore and voltage, the airflow and pressure the cushion needs, the duty cycle, and the noise limit with its measurement conditions, and the sales team will come back with the matching units and their noise data.

Last verified: 2026-11-05. The sound pressure levels of 68 dBA at free air, 64 dBA at maximum air pressure and 56 dBA at blocked outlet for the WS7040AL-12-X200, and 83 dBA at free air with 67 dBA at blocked outlet for the WS9250-12-240-S200, are as published on those product pages. Measurement distance, mounting, weighting and ambient level are not published and should be requested with the data. Machine, ducting and cushion noise and the result at the operator position are engineering determinations that depend on the installation.