"Acoustic power emissions: 6.6 B(A)." "51 dB(A)." Both lines come from spec sheets for the same HP printer, and no shifting of a decimal point turns one into the other.
The first is sound power, everything the machine gives off. The second is sound pressure, the part that reaches one spot. Printer and computer spec sheets print both, and the two look like relatives when they are not. The printer and mini PC guides lean on this distinction all the time, so here it is explained once, using only figures the makers publish.
What is sound power level?
The total acoustic energy a machine emits, in every direction, wherever it sits and wherever you stand. It belongs to the machine the way wattage does. Declaration standards write it A-weighted in bels, B(A), and one bel is ten decibels.
HP declares the LaserJet MFP M234dw at "Acoustic power emissions: 6.6 B(A)". Dell's idle declaration for the OptiPlex Micro 7020 is 2.7 bels. The Mac mini comes in at 1.3 B.
Because no microphone position is involved, these numbers can be compared with one another. Apple, Dell, HP and Lenovo declare their computers this way, under ISO 7779 and ISO 9296, and that is what the laptop and desktop PC guides compare.
They cannot be compared with anything in dB(A) at a distance. That is the other quantity.
Sound pressure belongs to a place
It is whatever arrives at one point: a microphone a metre away, or the operator position, which is the standards' term for where a person sits. Written in dB(A), it follows what reaches your ears more closely than anything else on the sheet.
Xerox lists the B230 under "1-meter Average Sound Pressure, dBA": 53 printing one-sided, 16 in ready. Dell's idle figure is 15.4 dB at the operator position, with a separate column for the bystander, and Apple publishes 4 dB at the operator position for the Mac mini. Each states a position, so each can be compared.
The decibel chart leaves sound power out for this reason. Set beside a whisper or a fridge, a power figure would land in the wrong place.
In a proper declaration the two travel together. HP's international datasheet for the M234dw carries 6.6 B(A) of power and 51 dB(A) of pressure. You cannot get from one to the other without knowing the room and the distance, and that is why the standards ask for the pair.
One bel is ten decibels
This is where spec sheets trip people up.
A sound power declaration of 6.6 B(A) works out, numerically, to 66 dB of sound power. Next to a 51 dB(A) pressure reading, it seems to disagree with itself by 15 dB. It does not. The two numbers measure different things, and the 66 was never a pressure anyone would hear.
Canon sets the trap from the other side by writing sound power in decibels. Its MF275dw specification gives "Sound Power" as "Active: 69.3 dB or less". Beside HP's "6.2 B(A)" that reads like a machine three times as loud, yet it is 6.93 B, right where a small laser printer belongs. Read the row label, then the number.
Hard drives show both habits. Seagate's product manuals print sound power in bels, while WD marks its Blue figures in dBA as sound power, as the hard drive guide records.
Power tools sold in Europe print the pair in decibels under labels of their own. On Milwaukee's European page, the M18 FPS55 plunge saw lists "Sound pressure level (Lpa)" 92.4 dB(A) and "Sound power level (Lwa)" 103.4 dB(A), each with an uncertainty of 3. The circular saw guide quotes the figure at the ear and the sound power figure separately for every saw that declares them.
KV and the ISO standards on a spec sheet
KV is a statistical adder carried by declared tables. Dell's OptiPlex declaration reads 2.7 bels with "KV, (bels)" of 0.4; the Mac mini reads "1.3 (KV = 0.3)". Add the two and you have what ISO 9296 calls the value for verification, the level a sampled unit should not exceed.
A maker that prints its KV is showing its working. In our guides, that maker outranks one printing a bare number at the same level.
The standards named beside a figure say how it was measured and declared. ISO 7779 covers measuring, ISO 9296 and ECMA-109 cover declaring, and ECMA-74 sets the operating modes, idle against disk against processor load. A figure that names any of them is worth more than the same digits naming none.
Who labels which quantity
Computer makers label both quantities almost every time; printer and hard drive makers often leave the quantity out. We sorted 110 products in six catalogs by what the maker declares, as listed on October 26, 2026. Other models may differ.
| Catalog | Products | Both quantities declared | One quantity, labelled | Quantity not stated | No figure |
|---|---|---|---|---|---|
| Laptops | 20 | 20 | 0 | 0 | 0 |
| Desktop PCs | 19 | 19 | 0 | 0 | 0 |
| Gaming laptops | 14 | 10 | 4 | 0 | 0 |
| Mini PCs | 20 | 7 | 0 | 11 | 2 |
| Printers | 22 | 12 | 1 | 9 | 0 |
| Hard drives | 15 | 0 | 7 | 8 | 0 |
| All six | 110 | 68 | 12 | 28 | 2 |
Labelled means the maker's wording says sound power, sound pressure, LWA, LpA, bels or operator position. Quantity not stated means a bare dB or dBA figure with none of those words, and we never rank one of those against a declaration.
Computers usually carry full declarations
Every laptop and desktop in our catalog from Apple, Dell, HP and Lenovo is declared with both quantities and a named standard. The 7 mini PCs that match them come from the same four makers.
The 11 mini PCs with no stated quantity are from Minisforum, GEEKOM and Beelink. Minisforum at least gives a distance, "30 dB @ 50cm" for the MS-01 SE at idle, while Beelink prints "32dB" on every current model. Zotac and ASUS publish nothing for their fanless models.
The 4 gaming laptops with a single labelled quantity are ASUS and MSI models declared on European ErP Lot 3 sheets, which give sound power alone.
Printers and hard drives often drop the label
The HL-L2400D gets "Machine Noise" of 30dB ready and 48dB printing from Brother, with no word on which quantity that is. Lexmark and Canon's PIXMA G3270 do the same, making 9 of the 22 printers.
Hard drives are worse. WD's Red and Purple data sheets head the row "Acoustics (dBA)" and the Gold sheet "Acoustics (average)", naming no quantity, while the Blue sheet adds a footnote reading "Sound power level." Toshiba's sales sheets print "Acoustics Idle Mode [dB]" without saying which. Seagate's product manuals are the clearest of the lot, with "Drive acoustics, sound power" in bels.
The IronWolf 4TB shows what a missing label costs you. Seagate's data sheet gives 23 dBA idle and 27 dBA seek, unlabelled; the product manual gives 2.3 bels idle and 2.5 bels seek, labelled sound power. The idle digits match and the seek digits do not, and Seagate never says whether the two sheets measure the same thing.
Sound power written in decibels
Nine of the 79 products that label a sound power figure print it in decibels rather than bels. Canon writes "69.3 dB or less" for two printers and 66 dB for a third. ASUS gives the ROG Zephyrus G14 24.1 dB, and WD Blue prints 23 dBA under its sound power footnote.
MSI's column heading on the Stealth 16 AI is "Bels / dB", sitting over figures of 23.2 and 44.6 that only work as decibels. Each of these numbers is ten times what the same figure would read in bels.
Can you convert sound power to sound pressure?
Not from a spec sheet. The conversion needs the distance, the room and the way the machine radiates sound, and declarations give none of those. The makers' own pairs show how loosely the two numbers are tied.
Turn each bel figure into decibels and set it beside the same machine's pressure figure while printing. For the 12 printers in our catalog that declare both, the gap runs from 7 dB to about 19 dB. HP's OfficeJet Pro 9125e, at 6.8 B(A) and 61 dB(A) printing at 20 ppm, is at the narrow end; Canon's MF275dw, at 69.3 dB of sound power and 50 dB of sound pressure printing one-sided, is at the wide end; Epson's four EcoTank and WorkForce models fall between, at 11 to 14 dB.
With a gap that moves by 12 dB inside one product type, no rule of thumb can turn a power figure into what you will hear. Compare power with power, and pressure with pressure.
How do you read a declared noise emission table?
Four things to find: the quantity, the operating mode, the standard and the margin. Work through them in order.
- Find the column heading and note whether it says sound power (LWA, in bels) or sound pressure (LpA, in dB).
- Read across to the operating mode, such as idle, disk access or CPU load.
- Check which standard the table names, usually ISO 9296, ISO 7779 or ECMA-109.
- Look for KV or an upper-limit label, which tells you whether the margin is included.
- Compare the figure only with the same quantity and mode on another declaration.
A Lenovo ThinkPad declaration, line by line
Lenovo's ECO Declaration for the ThinkPad T14s Gen 7 is "Declared according to ISO 9296". The sound power row is a "Statistical upper limit" of 2.5 B at idle, 3.2 B with the drive working and 3.4 B under CPU load.
At the operator position, pressure reads 15.8 dB idle, 25.1 dB with the drive working and 26.7 dB under CPU load. From idle to CPU load the pressure figure climbs about 11 dB, the power figure 0.9 B, or 9 dB.
Which row to use depends on the question. The CPU-load pressure figure is closest to what you will hear at your desk in a demanding moment, while the power figures for one mode are the fairer test against another ThinkPad. The laptop guide quotes both for each machine.
How our tables handle the two quantities
Every figure says which quantity it is, in the unit the maker printed. A power figure is never ranked against a pressure figure, and neither is ranked against a bare marketing number like that "32dB". Where a maker publishes both, the pick's noise line carries both. A declared figure under ISO 9296 or ECMA-109 comes with a method, a load state and an adder, which is why a marketing number cannot sit in the same ranking as a declaration; that page also explains where one brand's figure breaks down against another's.
Sones are a third thing again, a perceptual loudness scale used for bathroom fans and range hoods, with a page of their own.
