How quiet is quiet
Every listing claims to be quiet and almost none of them publish a number. When they do, it is measured at a metre in a still room on the lowest setting — three conditions that are all wrong for how you will actually use it.
What actually makes the noise
In rough order of contribution:
The motor. Brushed DC motors — what almost everything at the lower end uses — have carbon brushes running on a commutator, and that contact is inherently noisy. Brushless motors are quieter and smoother and cost more. This is the single largest factor and it is not something you can inspect from a listing.
How the motor is mounted. A motor rigidly fixed to a hard shell transmits every vibration into that shell, and the shell radiates it as sound. A motor suspended in a soft mount, or potted in silicone, decouples it. Two devices with identical motors can differ by 10 decibels on this alone. This is also invisible from a listing, which is why the price is a weak signal and the reviews are a better one.
The shell. Thin walls resonate. This is why small, cheap bullets can be disproportionately loud for their size — there is very little material to absorb anything.
What it is resting on. A bedside table is a soundboard. The same device on a folded towel is measurably quieter than the same device on wood, because the table is being driven like a speaker cone.
The number is measured where you are not
A figure quoted at one metre is the standard convention, and it is the wrong distance for this product.
Sound falls off by roughly 6 decibels for every doubling of distance in an open room. Your hand, or the bed, is not a metre away — it is closer to 20 or 30 centimetres. Moving from a metre to 30 centimetres is about a tenfold change in distance, which is worth roughly 10 decibels.
So a device measured at 45 dB at one metre is around 55 dB at the distance you will actually hear it. That is the difference between a library and a conversation.
Add a tiled bathroom, where sound bounces instead of being absorbed, and the same device is louder again.
The scale, in things you know
Decibels are logarithmic, so they do not add up the way ordinary numbers do. An increase of 10 is roughly twice as loud to a listener. That means the gap between a 40 dB device and a 50 dB device is not "ten units" — it is the difference between something you can barely hear through a door and something you can.
This is why "quiet" is such a useless word in a review. Somebody writing "very quiet" may be comparing it to a vacuum cleaner.
Pitch matters more than volume
At the same measured level, a high-pitched sound is more noticeable and more irritating than a low one, and it carries through walls and floors better.
This is why a small bullet at 45 dB can be more intrusive than a larger device at 50 dB. The larger one has more mass, which lowers the frequency, and low frequency is absorbed by walls rather than passing through them.
If your concern is being heard through a wall rather than being heard in the room, pitch is the thing to care about, and it is the thing no listing tells you.
What you can do about it without buying anything
- Put something soft underneath. A folded towel decouples the device from the furniture, which is often the biggest single improvement available.
- Get off hard surfaces. Tiles, wood and glass all reflect and transmit.
- Turn it down. Noise scales with motor speed, so the top setting is always the loudest.
- Keep a hand on it. Contact with your hand damps the shell. This is not a joke — the mass and the damping are real.
- Charge it. A cell that is nearly flat makes some motors labour, which is rougher and louder than the same motor at full voltage.
Reading a listing for noise
There is almost nothing reliable, so the approach is indirect:
- Look for a published figure with its conditions. "Under 50 dB at 1 m" is at least checkable. "Whisper quiet" is not a claim, it is a mood.
- Search the reviews for the word noise, loud, or vibrate. People describe noise comparatively and honestly, in a way they do not describe anything else.
- Look at what the device is made of. A thick silicone body over a potted motor is the configuration that is quiet. A hard plastic shell with a visible seam is the configuration that is not.
- Distrust the size assumption. Bigger is not automatically louder, and small is not automatically discreet.
Questions that come up
Is a wand louder than a bullet?
Usually louder in absolute terms, but lower in pitch, which is why it is often less audible through a wall. Which one is more discreet depends on what you are worried about.
Does a quieter device cost more?
Correlated, not reliable. The motor mount is the expensive part and it is the part nobody advertises, so price is a weak proxy.
Will a blanket over it help?
A blanket under it helps a lot. A blanket over it helps less and traps heat, which is bad for the cell.
Does lubricant make it quieter?
No. But running it dry against skin makes friction noise, which is a different sound and often the one people are actually worried about.
Does the noise get worse over time?
Usually yes, slowly, as bearings wear and mounts take a permanent set. A device that has become noticeably louder than it was is on its way out.
More guides
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