How to Block Out Traffic Noise at Night

By the time traffic reaches your bedroom, the building has already stripped the top off it. That single fact decides which masking sound works and which one is a waste of volume.

What Reaches Your Bedroom Is Not What Is Happening Outside

Stand in the street and traffic is a broad, bright sound: engine, exhaust, tyres on tarmac, the hiss of air. Lie in bed with the window shut and it has become a rumble. Nothing changed outside. The building did it.

Walls, glass and floors are low-pass filters. High frequencies are short-wavelength and lose energy readily as they pass through mass; low frequencies are long-wavelength, carry more momentum through a structure, and get through comparatively intact. So a building removes the top of a sound and lets the bottom past. This is why you hear your neighbour's bass line and not their melody, and it is why traffic indoors is a rumble rather than a hiss.

That single fact settles the colour question. Whatever the spectrum of the traffic in the street, the version that arrives in your bedroom is weighted heavily toward the low frequencies. Masking only works where the masker and the intrusion share a frequency region, so the sound you want is the one with its energy stacked at the bottom: brown noise. White noise puts most of its output far above where the traffic now lives, which is why people try it against traffic, find it does nothing, turn it up, and end up with hiss on top of a rumble.

It also explains a common confusion. Advice written for offices and open-plan spaces recommends white noise, and it is correct there, because the intrusion in an office is speech. Advice written for a bedroom near a road should not say the same thing, and a great deal of it does.

Two Different Noises Are Both Called Traffic

Knowing which one you have tells you how much masking can realistically achieve, which is worth establishing before you spend anything.

Power train noise — engine and exhaust — dominates at low speeds. Pulling away from a junction, a slow residential street, a bus. It is the lowest-frequency part of traffic and it is the part that gets through a building best of all. It is also the part brown noise covers best.

Tyre-road noise takes over above town speeds. Somewhere in the region of thirty to fifty kilometres an hour, depending on the vehicle and the surface, the sound of rubber on tarmac becomes the larger contributor. It is broader in spectrum than engine noise, but by the time it has come through your window the top of it has gone anyway.

Distance turns events into a hum, and that is the easy case. A motorway several hundred metres away produces a continuous low drone with no individual vehicles in it. Continuous sound is the ideal target for masking: the masker only has to sit above a level that never changes, so a modest setting handles it and stays effective all night. If this is your situation, masking will work well.

A road under the window is the hard case. At night, a quiet street with occasional vehicles is not a hum but a series of events, each rising out of near-silence and falling back. Masking handles that poorly, because covering the peak means running the sound far louder than the rest of the night requires, and the abrupt onset is exactly what hearing is built to detect. It still helps. It helps less, and knowing that in advance is better than concluding the technique failed.

Masking Manages the Symptom, Not the Exposure

This section exists because most pages on this subject leave it out, and it changes what you should do.

Masking does not reduce what reaches you. It raises the background so the traffic stops standing out. The traffic arrives exactly as before, and the total sound energy in the room goes up rather than down, because you added a source. That is a fine trade if the aim is to stop being woken. It is not the same as being in a quieter room.

Night-time noise has effects that do not require you to wake up. This is the reason exposure guidance exists at all: disturbance is measured in the body, not in whether you remember anything in the morning. The World Health Organization's Environmental Noise Guidelines for the European Region make a strong recommendation that road traffic noise be kept below 53 dB L_den averaged across the day, evening and night, and below 45 dB L_night specifically to protect sleep.

What to do with that. If you are meaningfully above those levels — and living beside a busy road usually means you are — masking is worth doing tonight, and it is not the whole answer. The measures in the next section reduce what actually arrives, and they are what change the exposure. Many countries also have a route for reporting road noise to a local authority, and mapping data that will tell you what your address is exposed to. Doing both is the sensible position: fix what you can, mask what is left.

Fix the Leaks First — It Costs Less Than Anything Else Here

Sound behaves like water in one useful respect: it takes the easiest path, and one small opening undoes a great deal of solid construction. In most bedrooms the limiting factor is not the wall or even the glass. It is a gap.

Find the air paths. A trickle vent in the window frame, a letterbox, a gap under the door, an unsealed extractor, worn draught seals, a keyhole, cabling coming through a wall. If air moves through it, so does sound, and no amount of mass elsewhere compensates. This is the highest return per pound available in this entire subject and it is usually a weekend and the cost of some seals.

Check the window closes properly. Older casement and sash windows frequently do not seal along their whole length any more. A window that is nominally shut but leaking along one edge is performing far below what its glazing suggests.

Secondary glazing usually beats replacement double glazing for noise. This surprises people. A sealed double-glazed unit has a narrow cavity, sized for thermal performance, and the two panes are coupled closely enough that acoustically they behave somewhat like one. Secondary glazing — an independent internal window with a wide air gap and no rigid connection — is a much better acoustic arrangement, and it is often cheaper than replacing the original window. If you are spending money specifically on noise, spend it here rather than on new units.

Heavy curtains do less than you hope. A thick curtain absorbs some of the high and middle frequencies, which are the ones your wall already removed. Against the low rumble that is actually reaching you it does very little. They are not useless, and they are not the answer.

Move the bed, or move the room. If there is a quieter side of the property, the cheapest fix of all is to sleep on it. Putting the head of the bed on the wall furthest from the road, and putting a wardrobe against the road-facing wall, is free and does more than most purchases.

Setting the Masking Up

Brown noise, through something that can reproduce it. Brown noise puts its energy in the low frequencies, which is the point, and a phone speaker cannot move enough air to produce it. Through a phone you get the thin top and none of the useful part. Use the player above on headphones to confirm the colour is right, then run it overnight on a speaker with a real bass driver or a machine with some size to it.

Set the level against a vehicle passing, not against the gaps. Wait for a lorry, or the loudest thing your road produces regularly, and set the volume so that it stops standing out. A level chosen during a quiet minute will be under-set for every event that follows.

Put the sound near you, not near the window. The instinct is to place the speaker at the source of the problem. Masking does not work that way — the comparison happens at your ear, so what matters is the level there. A source close to the bed achieves the same masking at a much lower absolute level, which means less total sound in the room and less spilling into the rest of the house.

Run it all night. A timer that expires at two in the morning hands the room back to the road at the worst possible hour. Note that a browser tab cannot do this: every website, this one included, is suspended by the operating system when the screen locks. The generator here is for testing whether the colour is right, which takes five minutes. Overnight needs an installed app or a machine.

If brown is not quite covering it, try pink. Some rooms — a thin single-glazed window, a road very close — let more of the top through than usual, and pink reaches further up while still carrying real low-frequency weight. The buttons on the player above switch between them.

What This Will Not Do

It will not help much with sudden single events. A motorbike at one in the morning, a slammed car door, a siren. These rise far above anything a sensible masking level covers, and they are the sounds hearing is most alert to. Continuous masking softens the edge and does not remove them.

It will not reduce your exposure, which is covered above and is the reason the sealing and glazing section comes before this one.

It will not fix vibration. Heavy vehicles on a poor surface can put energy into a building structurally, felt as much as heard. Sound masking has nothing to offer against that, and the answer is the building rather than the air.

It is not a treatment for insomnia. If sleep has been poor for weeks, and quieting the road does not change that, the next step is a clinician rather than a different colour of noise.

If You Only Read One Paragraph

Your walls and windows already removed the high frequencies from the traffic outside, so what reaches the bed is a low rumble — which is why brown noise covers it and white noise does not, whatever advice written for offices says. Before masking anything, find and seal the air paths, because one gap undoes a great deal of solid wall and it is the cheapest fix available; if you are spending on glazing, secondary glazing with a wide air gap beats a replacement sealed unit for noise. Then run brown noise on a speaker that can actually produce low frequencies, set against a passing vehicle rather than a quiet minute, placed near your head rather than near the window, all night rather than on a timer. A distant motorway masks easily. A quiet street with occasional cars is much harder, because masking handles events far worse than it handles a hum.

Frequently Asked Questions

Related pages

• Sound Masking — Masking does not block sound. It raises the floor so the sound stops standing out — and the colour has to match the intrusion.
• Block Neighbour Noise — Bass and footfall need brown noise. Voices through a wall need white or green. Most advice gives one answer to both.
• Block Out Snoring — Snoring is the hardest sound to mask: low, uneven, and a metre from your head with no wall in the way. What actually helps.
• Masking vs Earplugs — Earplugs work least well exactly where household noise is worst. Masking can be aimed. Why the answer is usually both.
• Brown Noise — The deepest colour, measured at −5.98 dB per octave — best for traffic rumble and long overnight sessions.
• Brown Noise App — Which brown noise app to install, whether it is really free, and the five things an installed app does that a browser tab is not allowed to.
• Brown Noise Machine — Two very different products are sold as a brown noise machine, and one of them cannot make brown noise. What to check before buying.
• Brown vs White Noise — The widest gap on the site — 5.98 dB per octave, about 38 dB apart by 8 kHz — and what each colour can and cannot cover as a result.
• White Noise — The flat reference colour, measured at 0.00 dB per octave — the best of the five at making speech unintelligible.
• Pink Noise — Equal energy in every octave, measured at −3.07 dB per octave — the natural-sounding default and the audio industry's calibration signal.
• Brown Noise Generator — A real brown noise generator in the browser: built live at a measured -5.98 dB per octave, with no file and no loop point.