40 Hz Test Tone – Play It or Download a 60-Second WAV

How it works

This 40 Hz test tone is a pure sine wave. Use it to check that a subwoofer reaches 40 Hz and to find what buzzes when it does. Tick each row of the rattle checklist as you check it. Save WAV downloads a 60-second file.

Read the full guide

Play it, or download the WAV

Press Play and the tone fades in quietly. On a subwoofer or full-range speakers, raise the Volume slider slowly until you can just hear or feel it. If the slider reaches half and you hear nothing, stop: the speaker may not reach 40 Hz. For a car stereo or TV, press Save WAV and copy the file to a USB stick or phone. Set the player to repeat one track. The file loops without a click, so any gap at the repeat is the player.

Walk the rattle checklist

Do the car checks parked, with the engine off. Begin with Door pockets and door panels, or in a room with Picture frames. Press a hand on the suspect: if the buzz stops, you have found it. Ticks stay in this browser, and the Share these settings link carries them. Clear ticks wipes them, and Undo brings them back for six seconds. Print the checklist gives a paper list for the car.

A rattle answers to its own frequency. If nothing buzzes at 40 Hz, try the chips from 20 to 100 Hz, or type the frequency a sweep found.
Change seats, not just head position. In a room over about 4.3 metres long, 40 Hz bounces between two walls and adds up: loud at the walls, quiet between them.
If a panel only buzzes when loud, keep each try to a few seconds. A box with a port stops cushioning the cone at very low notes, so keep 20 and 30 Hz quiet.

Questions and answers

What does 40 Hz sound like?

A low hum that you feel almost as much as you hear, just under E1, the 41.2 Hz lowest string of a bass guitar. Any grit or buzz on top is a fault nearby.

Is the 40 Hz test tone download exactly 40 Hz?

Yes. Your browser calculates a sine wave at 40 cycles a second and saves an uncompressed 16-bit WAV of about 5.8 MB. The volume slider's level is written into the file, so set the loudness on the stereo.

Does a 40 Hz tone do anything for the brain or health?

This page makes no such claim. It is a test signal for loudspeakers, rooms and cars, not a treatment, a therapy or a hearing test. The ear is far less sensitive below about 100 Hz, so a low tone that seems moderate may be loud.

All 27 rattle checks

In a parked car 10

Boot lid (trunk lid) or tailgate trim panel Push on the plastic trim with your palm. A clip that has let go buzzes against the metal: refit it, or put felt tape behind the panel.
Door pockets and door panels Empty the pockets first, because coins and pens are the usual cause. Then press along the edge of the door panel to find a clip that has come away.
Glove box and centre console contents Sunglasses, keys and loose change. Empty both before you blame the speaker.
High-level (third) brake light housing Press lightly on the housing at the top of the rear window. If the buzz changes, a thin strip of foam between the housing and the glass cures it.
Parcel shelf or rear deck Lift a removable shelf out and play the tone again. If the noise has gone, line the points it rests on with felt or foam strip. On a fixed rear deck, press on the trim and the speaker grilles instead.

Show all 27 rattle checks (22 more)

In a parked car, continued

Rear number plate (license plate) With the car parked, press a hand flat on the plate while the tone plays. If the buzz stops, put foam tape behind the plate or fit the two lower screws.
Spare wheel, jack and wheel brace (lug wrench) Loose tools in the wheel well ring against the floor. Tighten the wheel clamp and wrap the jack and brace in a cloth.
Subwoofer box loose on the boot (trunk) floor A box that is not fixed down shuffles and knocks. Strap it to the tie-down points or stand it on a rubber mat.
Sun visors and rear-view mirror Hold each one in turn. A visor that buzzes against its clip often only needs pushing fully home.
Unused seat belt buckles A buckle resting on hard plastic ticks in time with the tone. Clip it in or tuck it into the seat.

In a room 9

Cabinet and wardrobe doors A door that does not latch firmly will knock. Stick a small rubber bumper where the door meets the frame.
Ceiling light fittings and glass shades Switch the light off, let it cool and stand on a stable step. Look for a shade sitting loosely on its ring. Tighten the retaining screws by hand only, and never hard against glass.
Floorboards under the subwoofer Stand on the boards beside the subwoofer while the tone plays. If the sound tightens up, move the subwoofer or stand it on a paving slab or isolation feet.
Glasses, ornaments and remote controls on shelves Anything hard that stands on something hard. Move items apart so they do not touch, or stand them on a cloth.
Picture frames Touch the frame while the tone plays. Small felt pads on the two bottom corners stop it tapping the wall.
Radiator covers and heating grilles Press on the panel. Thin sheet metal buzzes easily: tighten its screws or put a felt pad where it meets the wall.
Suspended ceiling tiles and air vents Press a tile upwards lightly. If that stops the buzz, reseat the tile in its grid. A vent cover usually needs one screw tightened.
Television stand and wall bracket Hold the edge of the screen gently. Check the bracket bolts and any cable lying against the back panel.
Window panes and metal blinds A loose pane rattles in its frame and metal slats tick against each other. Raise the blind fully to rule it out.

The speaker or subwoofer itself 8

Amplifier running out of power A harsh, fuzzy edge that appears only above a certain volume is the amplifier clipping, not a rattle. Back the volume off until the tone is clean again.
Cabinet feet and spikes Rock the cabinet gently. If it moves, one foot is not touching the floor: level the feet so that all of them carry weight.
Cable or plug touching the cabinet A speaker cable or connector resting on the back panel buzzes against it. Move it clear or tape it down.
Driver hitting its end stop A hard clack on every cycle. Stop at once and lower the volume or the bass boost, because the cone has run out of travel.
Grille or dust cover Take the grille off and play the tone again. If the noise has gone, add a dot of felt where the grille touches the cabinet.
Loose driver screws With the tone off, check each screw round the cone with the correct bit, a quarter turn at most. Do not overtighten screws that go into chipboard.
No sound from a phone, laptop or small speaker Small drivers cannot move enough air at 40 Hz, so silence is the honest result. Do not turn the volume up to look for the tone.
Port noise A breathy flutter from the port tube and not a buzz. Air is moving too fast: turn the level down and check that nothing is blocking the port.

How this list was compiled: Checklist written for this page: the places a steady low tone most often shakes loose in a car, in a room and in the loudspeaker itself, each with a way to confirm it by hand and a fix that needs no special tools. Car parts carry the British name first and the North American name beside it. The figures in the page copy were checked on 2026-09-18 and again on 2026-09-19: the speed of sound in air at 20 °C, about 343 m/s, at https://en.wikipedia.org/wiki/Speed_of_sound; the note E1 at 41.2 Hz at https://en.wikipedia.org/wiki/Piano_key_frequencies, and E1 as the lowest string of a four-string bass guitar at https://en.wikipedia.org/wiki/Bass_guitar; standing waves between the walls of a room, with a sound pressure antinode always at the walls and a loudness that differs from place to place, at https://en.wikipedia.org/wiki/Room_modes; the ear's lower sensitivity below about 100 Hz than between 2 and 5 kHz at https://en.wikipedia.org/wiki/Equal-loudness_contour; and, checked on 2026-09-19 at https://en.wikipedia.org/wiki/Bass_reflex (section Limitations), that below the tuning frequency of a ported enclosure the port unloads the cone, which can then be driven past its safe mechanical limits, and that an undersized port makes wind noise or chuffing. Computed, not looked up: 343 divided by twice 40 gives the 4.3 m that a room dimension needs before 40 Hz can stand between two walls; 60 seconds at 40 Hz gives the 2,400 cycles of the saved file; and 2,880,000 samples at two bytes each give its 5.8 MB. How the file is made (whole cycles, 16-bit mono WAV at 48,000 samples a second, the volume written into the file) was read from this site's own tone generator code on 2026-09-19. Licence: own work

40 Hz Test Tone for Subwoofers and Rattle Hunting

Rattle checks for a 40 Hz tone