Why Most White Noise Machines Don’t Block Low-Frequency Noise

You have been running your white noise machine at maximum volume to drown out the stomping from above, the neighbor’s bass-heavy music, or the rumbling of the trucks passing by.

Or perhaps you tried to cover an obnoxious hum permeating your room.

Alas, the white noise machine didn’t help all that much.

Now you are wondering what is going wrong.

Perhaps your machine was even set a lot louder than the noise you were trying to block.

Why does your white noise machine not mask low-frequency noise

To use white noise (masking noise) to drown out (mask) intermittent disturbing noises (noise intruders), the masking noise needs to have two characteristics:

It needs to be louder than the noise intruder.
It needs to contain the frequencies of the noise intruder, or at least be relatively close.

With low-frequency noise, the problem most often is point number two:

The speaker of most white noise machines cannot reproduce the low frequencies that are disturbing in low-frequency noise intruders (e.g., bass-heavy music, footfalls, rumbling), or at least it cannot produce them loud enough.

As a result you’ll hear loud white noise and you’ll hear the neighbor’s footfalls or subwoofer.

“A duet so to speak.”

Note: Additionally, because the speaker cannot reproduce low frequencies well, many manufacturers filter (roll-off) the low-frequencies from their white noise to prevent distortions.

Take a look at the dominant frequencies in a footfall caused by someone walking on a wooden floor, recorded in the downstairs apartment

The footfall’s max sound level is at around 40 Hz, but there is substantial energy between 20 and 70 Hz.

Now let’s look at the lowest-pitched white noise (dark-brown noise) of one of the largest white noise machines on the market:

Note how the area (below 100 Hz) where most of the footfall’s sound energy lies is mostly white.

The white noise sound level at around 125 Hz is about the same as the footfall’s maximum sound level, but unfortunately it is at a much higher frequency.

Note: Because of our hearing is more sensitive at 125 Hz than at 40 Hz, the white noise machine will even appear louder than the stomping noise. But it is louder at higher frequencies only!

At 90 Hz, the white noise machine’s sound level is already 10 decibels lower.

At 40 Hz—the frequency of the max footfall sound level—the white noise machine’s output is more than 20 decibels lower.

Roughly speaking, -10 decibels is being perceived as half as loud.

So -20 decibels at 40 Hz, means at 40 Hz, the white noise is only 25% as loud as the footsteps.

That is merely a drop in the bucket when it comes to masking this stomping noise.

We would have to raise the sound level of the machine by more than 20 decibels to have any hope of drowning out the footfalls, but the machine is already running at 90% volume.

But even if we could increase the volume to completely cover the footstep noise the result wouldn’t be good:

The white noise would have become so loud at other frequencies that it would be disturbing and likely detrimental to our hearing.

To drive this point home, here is the low-frequency spectrum of a popular Hip Hop song

(Frequencies above 300 Hz are filtered to allow for better focus on the problematic frequencies.)

Again, we have a peak at around 40 Hz and substantial energy between 20 and 80 Hz.

Now, whether the bass is as mean as it looks depends largely on what speakers are used to play the song.

A small Bluetooth speaker can’t reproduce the low frequencies either, so it can be matched with a good white noise machine.

But, if the neighbor uses a quality subwoofer you can expect a very accurate reproduction of this song with all bass-frequencies coming through, and commercial white noise machines don’t stand a chance.

Which white noise machines can mask low-frequency noise?

None of the commercially available white noise machine I know of can mask louder low-frequency noise. None of them has a speaker that can reproduce the low frequencies with enough energy.

But, white noise can certainly be used to mask low-frequency noise: You just need a much larger speaker and connect it to a white noise source. Good subwoofers can go as low as 30 Hz (and some even 20 Hz).

A subwoofer-powered white noise machine can mask low-frequency noise

If you already have a white noise machine with a headphone jack, try connecting it to your subwoofer, and play the lowest-pitched white noise.

If you don’t have a machine, I recommend you use a white noise app like myNoise for this purpose.

With myNoise you can fine-tune your white noise to emphasize the low frequencies while not blasting out loud sound at the mid-and-high frequencies (where you don’t need it).

I call this low-frequency-emphasizing sound dark-brown noise.

You can shape the white noise so that its frequency spectrum looks pretty much like the disturbing noise (see charts above) you want to get rid of.

For detailed information on how to do this, read my post “How to Block Loud Footstep Noise.”

There is a limit to this though: If the noise intruder is too loud, you would have to play your subwoofer at a sound level that would disrupt your sleep all by itself.

Also, you can’t completely mask noise or vibrations that you feel (e.g., in your chest).

Headphones also go much lower than the speakers of standard white noise machines

If you don’t have a subwoofer or other large speaker, you can also play your dark-brown noise via good headphones.

Preferably use active noise cancelling (ANC) headphones, but good standard headphones can also reproduce the low frequencies.

ANC headphones offer more relief because they reduce (cancel) low-frequency noise better than any other tool I know of.

If the low-frequency noise that disturbs you isn’t too loud, you won’t even have to use a masking noise.

But even if your ANC headphones don’t quite manage to completely cancel your noise intruder, they can reduce it substantially so you don’t need to play your masking noise nearly as loud as you would have to with normal headphones.

For more information on using headphones to block low-frequency noise please read my post “How to Block Bass Noise—and Save Your Sanity.”

Conclusion

Good commercial white noise machines tend to work well against mid-and-high frequency noise (e.g., speech, barking, creaking, honking, crickets, etc.).

But, because they have relatively small speakers, they don’t reproduce low frequencies well.

These frequencies, however, are needed to mask low frequency noise intruders (e.g., footfalls, the bass of EDM music, rumbling, compressors etc.)

To mask low frequency noise, make your own white noise machine: try playing low-frequency emphasized white noise using a subwoofer or good headphones.

To learn more about masking/blocking low-frequency noise, read the following articles:

I wish you all the best.