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Background sound cannot block voices, but it can blur them so they stop resolving into words. Sounds with energy between about 1 and 4 kHz, such as pink or white noise, do this best; deep sounds such as brown noise do much less.
Why speech is distracting
It is hard not to follow words you can understand. Much of what makes speech understandable sits in the consonants, roughly between 1 and 4 kHz. Blur that range and voices become sound rather than sentences.
Which sounds cover it
A sound with steady energy in that range does the most at a given volume. Relative to each sound's own overall level, at 2 kHz White static measures −7.8 dB, Velvet noise −8.6 dB and Deep brown −14.5 dB. Brighter noise has more where speech lives; deep sounds such as brown noise and cabin sounds have much less.
Band by band, in numbers
| Band | Deep brown | White static | Difference |
|---|---|---|---|
| 2 kHz | −14.5 dB | −7.8 dB | +6.7 dB |
| 2.5 kHz | −15.7 dB | −7.2 dB | +8.5 dB |
| 3 kHz | −16.7 dB | −6.6 dB | +10.1 dB |
| 4 kHz | −18.1 dB | −5.7 dB | +12.4 dB |
| 5 kHz | −19.2 dB | −4.8 dB | +14.4 dB |
| 6 kHz | −20.0 dB | −4.2 dB | +15.8 dB |
| 8 kHz | −21.2 dB | −3.5 dB | +17.7 dB |
| 10 kHz | −22.4 dB | −3.8 dB | +18.6 dB |
| 12 kHz | −23.5 dB | −4.6 dB | +18.9 dB |
Louder is not the answer
Raise the sound only until nearby speech stops resolving into words, and no further. Closed headphones help most, because they reduce the voices before the sound has to cover them.
