White noise. Sound conditioning. Many words are bandied about when attempting to describe sound masking. But what is it, actually?

Sound masking is a sound introduced into a space to increase the background sound level for the purposes of reducing either or both the impact of intrusive noise and the intelligibility of speech.

This can include natural sounds like water flowing or bird song, digital sounds like white or pink noise, or specialised masking sounds. It can even be as simple as a radio.

Technical definition

For those scientists among you, the technical definition comes from Australian/New Zealand Standard AS/NZS 2007:2016 (section 5.3) as follows:

In spaces where acoustic isolation and speech privacy are important and the sound levels are below the lower level of the recommended design range, there is an increased risk of inadequate acoustic masking. Where this occurs, the loss of acoustic and speech privacy can be a significant concern. In these situations acoustic masking can be introduced into the space to raise the sound level to within the recommended design sound range level in Table 1. 

Doesn’t exactly tell us what sound masking is, but it’s as good as we get for an official definition. But what’s more important is the actual sound.

What does it sound like?

It depends on what kind of masking sound you use. Commercial sound masking systems use blended randomised sounds. A lot of people liken it sound to airflow. Kind of like the sound of being on an airplane—although not nearly as loud! It can also be mistaken for air conditioning—although it should be randomised so it doesn’t become repetitive like the mechanical aircon unit.

In contrast, white noise is more like a detuned radio, which is a harsher, hissing sound at a higher frequency. This kind of sound hasn’t been used in commercial sound masking systems for decades.

Natural sounds like waterfalls and ocean waves are sometimes used as sound masking, but they are technically not sound masking but “soundscapes”. Often soundscapes have a commercial masking noise blended into the natural sound to make them more effective. Whether you’d want a burbling brook in your office permanently, though is a matter of personal taste.

Is there a best masking sound?

My personal preference is a sound that has more “bottom end”, which I find more comfortable. However, this is a personal preference. Others might prefer a slightly different blend. Sound is subjective because our auditory perceptions vary depending on age, hearing loss, and so on.

This is why an unobtrusive masking sound that will blend into the background is actually the best sound. Sound masking should be part of the furniture, not a noticeable feature.

The best way to optimise sound masking is to ask an expert.