How to specify sound masking

Sound Masking Specification

One sound doesn't fit all - a more flexible approach

Introduction

The aim of sound masking is to elevate background sound levels to cover speech frequencies in order to reduce the intelligibility of mid to to far distanced conversations. In order to do this we use a sound which is deliberately similar to air conditioning as it is unobtrusive and should be unnoticeable to those who enter the space. All too often, however, specification is too prescriptive and compromises the final result.

Which Spectrum?

Which​ acoustic spectrum​ to use is the source of great debate but generally speaking there is a simple compromise at play. This compromise is between the pleasantness/unobtrusiveness of the sound versus its effectiveness. If a spectrum is created to simply mask speech frequencies in the most effective way it will be a ‘hissy’ often irritating sound unlike the air conditioning it is attempting to immitate. The compromise is therefore to find a spectrum which sounds pleasant but is effective too.

Here is one we made earlier. Smooth and effective - please feel free to steal!

Why not just use air conditioning?

Some feel that this is possible or even preferable and in older fan assisted air conditioned buildings don’t tend to specifiy sound masking systems, however, unfortunately, even though the existing airconditioning system might hit the desired overall dBA level (roughly 35-40 in rooms and 40-45 in open-plan), fan assisted aircon will almost always major on low frequency rumble and miss speech frequencies often entirely. Furthermore, traditional fan assisted air conditioning systems are never uniform in their coverage. In a room or across open-plan ducted aircon will be too loud in some areas and almost silent in others.

Specification

In order to get the best out of sound masking system, standard text book specifications are outdated. Although they will create a level playing field for manufacturers to compete they will usually push manufacturers to compromise their systems rather than embrace the now complex technologies available. Also, all too often, specifications overstep the mark and attempt to design systems by prescribing amplifier, speaker type or location when all that is required is a simple performance specification of a spectrum delivered uniformly and zoned to the local standards for cellular and open-plan space.

A more flexible approach.

The key to the success of the system is however more involved and this comes down the reality that every building and every type of fit-out is different and one spectrum does not fit all. More reverberant de-constructed interiors with vast expanses of polished concrete and glass will not sound like a more traditional fit out with suspended mineral fibre tile ceiling and carpet. We spend a lot of time tuning our systems to spectra that sound horrible only to be asked to come back in post occupancy to change it!

The final calibration should do more than simply meet specification. There should be a meeting of interested parties post calibration to discuss or tweak the spectrum to sound right in that particular fit-out. Once a system has been tuned for uniformity throughout the office space it is easy to change the spectrum to something that sounds better . Speech privacy can be can be tested live as can room to room privacy.

The final result is something that not only sounds great but will do the job its supposed to do without anyone noticing!