Sodexo Justice Services have fitted out new offices for the Probation Service in many locations throughout the UK.  The new offices also serve as interview and drop-in centres for the service users, named Local Management Centres (LMCs).

The service users attend the LMCs and meet in acoustically treated booths within the reception areas.  To further improve the comfort and privacy in the area, B.L.Acoustics were presented with the requirement to supply and install sound masking equipment within a number of these offices to prevent other service users over hearing private conversations and interviews occurring in the booths.

Each of the offices were wide ranging in terms of size and shape meaning that to keep a consistent solution across each of the sites the system needed to be flexible enough to be cost effective for both small and medium to large installations.

Equipment Choice

The Cambridge Sound Management QtPro series sound masking system proved to be a suitable solution. QtPro systems provide precise control over where the masking sound is emitted. This means that sound masking is dispersed only in the spaces in which it is needed, eliminating unwanted spill over into adjacent spaces.

The system provides a uniform blanket of sound coverage throughout the space and is unaffected by ceiling design. The sound is transmitted as four uncorrelated channels, creating a more pleasant and comfortable masking sound to reduce noise distractions and protect speech privacy.

System Performance

There were three key elements that formed the acoustic performance requirement of the sound masking system.  These were strict parameters for sound pressure level, masking curve and the linearity of output across the area.

It was important to avoid ‘hot spots’ and zones of phase coherence between the signals emitted by the speakers across the fit out.  The system was commissioned and set up in such a way that the received noise levels at the measurement locations follows the curve established in within the specification, respecting the values stated in the form of one-third octave bands, from 100 Hz to 6.3 KHz, and with the acceptable stated deviations.

The specification also required that the system turns off at times of the day when the area is un-occupied.  The QtPro controller provides this facility as standard which allows the noise to ramp up and down at pre-programmed out-of-hours time periods.

One of the key factors to consider when installing a sound masking system is to ensure that it is not a disturbance to the users.  This is particularly tricky when the area is already in use and the occupants are already used to a particular environment.  One method of overcoming this is to introduce the noise slowly over a long period of time.  Once commissioned each system was muted and set to a ‘commissioning mode’ which slowly increases the level of noise each day over a period of a couple of weeks.

Each of the 17 systems were installed in-line with an ambitious installation programme.  Their performance has also been well received by the client.

“I wanted to pass on my sincere gratitude for a really well run project you’ve undertaken for Sodexo and the 17 CRCs. During installation works, your direct communications and liaison with the CRCs saved immeasurable amounts of my own and my colleagues time reducing the burden of relentless emails. Finally, your production of commissioning documents to comprehensively wrap up and close the project was swift and appreciated”

Damian Conway 
on behalf of Rider Levett Bucknall