Acoustics Plus can provide the independent verification you need to demonstrate that your public address or voice alarm system is compliant with regulations.

Public address and voice alarm systems are one of our specialisms.  We have 15 years experience that helps to give the confidence you need in your design. Particularly critical when it comes to voice alarm systems. We work frequently with fire alarm and voice alarm contractors and are able to:

  • Provide evidence for you through computer modelling
  • Verify your design for you
  • Design a public address or voice alarm system for you
  • Test your system following installation

Can’t meet regulations because of factors outside your control?

We can support your case by providing you with evidence of what standard is achievable under the current circumstances. Where this standard does not meet regulations, we will advise on what measures should be taken to meet minimum standard.

Our voice alarm system experience gives you the confidence you need to meet the minimum requirements set out in BS 5839 and BS EN 60849. We work with sound system contractors and fire alarm contractors.


The audibility and intelligibility requirements of a voice alarm system can be stringent, so it’s critical that your voice alarm system is designed and specified properly.

We examine your specification requirements closely including checking target sound pressure levels and STI levels or whether post installation speech intelligibility testing (STI testing) will be required.

In addition we undertake a detailed evaluation of the space in which the voice alarm system will serve. This is often the determining factor in compliance with any performance specification and/or relevant standards.

Buildings still at design stage

We can carry out extensive acoustic room modelling using proprietary software packages to ensure that your voice alarm system design will meet your specification requirements.

If your voice alarm system cannot meet requirements because of architectural or acoustic constraints, we will provide you with scientific evidence.

Pre-installed systems

Our services include commissioning exercises to determine the electro-acoustic performance of your existing voice alarm system. This usually entails speech intelligibility measurement (STI testing) and audibility testing (SPL testing). We use the very latest measuring equipment to ensure the testing is undertaken in accordance with all the relevant standards.

It is critical for architects and specifiers of buildings to get the reverberation time of a space correct. We can measure and predict reverberation time.

Approved Document E of the Building Regulations and Building Bulletin 93 (BB93) for schools require the calculation of reverberation time to ensure stringent limits are met.

Consequence of incorrect reverberation time

If the reverberation time of a space is too long, communication of speech in more confined spaces such as board rooms can be difficult.

The opposite is true of larger spaces such as concert halls where a long reverberation time enhances the music performance.

Measurement of reverberation time

The measurement of the reverberation time of a space can be done using a loudspeaker or an impulsive sound such as that produced by a pistol shot. The measurement can be used to:

  • Calculate reverberation time in the common internal parts of buildings containing flats or residential rooms
  • Calculate airborne insulation of building elements (ISO 140 3/4)
  • Determine optimal speech intelligibility of spaces

Prediction of reverberation time

We are able to predict reverberation time using proprietary acoustics modelling packages or through detailed calculation depending on which is more appropriate.

The reverberation time of a space is determined by its volume and the surface finishes within the space. Hard, reflective surfaces such as glass, marble and concrete lead to long reverberation times and can create unpleasant acoustic environments.