Room Acoustics

PLEASE NOTE: All this information and more will soon be available at www.soundapart.co.uk

(This site is currently under construction, but will soon become the dedicate site for all things related to our room acoustic services and solutions).

Our room acoustic services break down into two key parts as follows:

  1. Onsite acoustic surveys; whereby we come to site and perform an acoustic survey within each room or space where issues with poor sound quality are being experienced, (more details on this below).

  2. Provision and onsite installation of recommended remedial measures designed to help absorb excess levels of reverberation.

 

The onsite room acoustic survey includes the following:

  • RT60 reverberation tests to measure the current levels of reverb, in particular across the frequency spectrum from 125Hz to 4000Hz, (this covers the full range of frequencies at which human voice is spoken)

  • Background noise level tests

  • General survey to assess the construction and architectural characteristics of the room.

  • Assessment of the nature and probable causes of the sound behaviour currently being experienced within the room

  • Consider what type of remedial measures might be appropriate whilst assessing how and where they could be applied in keeping with the end clients own specific aesthetic design parameters.

The whole onsite element of the survey will takes approx. 45mins per room. Thereafter a report will be created based on the findings and test results, along with recommendations for remedial treatment.


 

Room acoustic assessment criteria

If a meeting or conference room is to be used for collaborative meetings involving video & audio-conferencing technology, it is imperative that the room acoustic issues are taken into consideration in order to combat any adverse effects they may have on the speech intelligibility experienced, both within the room itself and at remote sites to where video and audio calls will be transmitted to.

This acoustic quality of a room can be affected by two key issues as follows:

  1. Reverberation time, measured in seconds, (also referred to at RT60)

  2. Background noise levels measured in decibels (dB)

Studies have shown that poor speech intelligibility can cause participants concentration levels to drop off, thus having a direct impact on productivity.

There are standards to refer to when recommending appropriate levels of reverberation time and background noise levels in meeting rooms and spaces designed for speech-based activity, according to their size and volume.

References to these standards as shown below.

BS8233:2014 ‘Sound insulation and noise reduction for buildings’ states acceptable reverberation times for unoccupied rooms used for speech. This is shown in Table 4.1 below.

Room Volume m3

Reverberation Time T seconds

50

0.4s

100

0.5s

200

0.6s

The following table shows the values of the recommended background noise level in accordance with DIN EN 11690:

Type of room

Recommended back ground noise level (dB)

Conference room

30 – 35 dB (A)

Office room

30 – 40 dB (A)

Open plan office

35 - 45 dB (A)

These standards are supported and often referred to within accepted literature and recommendations issued by manufacturers or audio and video conferencing technology, as a basis of “best practise guidelines” for preparing a space for video and voice enabled conferencing.

What is Reverberation Time (RT60)?

Firstly, sound reverberation is created when a sound/noise reflects off a hard surface i.e like an echo effect. Multiple sound reflections can occur, if many large sound reflective surfaces, such as glass, painted plasterboard, concrete, hardwood and veneered wood etc, are present in a room. This means that without the presence of an appropriate amount of sound absorbent material in the room, the energy driving the sound around the room takes longer to fade away.

Reverberation Time (RT60), is basically a measurement of how long it takes the energy of a sound burst to dissipate by 60 decibels from its initial energy output or until it is completely inaudible.

If the reverberation time builds up beyond what is recommended, according to the room size, then it can start having a negative impact on the intelligibility of speech and in particular speech/voice signal that is to be picked up by conferencing microphones.

For example, if the reflected sound from one syllable is still heard when the next syllable is spoken, it can make it difficult to understand what was said, words such as "Cat", "Cab", and "Cap" may all sound the same.

Reverberation time is frequently stated as a single time value, (as in the standards table above). This single value quoted is generally derived from an average of RT60 time values taken across a range of frequencies at intervals known as “octave bands”, from 125Hz to 4000Hz. This range of frequencies basically represent the full spectrum of human speech as it exits from our mouths.

The six key octave bands measured breakdown as follows: 125Hz, 250Hz, 500Hz, 1000Hz, 2000Hz and 4000Hz.

If a room is to be acoustically treated to combat excess levels of reverberation, then it is imperative that the reverberation time is measured and tested correctly, producing a breakdown of the reverberation times across all six frequency octave bands.

It is important to understand this breakdown of reverberation times because it will help determine what type or class of acoustic treatment is the most appropriate to apply in order to combat the problem effectively.

Factors that affect a room's reverberation time include the size, shape and construction materials used, along with all the items the room is furnished with, including chairs, tables, large display screens, whiteboards etc.

Why do we measure Background Noise Level?

Sources of background noise can be anything from air conditioning units and building services to activities from adjacent office space and street/traffic noise seeping in from outside.

Basic theory suggests that a sound signal i.e your voice for example, should project approx. 25 dB higher than consistently occurring background noise in order to be understood clearly. The average sound level for normal spoke voice is approx. 65 dB (if measured at approx. 2m), therefore it stands to reason that the higher the levels of background noise, the louder you may need to speak to be heard properly.

If you then combine a need to speak louder with excess reverberation levels in the same room, then speech intelligibility will begin to deteriorate rapidly.