By Jean-Pierre Dalbéra from Paris, France [CC BY 2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons

As I described in the previous post in this series, soundscapes have numerous components, which are the sounds from individual noise sources (cars, people, trains, a dishwasher – whatever). When your brain processes the sound, some of these components will stand out in your conscious awareness, while the rest are not processed consciously, but form part of the unconscious “backdrop” of your experience. This mental background affects mood, task performance and other things, even though you are not consciously aware of its presence.

The sounds that DO reach your conscious awareness affect you in a very different way – they may convey information (speech), they may transmit aesthetic values (music), or they may cause annoyance (an aircraft overhead).

How your brain decides which components of the soundscape will become conscious and which will not is something that neuroscientists have yet to unravel completely. However, from experience acousticians have developed a few rules of thumb. Sound that does NOT become conscious – that is, sound that forms part of the mental “background”, is generally:

• fairly constant over time;
• broadband – that is, it sounds more like a “shhhh” or a rumble than a “la” on a particular note;
• relatively low in sound level (loudness); and
• lacking information content – for example, there are no intelligible words.

Typical examples of sounds that become part of the mental background are distant traffic noise and noise from an air-conditioner.

The first job in designing a soundscape is to design the background sounds – what are they, and how loud are they? This should also be the first job in modelling a soundscape in SoundSoup. Ignoring background sound results in spaces (and models) that sound “empty” and unreal. It also means that other sounds will be more audible and potentially more annoying than they should be.

What should the background sound be? One source is mechanical systems within a building, typically noise from the air-conditioning system. In SoundSoup this would be modelled by an interior sound – “Air-con vent noise”, under “Mechanical”; “Air-conditioning”. Other mechanical sounds can be reasonably simulated by the “Fridge” sound, under “Miscellaneous”, “Interior Sounds”.

In some cases you may also want to use “piped” music as a background sound. There are two options for this in SoundSoup under “Music”, but beware, they need to be used in addition to other background sounds or they will become conscious.

Another common background sound is traffic noise, generally heard through a window, wall and/or door. This is an external sound, and in SoundSoup, among sounds that can be “outside a wall” there are a number of samples for “Traffic”. The loudness of the traffic noise inside the room depends, of course, on what type of wall, window and/or door construction you use.

So how loud should the background sound be? You can find help in an Australian Standard – AS/NZS 2107:2000 “Acoustics—Recommended design sound levels and reverberation times for building interiors”. This sets out a range of recommended BACKGROUND sound levels, in decibels (dBA) for many types of space. They represent typical background sound levels in those spaces – outside that range, either above or below, and the space will sound odd.

I can’t post a copy of that Standard here because it’s copyright, but you can buy a copy here, and many libraries have copies.

So, in either designing or modelling a soundscape, the first step is to decide on the dBA level of background sound that you should have, using AS/NZS 2107, and decide on what sources will produce that sound and how they will produce it.

Remember:
• We’re talking about BACKGROUND sounds here – fairly constant, fairly quiet sounds that you will not be conscious of. These do not include sounds from people, buses or anything else that varies in time or has information content;
• The target dBA level from AS/NZS 2107 applies to the TOTAL of all the BACKGROUND sound sources. You can calculate this total in SoundSoup-Pro.

Once you have an appropriate level of background sound in your space, the next step in soundscape design is to control intruding sources. That is the subject of the next post.

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