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5.1 Acoustics

The acoustic design and performance of buildings is a technical issue for which a specialist may be required, but because it is an issue that has big implications for the practical use of your building it is very helpful if you at least have a feel for the subject.

There are two main acoustics issues for churches to consider – firstly the sound characteristics of the main spaces – certainly the worship space, but also entrance spaces need to be considered – and secondly sound separation between spaces within the building, and between the building and your neighbours.

Echo … Echo … Echo…

The acoustic feel of a space depends partly on its shape, but also on the materials on its surfaces. The smoother and harder a surface, the more the sound bounces off it without losing any of its intensity. This reflected sound either reinforces the sound you are hearing direct from the source, so making it clearer, or gets confused with the original, making it difficult to ‘hear’ (ie decode) what is being said or sung.

Unwanted Noise

Before we consider spaces for worship, let’s think about a welcome space or foyer. The feel of the space will be completely different if it has a low ceiling or a high one. If the foyer has a low ceiling with hard surfaces on both ceiling and floor (eg plaster above and floor tiles below), the acoustic will be a problem. If there are a number of conversations going on then the space can rapidly fill with noise as each conversation gets louder in order to compete with the others. The result is bedlam! Where the floor needs to be hard-wearing and smooth the reverberation in the space can be hugely reduced with absorbent surfaces on the ceiling (for example perforated plasterboard) and soft furniture.

Worship Band

For many of you reading this, music in church means an amplified band. In one sense this makes life easier, because by investing in a half-decent AV system you can tailor the amplification to suit the space. But it is still worth understanding ‘traditional’ acoustics, because you will also want the spoken word to sound as natural as possible.

‘Traditional Acoustics’

Sound is a form of energy that is transferred by movement of the air, in sound waves. In the open air, a voice or other sound can be heard clearly if you are close enough, and will stop as soon as the voice stops. By contrast, a sound inside a room will be reflected many times between the different surfaces of the space, with the reflections arriving later than the direct sound. Acousticians refer to the ‘reverberation time’ of a space which is measured in seconds.

Different surfaces will reflect different amounts of the sound energy that hit them – ranging from almost 100% for the smooth hard surfaces in a tiled shower, to almost nothing for an absorbent surface like the lining of a recording studio. Soft surfaces like carpet, cloth upholstery, curtains, hangings are all acoustically absorbent, as of course are people. The issue is to get the right combination to allow for the appropriate effect.

To project an unamplified voice into a large space you need hard reflective surfaces behind and on the floor (and, preferably, ceiling) immediately in front of the speaker, giving the voice more carrying power; drapes behind and carpet in front will ‘kill’ the sound. For speech to be audible in a large space you do not want too much reflection, which will give you a long reverberation time and too much echo; but nor do you want no reflection, because this will give the space too ‘dry’ an acoustic. Similarly, for congregational singing you need some sound reflection, because without it people cannot hear themselves, and become reluctant to sing – which is why the bath is a good place to sing (at least for the singer…).

Separation – Rock Concerts And Quiet Prayer

As we have said, sound is a form of airborne energy. There are therefore four principal means of creating separation between adjacent spaces. Let’s imagine two adjacent rooms separated by a wall; the options are as follows:

  • Ensure the two spaces are sealed from one another – any cracks or holes (typically made for routing cables and pipes) will let most of the sound through, making the rest of the construction irrelevant.
  • Make the partition heavy, because the heavier it is, the more energy is absorbed in the sound passing from the air of the first room, into the partition, and then into the air of the second room.
  • Make the two surfaces of the partition work independent of one another, for example with ‘resilient bars’ between the plasterboard or other lining and the frame structure of the wall; these act like shock absorbers.
  • If the wall has a framed structure the voids should be filled with an appropriate insulation to prevent them acting to amplify the sound, in the same way that the body of any stringed instrument does.

Movable Partitions

Movable walls that slide and fold away can be fantastic for making flexible use of a building. Many of these can provide impressive levels of acoustic separation, such that a loud voice in one space is not intelligible in the next. This is really very impressive, but it does come at a cost. You can spend £10-£20,000 or more – ie the cost of a nice new car – on a set of such doors, and that may be money very well spent if it gives you an appropriate benefit. But because they are trying to do a lot of things at once, these are often quite fragile pieces of equipment, and ideally should only be operated by someone who has been trained to do so; in most cases that is wholly unrealistic, in what is a community building open to all sorts of users.

So the advice is to think hard about whether you really need your partition to provide that level of acoustic separation. Victorian schools often used sliding folding partitions without any of the rubber seals or clever mechanics that are needed to create that sound separation; these don’t create as much sound separation, but are often still going strong 120 years later. We can promise you the same will not be true of the modern partitions you may wish to install…