There is no doubt that some houses of worship and historic buildings can be challenging spaces for live PA systems. Whether you require an audio system for a one-off event or a permanently installed system the issues you face will be similar. In this article, we will look at what causes the problems and we will explore the ways to combat them.
What’s the problem?
Hard floors, hard walls, high vaulted ceilings, void spaces and square angles are all common architectural features of old churches and this means that sound bounces around rather than being absorbed, it is reflected again and again until it gradually decays below our hearing threshold. This causes a type of echo known as reverberation (reverb for short). The reverberation time in old churches or historic buildings can be several seconds so is very noticeable. Reverberation is an acoustic property of the space. It isn’t anything to do with the sound system so there is nothing that can be done electronically to improve this – you cannot twiddle a knob and turn down the rooms acoustic reverberation!
Is it echo or reverb?
Reverb is not the same as an echo. In an echo, you would hear the sound repeated distinctly. For example, if you shouted ‘hello’ you would hear the word ‘hello’ repeated, each time getting quieter and quieter. This is usually because the space is very big and it has hard surfaces constructed parallel with each other. This allows the sound to bounce back and forth rather than bouncing around and getting scattered.
Where echoes exist playing live music becomes practically impossible as the musician will constantly hear themselves playing but with a delay added and repeated. Anyone who has made a telephone call where they can hear themselves talking with a delay will know that it is very challenging to continue.
In contrast, a reverberant space will have smaller dimensions or surfaces at different angles allowing the sound to bounce around in a more random fashion.
Using PA systems in reverberant spaces
It can be challenging using a sound reinforcement PA system in a very lively, reverberant space. Before installing a permanent sound system or rigging a temporary one for a special event it is important to consider the following points.
Microphones for reverberant spaces
As a general rule, it is important to use microphones with a directional pickup pattern. Typically cardioid or hypercardioid microphones will provide a better result as they can be directed towards the sound source and will pick up less of the ambient sound. They will also provide a better gain before feedback occurs as, when correctly positioned, they will pick up less of the amplified sound from the loudspeakers.
Directional microphones need a bit more care in both placement and their use. As their pickup pattern is more controlled it is increasingly important that the speaker or instrument is in the optimum position.
It is common for people to want to use a tie-clip radio microphone as they are convenient and discreet for presenters who want to move around. Due to the nature of how they are attached to clothing, the pickup pattern of most tie-clip mics is omnidirectional – they pick up sound from all directions. Cardioid mic capsules can be used with radio mics but care has to be taken to position the microphone accurately on the clothing. Often a better option is to use a head-worn microphone. These will provide better sound levels as the distance between the mouth and microphone is reduced so the gain is increased. In addition, the microphone moves with the person’s head so the level remains constant.
Loudspeakers for reverberant spaces
The basic principle of speaker choice and placement is that you want to direct sound to where it is needed (the listeners) and avoid sound going elsewhere where it can bounce around the building and cause nuisance reverberation. There is more than one way to achieve this and the best solution will depend on the nature of the building, practicalities and budget.
As with microphones, some loudspeakers are more directional than others. It is the higher frequency sounds that can be controlled and speakers with a horn are able to direct sound to radiate out over a specific area. Dispersion of 90-100 degrees horizontally and 50-60 degrees vertically are typical characteristics and this will allow at least some part of the frequency band to be directed at the audience and reduce the amount of reverberating around the space.
Line array loudspeakers will allow more precise control of the sound dispersion, particularly in the vertical plane as well as benefiting from the reduced sound level fall off from front to back (a significant feature of line array loudspeakers). This would allow more of the sound to be directed to the audience, where you want it, and less in areas where it will cause issues with clarity.
The two examples above work by controlling the direction of the sound from the loudspeakers. An alternative is to control the volume. If you have two speakers at the front radiating sound they need to be loud enough to provide a suitable volume at the further point from the speaker – usually the back of the church or auditorium. The volume at the front will be significantly louder than the back. It doesn’t need to be that loud at the front but if you turn it down it will be too quiet at the back. In this scenario, there is a significant amount of extra sound being produced and radiated into the space that will reverberate and reduce the clarity of the sound.
Instead of having just two speakers that need to be driven quite hard the alternative is to have many speakers positioned throughout the auditorium. Because the distance from the speaker to the audience is less, the speaker does not need to be as loud and less sound is radiated into areas where it will reverberate. This type of distributed speaker system lends itself well to churches with pillars as the speakers can be mounted at regular intervals close to the congregation.
The distributed speaker solution can be improved on further by using loudspeakers that have directional control of the sound by either a horn flare or line array element.
I’ve observed many PA systems in houses of worship and there are plenty of times that I have noticed distributed systems where the sound is coming out of all speakers even though there is only a small area of the church being used. It is not uncommon for the congregation to be relatively small and seated within a small section of the nave so in these situations it would be helpful to be able to turn down the volume in unused areas so the level of reverberated sound is reduced.
Tips for dealing with difficult acoustics
1. Deaden hard surfaces
Where possible use soft materials to deaden hard surfaces. In an old church building, you may not have many practical options for this but if using a sports hall or similar space for a temporary event it may be more possible. Carpet will make a big difference and is available as a relatively inexpensive single-use floor covering for events. Even if covering all the hard walls is not possible putting up heavy drapes, such as our serge pipe and drape, on the wall opposite the stage can help a lot.
2. Brief the presenters
Make sure that your presenters are briefed properly. There are many presenters who think that because they are using a microphone they don’t need to speak up. Ensure that all presenters/speakers are aware of the challenging acoustics, are briefed on good mic technique and speak loudly and clearly. We find that a quick chat with the presenters puts them at ease, gives them a little understanding and achieves a much better result.
Any live PA system has a maximum amount of gain that can be achieved before feedback. It is a multiplication effect, so a small reduction in the volume going into the system will make a big reduction on what can be output. Similarly if the presenter is able to raise their voice slightly it will result in much more output and ideally you want to be in a situation where you have headroom and not driving everything on the limit of feeding back. I would advise them to speak confidently as if they are talking to the person at the back of the room. If they do this they will provide a good level in a natural manner.
3. Keep it short
Keep ‘listening sessions’ short as active listening in reverberant spaces can be fatiguing for the audience. If necessary have frequent breaks or vary the type of activity to keep the audience attentive.
4. Read the lips
Facial expression and lip reading aids communication so if the audience is too far away to see this clearly the addition of a close-up live camera feed shown on big screens will help the audience follow what the speaker is saying.
5. Microphone choice
Choose microphone types carefully so that the pickup of unwanted sound is minimised and the gain before feedback is maximised. Typically this will involve directional, cardioid or hyper-cardioid microphones.
6. Loudspeaker or PA system choice
Put the sound only where you need it with controlled dispersion or distribute speakers carefully throughout the space. Amplified sound should be focussed on audience areas and minimise sound being projected into unoccupied areas.
7. Zone it
For permanently installed systems build in zone control so that speakers in unused areas of the building can be turned off.
8. Operate it
In an ideal world, it would be great to have a PA system that just works without the need to push faders or twiddle knobs. This scenario is achievable in many situations but when you are faced with challenging acoustic spaces it is often better to have a trained person or audio engineer operating the system. An engineer will be able to optimise the mic setup for the event, reduce the number of open microphones and make small adjustments to what’s happening in real time. The difference can be relatively small but it can also be the difference between hearing and not hearing.
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