Make a joyful noise to the Lord, all the earth! [Psalm 100:1]
By Rev. Paul Wooley
One of the most important considerations, when either planning or attempting to improve a church sound system, is to consider the acoustics of churches or parish halls.
When a sound system is underperforming, there is a tendency to attempt to solve these situations by spending money on electronics, microphones, and speakers. However, this often doesn’t help.
Often, I have dealt with people that have made a statement such as, “I don’t need a microphone or system, because I can project my voice loudly”. However, loudness doesn’t solve basic acoustics problems, it can even make things worse.
I tell people that they are always ‘fighting with’ the acoustics of the room. A basic understanding of room acoustics can help you avoid many pitfalls.
Imagine two people standing two meters apart and who are on a 20-metre-high platform in the middle of a 50-hectare farm field on a windless day. When one of these people is speaking to the other we can say that something like 99 44/100% of the sound is travelling from the mouth of the first person directly to the second person. In acoustics, this is referred to as Direct Sound. The situation that places these people away from any sound-reflecting surfaces is termed ‘Free Field Acoustics’.
Now imagine placing these people still two meters apart in a small room, with highly reflective walls, floors, and ceilings. The listener is now receiving a mixture of direct sound and sound that is being reflected from many surfaces with each path causing a delay in time. Our ears and brain will struggle to sort out the received sound mix in attempting to understand the speaker.
Hopefully, you can now see that the size of a room, the reflecting surfaces, and the placement of the sound source and the hearer/receiver of the sound is critical to our understanding of a room’s acoustics.
One of the most fundamental concepts in solving acoustic problems is the Ratio of Direct to Reflected Sound!
From this follows some important primary measurements of any space, which describe both the nature and amount of reflected sound:
EARLY REFLECTIONS - these are sounds that arrive at your ear less than 1/10 second after the direct sound which are caused by surfaces very near the source and give ‘life’ to the sound. Without them, things sound ‘dead’.
REVERBERATION is complex reflected sound energy which is perceived as separate from the direct sound. This is due to continued reflections in the room after the original sound has stopped. It has these three basic characteristics:
Strength – the loudness of the reverberant sound in comparison to the original direct sound.
Decay – the time that it takes for the reverberation to die away after the direct sound stops. This is given as RT60, which is how long it takes to decay by a factor of a million (60db). A ‘dead’ room, such as a movie theatre, will be less than one second. A concert hall for symphonies might be around two seconds, whereas a very large cathedral will be more than ten seconds.
Frequency balance – some frequencies in the reverberation may be louder than others. The persistence of low frequencies gives a “warmer” sound while more high frequencies will sound “brighter.”
ECHO is a long-distance reflection of the sound source, which is perceived as a separate sound source. A surface would have to be at least 17 meters from a sound source to create a perceivable echo.
The purpose of this series of articles, and particularly this beginning article on acoustics is to give you at least some basic understanding so that you might at least be able to evaluate suggested solutions to acoustical problems.
Often there are simple and inexpensive solutions, such as adjusting how speakers are aimed to avoid highly reflective surfaces and to focus the sound on the congregation. Additionally, microphones often need to be adjusted to avoid picking up reflected sounds and preferentially picking up only the speaker.
Questions: If you have questions about church sound systems, email Paul+ at email@example.com. We will try to answer them in future issues.
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Rev. Paul Woolley is a retired priest in Huron. He has 55 years of experience working with audio equipment of every description for varied venues.