*CAPS™ Standard

Church Acoustical Performance Sound Standard
a work in progress

A Church acoustical standard. (OK Performance Standard) The standard meets the following criteria;
  1. With a slightly raise un-amplified male voice speaking at an average sound level, that voice should be heard clearly and understood at 70 feet in front of the person talking with listeners who do not need hearing assist hearing aids or or have less that 20% hearing loss in both ears. (give or take 20 degree off center) (Intelligibility of 90% or better using STI and RASTI measurements with a 5" point source test speaker and microphone)
  2. The audience should be able to understand most of the words the choir is singing.
  3. The room needs to be good for congregational singing
  4. The Congregation should be able to hear themselves when they sing.
  5. The Choir should be able to hear themselves when they sing.Soloists or musicians should be able to hear themselves fill the room with their sound and judge how loud they need to perform with or without amplification
  6. The room has to allow a mono or stereo point source sound system to have an intelligibility score of 92% or better in 90% of the seating or up to 100 feet of the main speaker system.
  7. The noise floor of the room should be below 45dB flat. (this is so the sound system doesn't amplify the noise in high gain situations.
  8. The sound system should not be used to make the air conditioner louder.
  9. The room should be free of echo's
  10. The room should be free of flutter echo's
  11. The reflections in the room should not be so loud that it encourages people to lower their voices.
  12. To assist in the performance of a sound system to the extent that it can amplify a child's voice when the mic is 3 ft away and broadcasts the sound up to 75dB to the back of the room.
This standard is Based on the best performances of 800 churches tested. From the 800 churches, this is what we learned.
  • Church Sizes were from 180 to 8000 seating
  • 42 acoustical parameters were used for testing each church (Parameters from MLSSA Testing.)
  • 16 parameters were common to 8 of the 800 churches - which were deemed the best performing houses of worship that met the above standard
  • 47 churches met 6 of the standards
  • 88 churches met 5 of the above standards
  • The rest of the churches only met 3 of the standards or less. Any room that can only pass less than 4 of the standards is deemed unsatisfactory for worship - regardless of denomination or worship type.
The 8 best sounding and performing churches had these common acoustical parameters:
1. RT60 Average
2. RT60 at 150 Hertz
3. RT60 at 250 Hertz
4. RT60 at 500 Hertz
5. RT60 at 1250 Hertz
6. RT60 at 2000 Hertz
7. RT60 at 4000 Hertz
8. RT60 at 6000 Hertz
9. Signal to Noise Ratio
10. Intelligibility
11. C50
12. NC
13. NC Flat
14. Room Volume Ratio
15. Room Shape
16. Overall frequency response of the room
The 88 churches had these 6 basic statistics.
1. RT60 Average
2. RT60 at 250 Hertz
3. RT60 at 2000 Hertz
4. Signal to Noise Ratio
5. Intelligibility
6. Overall frequency response of the room
The following list is a summary of worship styles based on the 6 basic elements that can be easily measured or planned for in new construction or when changing the acoustical performance of a house of worship. (The list is based on a worship space that has a signal to noise ratio of 25dB 50 ms after the first arrival and a **room intelligibility score of 90% of better.) (%alcons is used to maintain continuity of the data that has been collected since 1987) Meeting these standards does indicate a house of worship with a satisfactory level of performance.
Worship Style Type RT60 at 250 Hertz RT60 at 2000 Hertz
Protestant Traditional ***1.50 1.50
Protestant Contemporary 1.40 1.40
Catholic Traditional High Mass/Latin 1.85 1.85
Catholic Traditional 1.67 1.67
Catholic Contemporary 1.51 1.51
Baptist Traditional 1.58 1.58
Baptist Evangelical 1.41 1.41
Anglican/Episcopal Traditional 1.65 1.65
Pentecostal 1.31 1.31
Vineyard 1.29 1.29
Presbyterian Contemporary 1.45 1.45
Greek Orthodox 1.72 1.72
Synagogues 1.60 1.60
** Room Intelligibility score is when no sound reinforcement sound system is being used for testing. It is a test of just the intelligibility of the room and nothing else.
*** A error of 2/10th of a second can put the worship space into another class of room or make the room unsatisfactory.
Statically, churches that have these acoustical qualities are also churches that have better attendance, strongly supported by the communities, have higher facility usage or more frequent community events, better supported financially, higher property value and tend to spend less money on their sound systems.

Statically, churches that meet the CAPS™ Standard cost the same or less that other churches of equal size that do not meet the CAPS™ Standard. The suggestion here is that having good acoustics is not a cost issue but a education issue with Architects, Church Boards and Building Committees, and other acoustical professionals who do not specialize in church projects.

What does all of this mean? Regardless of the standard, there are certain requirements or rules that all church sanctuaries must have regardless of denomination or style of worship. These are items that are not optional in the design of a church.

The first rule is a background noise level of 45dB flat. That means the air conditioner, the ceiling fan, the sanctuary lighting, the heating system, transportation noise, toilets and heating systems can not make a noise louder than 45dB flat. That also includes noise for sound system amplifier cooling fans, video projectors and noises and hums from the sound system as well.

The reason for this requirement is that to hear and understand speech, you have to be 25dB above the noise. When a church fails in this requirement, it has to do one of two things. You have to increase the sound level of the spoken word, but in doing that, people complain that the speech is too loud. When you turn down the sound levels to where they are comfortable, you will have trouble understanding speech. Either way, a minister's ministry is being compromised every week.

The second rule is the signal to noise ratio of the room of reflected energy in the speech range. Speech has most of it's energy in the 90 to 1200 hertz range. This is where the fundamental sounds are. The harmonics of speech sounds makes each voice unique. These are the high frequencies. The range of them is 1000 to 5000 hertz. The signal to noise in this case is the amount of direct sound vs. reflected sounds. When the reflected sound arrives to the listener is louder than -25dB after the first 50 milliseconds, it degrades speech. For long term or intense listening, this is an important standard. Long term listening is a sermon over 30 minutes. For 20 minute sermons you can tolerate -20dB of noise from wall reflections.

Now there is a segment of the audio and acoustical community that says you can hear well with only -15dB of signal to noise. This is generally the standard used for many live theatres. Such a standard is OK for people who only have to listen to a show once or twice a year. In a church where people are doing the same type of listening over 50 times a years, you can't afford to fatigue people with difficult listening conditions. It takes more effort to understand speech with excessive room reflections or room noise. The better the signal to noise and the quieter a room is, the more people stay awake, alert and able to understand the sermon rather than just trying the hear.

* CAPS™ Standard is a register trademark of JDB Sound Acoustics Inc.

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