Evaluation Guide

Part 1. Church Sanctuary Acoustics

We would like you to try these tests as best you can and report back in via e-mail with your results. Let us know if you can think of other tests as well. We are always looking at ways to make the HIS System standard universal. Your contribution would be much appreciated.


The following tests will help you understand the performance of the sanctuary and the interaction relative to the acoustics of your church or hall. These tests are only meant to show potential weakness which should be followed up with a detailed test to find solutions. Most of these tests can be done with a SPL meter such as the ones sold by Radio Shack or with free software downloaded from the internet. Mark your score in the box. At the end of this article, each test is explained. (You may want to print this file direct to your printer. It's about 12 pages long.)

Name of Church ____________________________

Age of Existing sound System ______ yrs.
Age of the Existing Church ________yrs.

Part 1. Church Sanctuary Acoustics

* These tests should be done with a computer

  1. (1.) What is the NC (Noise Control level) of your church? (Best done with a computer*)
    1. NC 20 = 10
    2. NC 25 = 10
    3. NC 30 = 9
    4. NC 35 = 8
    5. NC 40 = 2
    6. NC 45 = 1
    7. NC 50 or higher. = 0
  1. (2.) Reverberation Time average (required reverb meter or Computer*)
    1. 0 to .8 of a second = 4
    2. .9 to 1.3 seconds =7
    3. 1.31 to 1.9 seconds =10
    4. 1.91 to 2.4 seconds =6
    5. 2.41 to 2.8 seconds =2
    6. 2.9 seconds or longer =1
  1. (3.) Reverberation Time at 200 Hertz (required reverb meter or Computer*)
    1. If Longer than average = 1
    2. If shorter than average = 10
    3. If by more than half of the average time =0
  1. (4.) Reverberation Time at 3000 hertz (required reverb meter or Computer*)
    1. If Longer than average = 10
    2. If shorter than average = 1
    3. If by more than half of the average time =0
  1. (5.) Echo Test 1 Do this test with a friend - Stand at the center pulpit or center to the chancel area and clap your hands once.
    1. If you hear an echo or reflection of the clap = 1
    2. If no echo is heard =10
  1. (6.) Echo Test 2 Do this test with a friend - Stand at the center of the sanctuary seating area and clap your hands once.
    1. If you hear an echo or reflection of the clap = 1
    2. If no echo is heard =10
  1. (7.) Articulation score of the Sanctuary - Must be done with a computer* or with the Bell Telephone speech oral test.
    1. 0 to -74%=1
    2. -75 to -82% =7
    3. -83 to -89%=8
    4. -90 to 100%=10

* Computer Systems accepted are TEF - MLSSA - Bruel & Kajr - Ariel - Smaart

Each test is a window into the world of church sound. To the non church community, the acceptance of poor sound is common. For the church community, poor sound week after week is insulting, degrading and costly. Today, there are many churches that have better sound than any local establishment within a 20 mile radius. These are affordable systems that are well designed systems. For this reason, there is no excuse for any church to not have a good sound system It's not just a Spiritual reason for good sound, it also makes economic stewartship. The following tests will let you know the strengths and weakness of a church sound system and its acoustics.

The following in a partial explanation of each test.

Question 1. - What is the NC of your church?
The "NC" of a church is one of the most important scores. The NC or Noise Control level of the church describes the background noise in the sanctuary. Background noise has profound implications. Here is one of the main problems with high levels of noise.

Typical conversation levels are between 55 and 65dB (decibels). We often use 60dB as an average. To hear speech at a comfortable level and to be able to understand the words being spoken, the level of speech usually has to be 25dB above the noise. Since the quiet side of speech is about 55dB, a room with a noise floor less that NC30 is an excellent listening space. The most common places that have such low NC ratings are bedrooms and living rooms that are away from kitchen noises.

This is why many people turn off their TV sets or music during a conversation. This is why it is so hard to hear on a telephone in a street phone booth that has a lot of traffic. This is also why people leave the kitchen when appliances are hard at work. In a church, especially larger churches, an NC above NC35 is a serious problem.

The other thing that you must be aware is that NC is not a constant throughout the Sanctuary. The hum of the florescent lights or ceiling fan above the platform or alter can raise the NC in the front of the church to NC40 while the rest of the church is NC30. When a poor sound system is in place, ministers have to swallow the mic just to be heard and the NC doesn't matter since sound quality of poor to begin with. When a high performance sound system design is being used, the system will be able to amplify the noise from the lights. That means the minister has to always be close to the microphone. This also means the Lapel mics will be limited in performance and not work very well.

In other words, a new sound system will be restricted in it's performance before you even get started when the NC level is above NC35. As question 7, part 2 implies, if the sound system design is right, then having a working distance of 18 inches to 3 feet is normal in rooms with NC35 or lower. This make the system forgiving. It allows the minister to take a step back from the mic without his voice disappearing from people in the back rows. It means lay people, children and all events will be heard.

Finally, there is one combination item about the NC score that is constantly overlooked and not tested. Echo's and late reflections. Read below, echo test 1 for details.

To test the NC of a church, you can use a SPL meter that can measure down to 20dB. With such a meter, you can take to following readings.
- - - - - -125 Hz - - - 250 Hz - - 500Hz - - 1000Hz - - 2000Hz - - 4000Hz
NC-40 = 56dB - - - - 50dB - - - 45dB - - - 41dB - - - - 39dB - - - 38dB
_____NC-35 = 52dB - - - - 45dB - - - 40dB - - - 36dB - - - - 34dB - - - 33dB
NC-30 = 48dB - - - - 41dB - - - 35dB - - - 31dB - - - - 29dB - - - 28dB
 
Question 2. -Reverberation Time average
The average reverb time(1) in a church is one of the first clues as to whether there are problems or not. The age old hand clap provides a wealth of knowledge to the trained acoustical expert. However, you don't have to be a expert to recognize the obvious and doing something about.
In my book, "Why Are Church Sound Systems and Church Acoustics So Confusing?", it has carefully broken down the reverberation requirements into three type of church services. Traditional(2), Evangelical(3) and Charismatic(4).

The Traditional or Liturgical style of worship can make good use of longer reverberation times. However, any reverb time that is longer that 2.5 second is not need and it is no longer musical unless it is well diffused. When churches have more that a million cubic feet of air space, the rules of reverb time are different and are covered in detail the book. If the reverb time in your church is longer than 2.5 second, then you most likely have a problem with both music and speech. Yes, this also degrades the performance of a church organ too. A shorter reverb time is ideal.

The evangelical church has a middle of the road requirement that is the hardest to achieve. Generally, they put a higher emphasis on speech and amplified music while at the same time, they want their churches to have a traditional sound for choral and congregational singing. As a result, such churches require a prolonged reverb time that does not interfere too much with speech or amplified music. Almost a neutral space. Generally, a reverb time of 1.5 seconds is about perfect. A large(5) church can have it as high as 1.7 while smaller churches(6) should be around 1.4 seconds.

The Charismatic church or the Pentecostal church is your electronic church. People don't like to hear such terms thinking that it takes something away from Christianity. On the contrary, since their preaching is of a fundamentalist type, they preach that all things come from God. It is who or how an item is used that matters. The other element that they have in their worship is drama and theater. With such a broad list of requirements, a reverb time less that 1.35 seconds is idea.

Reverberation Time at 200 Hertz
Not all reverberation is equal. Long reverb times in the low/mid range of speech is not good. From experience, the ideal reverb time at 200 Hertz is when it is within 2/10ths of a second of the measured average time. For your style of worship. Longer reverb times below 500 Hertz will have a profound affect on speech degeneration.

Also, longer RT60's below 500 hertz will also limit the ability to hear bass sounds when you are near a wall or near the source of the bass sounds. Although getting the bass player at least 15 feet away from his bass speaker is idea, a room that stores excess bass energy is also creating the same effect. Remember, the wave length of 200 hertz is 5.6 feet and 100 hertz is 11.25 feet. If the bass player is standing closer to the speaker than the length of the sound wave, in order to hear it, he has to wait for the sound to bounce of a wall that is further than the wave length and perpendicular to the source. This often means that the sound has traveled to the other side of the room and come back. Also, if the bass player is back up against a wall, he/she still will have problems hearing the bass sound. If your bass player is playing to loud, don't blame him. Look at the room and check out the bass response. If you have excess energy below 500 hertz, fix that and you will have better control of your bass sounds.

 
Reverberation Time at 3000 hertz
High frequencies of sound gives a sound it character. It is the high frequencies that gives a sound it's wholeness. It is also high frequency that give music the expressions we love and enjoy. Although younger people get carried away with bass and rhythm sounds, without high frequency sounds combined, the sound is meaningless. The tick of the drum stick striking the skin on the drum, the crash of the cymbals before the ring it makes, the twang of the electric bass guitar are all distinct because of the combined high and low frequency sounds. It also the high frequency sounds that gives us our intelligibility clues.
Without high frequency sounds in speech, no one would be able to understand each other. This is more so for the English and German languages. Other languages that are Latin based such as Italian, French, Spanish and Portuguese, rely on a strong mid range of sound for distinction. Many European language churches do well with shorter high frequency reverberation times. For English speaking churches, a reverb time at 3000 hertz that is up to 3/10ths longer than at 1000 hertz or the "average" does well. However, in a highly amplified service(7), a reverb time at 3000 hertz or 3k, is better when it is equal to the average RT60.
Echo Test 1
Do this test with a friend - Stand at the center pulpit or center to the chancel area and clap your hands once.
An echo heard at the pulpit or center of altar/platform area affects the performers, minister and sound system. It is bad enough for a person to sing and hear an echo return when they are two words further along in their music. When a sound system is being used as well, the echo will be louder. For years people have be trying all kinds of sound system tricks to minimize the problem. But lets face the facts, it's still a Band-Aid solution. This is a problem for everyone. Just because you have carefully aimed the speaker system to minimize an echo problem, a person singing in an operatic style who does use a sound system will have problems. Also, if you listen carefully, if the Organ and Piano is at the front of the church as well, they too have a problem will keeping time to the music. Moving the Piano and Organ usually costs more than fixing the problem. If you hear a echo, fix it.
The best form of fixing an echo is with diffusion if the reverb time is OK. If the reverb time is long, you can combine the acoustical repair to correct for RT60 and echo. If the reverb time is long in the bass range, that also can be corrected with the echo problem.
Echo Test 2 Do this test with a friend - Stand at the center of the sanctuary seating area and clap your hands once.
If your church congregation likes to sing, then echo's in the seating area need to be fixed. Of course, the issue of fixing the problem is much like the age old "chicken and egg" question. Do we fix the room even though the congregation already sings well? Do we fix the room to get the congregation to sing better? Do we even have to discuss it? If a pipe leaks water, do you fix it?
The best form of fixing an echo is with diffusion if the reverb time is OK. If the reverb time is long, you can combine the acoustical repair to correct for RT60 and echo. If the reverb time is long in the bass range, that also can be corrected with the echo problem.
Articulation score of the Sanctuary
Articulation is the understand of words spoken. A speech Intelligibility test is when 20 or more volunteers sit in the pews in a scattered pattern while a person they are not familiar with reads from a list of words on a score sheet from the pulpit or main speaking position. The listener will hear 50 words at 10 second intervals. Each person will have a matching list. The list has 50 rows of words and there are 6 words per row. They are to mark down the words they thought they heard. The first 20 rows are word with common suffixes, the next 20 rows are words with common prefixes, the last 10 rows are word that sound alike.
Regardless of the size of church, this test is to be done without a PA system and people sitting in the first 8 rows of seating. If your church is very wide at the front or if your church is spread out in a fan type seating pattern, then get some rope and have everyone sit within 90 degrees of the speaking area or 45 degree from center. The person speaking can raise their voice, but not so much as to be straining. This will make it harder for the listener.

If the reverb time is longer than your style of worship requires, then the score will be lower. If the NC of the room is high, the score will be lower. If the RT60 and NC is good, if there are no echo problems, then the score should be high. Any score below -88% is unacceptable.

Endnotes

  1. The average Reverb time or RT60, (RT60 is the time it takes a sound to decay 60 decibels. Often a starters pistol is used to measure RT60) is often calculated at 1000 Hertz. Modern computer systems can give you a average time over the speech range, music range or whole hearing range. Speech range average RT60 work the best for music in a church.
  2. The Traditional style of service refers to churches that have only acoustical presentation of music. This includes choral and recital presentation. This also means that music is always presented at a moderate to low levels, rarely above 80dB. For these churches, music takes up less that a fifth of the worship service or less that 4 songs of worship.
  3. The Evangelical style of service will have an active music program that includes both amplified and acoustical presentations of music. This is when music from "tape accompaniment", electronic instruments and vocal support for congregational singing. These are the churches that will have up to a 1/3rd of their worship time in music, song and praise.
  4. The Charismatic style of worship or Pentecostal type services are churches that will have half of their service in music, song, praise and special music events almost every service. Almost everything is amplified. These churches will often present their music at or close to Rock and Roll Concert levels.
  5. Larger churches seat over 1200 people.
  6. Smaller churches seat 300 people or less.
  7. A church that amplifies 90% of all of their music - specials, choral and Piano/Organ accompaniment to congregational singing.



 

Part 2. Sound System Performance

Part 3. Sound Equipment Specs


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Copyright (c) 1996 JdB Sound, Acoustic Lab.
Last updated, January 11, 1996
April 2008