Part 2
TROUBLE SHOOTING CHURCH ACOUSTICS,
THE PRO'S AND CON'S.

Since most churches have a problem or would wish to avoid a problem, here are some after the fact solutions.

Pillars.

In old cathedrals of Europe and in a few churches in North America, pillars were used to tune the church. Slots or holes in the back of a pillar were cut to select the offending frequencies. By adding sand, or as done recently in Chicoutimi, Quebec, adding blown insulation, you can tune the pillars. If a mistake is made, the sand can be removed from a hole at the base of the pillar. The pillars greatest effect is on the sound quality of the Pipe Organ and congregational singing. Pillars tuning is still being done today and it is possible to retrofit an existing church with pillars.

Ash Pots.

Ash pots were first used by the Greeks, then the Romans and later in Northern Europe. The technique is very simple and effective. Where ever there was a known or planned acoustical problem, clay pots of various sizes would be built into the walls of the church or theatre. The most common walls were the back walls and rear corners. After many trial and error tests, an employee of the church would fill or empty the pots with ash for various function. Today this same technique could be used. You can replace the ash with fiberglass insulation which is reusable. Us a silicone spray on the fiberglass and it will reduce the dust and keep the fibers from falling apart. A better alternative would be an adjustable Helmholtz Resonator. Please read the book Architectural Acoustics, David M Egan, published by McGraw Hill, 1988 or "The Masters Handbook of Acoustics" Second Edition F. Alton Evert, Tab Books 1989 for further details.

Slotted Blocks.

Slotted blocks have been around for a long time. Slotted blocks were often combined with the clay pot system. Today, the slotted block is a very attractive system that stands on it's own. The principal is simple. Take a standard 8 x 8 x 16 inch block. Cut a slot from top to bottom of the block to a certain width for the frequency you want to control. Add some fiberglass inside of the block. When finished, you can paint or wax the block or cover with curtain or cloth. The block companies that manufacture these blocks also make different size chambers within the block and the have different surface finishes that don't need to be painted. These blocks work well for mid and low frequency control and they are generally interior blocks.

Cinder Block.

Depending on who the manufacturer is, this system has many names. The most common appearance of the system is 12" x 18" x 3" flat panel. Usually the back of each unit has a mounting deck that raises the units about an inch from the wall. These units are effective for mid and high frequency control. Although the manufacturer claims are accurate, they are very misleading. If you have a room with an internal volume 50,000 cubic feet, the literature will say that all you need is 1 or 1.5% of material to treat the room or 750 units. What they are not saying is that 3 of the walls have to be cover from floor to ceiling to get the desired results. Using these products requires more than a siding scale to figure out.

Split Face Blocks.

A split faced block is nothing more than a block with an exposed shape. There are many patterns and styles. Usually the exposed shape is 2 inches deep or less. These blocks are also often called Architectural blocks and they are treated a decorative block. The Acoustical properties of these blocks are very limited. Some times you will see a 6 or 8 foot ring of these blocks in the upper half of a school gyms. Although an Architect will state that he chose those blocks for their acoustical properties and smile for his wise choice, an acoustical expert will notice right away that two of the walls should have had the spit face block from the floor to the ceiling and an eight foot ring in the other two walls. The spilt face block is not very efficient in distributing or absorb sounds. The split faced blocks combined with other systems can be very attractive.

ASC Tube Traps

A functional Bass trap, high frequency diffuser and mid range absorber makes this product the most effective. Although they cost a few dollars more, you need far fewer of them when compared to other sound control objects. ASC tube traps were designed originally as a recording studio product. When this product was unleashed to the church community, it has literally performed miracles as some minister would express its. The beauty of the product is three fold. First is being able to trap a lot of bass sounds in room corners in a small package. Almost all churches have corners including domed churches. Bass always builds up in the corners. ASC Tube Traps traps the bass without reducing the high frequency range noticeably. Secondly it absorbing mid range sound. By spacing the traps at difference widths, you can change the amount of mid range absorption. The third effect is diffusion. The diffusion occurs from 500 hertz and up. Usually you don't want to absorb high frequency in a church. The Tube Trap can maintain the singing quality of a church while fixing the low frequency problem areas. As a side benefit, in every installation of ASC Tube Trap that I have visited, the organist always make comments like, "there is more bass coming out of the organ" or "the music is easier to follow and play. I didn't realize how much poor acoustics were restricting our ability to perform" (Scott Tyler, St. Paul's United Church, Bowmanville, Ontario, Can.) ASC products can be used on their own or be used with other products.

RPG Diffusors. (Reflection Phase Grating)

Diffusion is often used to solve acoustical problems. For years, the acoustical community was looking for a diffusive surface that gave a uniform diffusion of sound energy. Such a system was invented by Manfred R. Schroeder, a professor at the University of Gottingen, Germany and at AT & T bell Laboratories at Murry Hill, New Jersey. The panels have many different sizes and shapes to accommodate almost any acoustical condition. The panels have long wells which are cut to different 1/4 wave lengths deep. The well depths have a very specific pattern. Each panel is based on the "Maximum Length Sequence Code". Today the general term is Diffraction Grating and many acoustical engineers design their Diffraction Grating Panels.

The RPG diffusors is trademark of a ready made, of the shelf, effective system of, non-patented panels which are primarily made of wood. The Following is a Quote from the book, The Master Handbook of Acoustics, Second Edition, by F Alton Everest (TAB Books)

"In churches, there is always conflict between the intelligibility of the spoken work and conditions for full enjoyment of the music. The rear wall is often the source of reflections which create disturbing echoes. To make this wall absorbent is often detrimental to music conditions. Making the rear wall diffusive, however, minimizes the echo problem while at the same time conserving precious music and speech energy. Music directors or often faced with the problem of singers or instrument players not hearing each other well.... Surrounding the music group with an array of reflection phase grating diffusors both conserves music energy and spreads it around to achieve ensemble between musicians."

The combination of RPG products and ASC Tube Traps offers the most versatile and complete solution to any church with acoustical problems.

Noise Busters. Pressure Zone Phase Diffusers. Noise Busters - (A Customized Acoustical Product)

Tectum (Spaghetti Board)

Tectum is one of those products that you love to hate. When used properly, Tectum tiles an panels work great. However, because they are so cheap to buy and every Architect has a "Guide Book" from the manufacturer, Tectum usually gets installed in a broad and indiscriminate way. As a result, Tectum gets installed in such a way that it solves one problem very well, but it creates other problems. In a Gym or a Cafeteria, the latitude in using Tectum is quite broad, but in a church, there is a fine line between how much you use, how it is installed and which surfaces it is installed on.

Tectum is an inert fiber board that comes in thickness from 1 to 4 inches. When exposed, the panels look like compressed spaghetti. Although it is paintable, the Guilford Cloth covered products are better in a church. When painted, the Tectum will shift in frequency.

Sonex

Sonex is a patented foam system. In comes in square panels from 1 to 4 inches thick. These panels are very efficient high frequency absorbers. Their best use is for attenuating high frequency in a church. A very effective application of Sonex is under balconies and around entrance areas where you don't want sound from the foyer disturbing people in the sanctuary. If you have a high frequency problem and you need to cut down about 3 seconds at 4000 hertz, you will not need very many traps to do the repair.

Carpets and Curtains

Once upon a time, a church used a little bit of carpet to solve a problem. Today, most church have a problem because of carpets and or curtains. Carpets in the church are often installed without any consideration of the consequences. What most "Experts" and builders often do is lump carpet and Padded pews together. A church that has padded pews is just trying to keep the same Reverberation Time (RT60) for when the church is full or empty. Carpet is a surface treatment. It has short fibers that absorb high frequency sounds very well but! reflect low frequency sound energy back into the room. There is a big difference between padded pews with carpet and without.

The rules for carpet are as follows.

1. When the internal volume of the room greater than 20 times the floor space, you can use carpet in the isles.

2. When the internal volume of the room greater than 30 times the floor space, you can use carpet in the isles and pew areas.

3. For every square foot of carpet installed, you have to install a 150 to 500 hertz mid range bass absorber that has equal or greater efficiency in absorption.

Electronic Reverberation Systems

The newest and most exciting system of solving a whole array of acoustical problems is the Electronic Reverb Systems. There are several systems available and some custom systems as well. It is a system that consists of microphones, speakers, amplifiers, electronic digital reverberation and a complex matrix system. When adjusted properly, these system can often make up for poor acoustics and also shape the reverb time to be natural. However, it can not correct acoustical problems such as bass build up or standing waves, but, you can often hide echoes and in some cases improve intelligibility.

The plan is to make the house of worship sound like a recording studio. Make the room quiet, free of obvious acoustical problems and use the reverb system to restore the desired acoustics as needed.

In Europe, there is a successful system called the ACS or Acoustical Control System from Holland. Although North American installations of such systems are limited, these systems offer the widest solution a church can ask for. From personal experience in installing and using an ACS system, it gives the best performance for everyone to experience. In the United Church installation which sat 600 people, the Organist or Soundman were able to switch the acoustical performance to match the event during the service.

There were four preset position. Position one was for Organ, acoustical instrumental and Singing solo performances. The reverb time in this position was at it's longest. Position two was for choir performances. In this position, the reverb time was slightly shorter and the microphones nearest the choir were turned up higher to assist the choir. This helped the Organist to balance to the choir. The third and perhaps the most important setting was setting three. In this position, the reverb system was adjusted of optimum congregational singing. The audience mics were turned up while the mics near the organ and choir where turned down. Setting four was for speaking, although a proper sound reinforcement system was used as well, the reverb system was adjusted with a short reverb time above the balcony while under the balcony, the speakers were turn up with a little more delay time. As a result, a separate delayed system under the balcony was not needed. One neat effect was when moving from the main part of the sanctuary to under the balcony, - you didn't notice the roof over you head until you looked up.

An Electronic Reverberation Systems can have many more presets and are a great partial or complete problem solver, and, they do represent the latest in modern technology for meeting today's needs of a multi purpose sanctuary.

Summary

In church acoustics, these are just some of the most common techniques seen. The cost of a good acoustical system that solves most of your real major problems can vary. Please note the words "solve most of your problems". This is due to the fact that some building shapes are so poor, that rebuilding the church would be cheaper that trying to solve a problem until it is reasonable. However, there are some compromises you can live with. Accepting minor compromises will keep acoustic solution costs down. From experience, the average one time cost of an acoustical solution works out to be from $30 to $55 per seating position in the house of worship. Therefore a church that seats 400 people including choir loft seating should spend no less that $12,000 for a meaningful solution than will satisfy most church members and no higher than $22,000 for extreme cases. If you get a second opinion that is over $55 per seat, it is time to consider condemning you church sanctuary and build a new house of worship. These same figures are of 2 or 3 times higher than the cost for planning and doing the acoustics in a new church building. If your church is considering an electronic solution, be prepared to make a one time investment between $70 to $130 per seat plus correcting any existing major acoustical problems.

OK, now that you have just received some of the best knowledge on church acoustics available, now you can get the technical books on acoustics design your church acoustics right! Wrong!!! Just because the church down the street did it or you read of a solution in a book, it does not mean that their solution is right for your church. You might have a one of a kind problem (which happens not too often). Although many consider me as a doctor (an expert), the truth is, I have all of my work check out by other experts before a recommendation is made. There are just to many variables that can be easily over looked. One wrong number in a calculation can cost a church thousands of dollars. I have never yet met a church that had an unlimited budget like some government projects seem to have. Churches can't afford experiments. Churches need solutions.

Church acoustics is 40% science, 10% art, 40% skill from experience and 10% inspiration. Judging from the many churches that I have visited over the past 15 years, all you see is 100% perspiration, 100% desperation, no art, no skill and no science. Isn't it time for the church communities to define their needs and use science, art and skill to set acoustical standard? Lets stop using a Band-Aid approach to church audio and acoustics. If you want to see perspiration, be a surgeon - half way through open heart surgery, be told that there are no more sutures or stitches left in the hospital. All you have to work with are Band-Aids. What do you think the patient will say when he wakes up? - Sorry, I was not implying that churches are asleep!

Some statements and Specs have been blanked out under the understanding that it is part of the "intellectual Knowledge" guidelines and were not part of the original article. Such knowledge has value and can be purchased through investing in the book "

"Why Are Church Sound Systems and Church Acoustics So Confusing?"Info on a book on Church Sound System & Church Acoustics

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Copyright (c) 1996 JdB Sound, Acoustic Lab.

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