Acoustics of Worship Spaces

April 21

2014AdityaGanvendra Singh ChaharRashmi RaySaurabh RohilaVibhor Gupta

Term Paper Report, Noise Engineering

IntroductionMost but not all worship spaces will be in one of three categories, characterized by reverberation times appropriate for different music styles. A congregation should first consider where it fits among these styles.

Contemporary Music : These spaces often seat a large congregation in a fan shape. They will have a reverberation time in the range of 1.0 to 1.5 seconds. A primary goal is to make the room friendly to the sound system. All speech and music are usually amplified with electronic instruments frequently used. The preachers often employ a wide dynamic range in their voices. This system is designed to provide powerful music. The sound of the music is controlled more by the audio system than the room. The room is designed to avoid harmful reflections, which often requires significant wall treatment. The room volume should be limited to prevent the need for excessive added absorption that could hurt congregational singing. The sound system is often expensive because of many sophisticated production features and powerful music capabilities.

Classical Music: These spaces place a strong emphasis on classical music and organ. A reverberation time in the range of 1.7 to 2.2 seconds requires careful design of the sound system for clear speech. Some rooms may have longer reverberation times, making it very difficult to achieve clear speech. The most successful of these rooms are usually arranged in the classical "shoe box" shape with a moderately high to high ceiling. Those congregations planning to invest in a pipe organ should consider this style. To preserve loudness of congregational singing, the room should be optimally sized to reduce the need for added absorption. This means the sound system must be carefully designed to aim the sound into the people and minimize wall reflections and reverberant sound. The system designer should be selected carefully. The sound system may be expensive because of the speakers needed to control the placement of sound for speech. Supplementary stereo music loudspeakers may be desirable.

Affecting factors• Reverberation time

• Speech clarity in room

• Strength of sound (dB level)

Room features• Wall material

• Ceiling design

• Flooring

• Room dimensions and their comparison with normal music rooms, concert halls.

• Seating arrangement

Worship Space Acoustical Design Tips1. Treat architectural acoustics as an important part of the overall design. Begin evaluating acoustics at the schematics and early design stages.

2. Acoustical engineering and consulting firms throughout North America have the expertise to make sure you "get it right acoustically." Whenever possible, bring a consultant on early in the design stage to work with your architect.

3. Audio/video professionals can be helpful with architectural acoustics, but, remember, their training is in A/V equipment design not architectural acoustics. Verify your consultant's experience in architectural acoustics, hopefully with similar projects.

4. Beware blaming the audio equipment for poor room acoustics and design. Conversely, installing a new audio system, when the problem is actually the room design, can be very disappointing.

5. There are often aesthetic and interior design adjustments required in order to achieve great acoustics. Maybe that beautiful domed ceiling that will focus sound into one small area is not such a good idea.

6. Acoustical interiors products, sound absorptive panels, acoustical diffuser panels, and overhead sound reflectors can greatly enhance the acoustic quality in a space. Proper selection and location of acoustical finish materials, along with a good room design, will optimize acoustic quality.

7. Too much reverberation reduces sound clarity and speech intelligibility.

8. Too little reverberation reduces the quality of music and creates an acoustically "dead" space.

9. Controlling unwanted sound reflections can be done with acoustical absorber panels, which reduce the sound intensity of the reflection, or sound diffusers, which scatter the sound.

10. Concave or inwardly curved wall or ceiling surfaces focus sound. This can be a negative if the focusing occurs at the listener level.

11. Convex or outwardly bowed surfaces scatter sound. Irregularly shaped surfaces scatter sound. This can improve acoustics in a large space by maintaining a desirable level of reverberation and sound intensity while more evenly distributing sound throughout the seating area.

12. A quiet space allows speech and music to be best heard and enjoyed. Design the HVAC system and the shell of the space to keep the background noise in the room very low.

Church Acoustics:The contemporary church is built around communication— verbal, musical, andemotional — as well as worship. The minister communicates with the congregation by preaching, leading prayers, and announcing church activities. Music attempts to communicate ideas and concepts while it simultaneously enhances the worship experience through emotional involvement.

The acoustics of the worship space have a profound impact on all of these functions.A space is said to have good acoustics if it provides the sound environment conducive to the way we want to use it. For a worship space to have good acoustics it must allow good verbal and musical communication. It has poor acoustics if it makes that communication difficult.

Roll of Reverberation:This reverberation can be a thing of great beauty, as the listener is able to hear many notes of a musical solo layered on top of each other, enriching the sound beyond measure. Reverberation can also be disastrous, as the listener is subjected to different parts of a word or sentence piled on top of each other at the same instant, making it difficult to understand speech. This is the basic conflict of acoustics which are great for music but bad for speech. A well designed sound system can overcome this kind of conflict.The optimum reverberation time for a space in which music is played depends on the type of music that is to be played in the space. Rooms used for speech typically need a shorter reverberation time so that speech can be understood more clearly. If the reflected sound from one syllable is still heard when the next syllable is spoken, it may be difficult to understand what was said. "Cat", "Cab", and "Cap" may all sound very similar. If on the other hand the reverberation time is too short, tonal balance and loudness may suffer. Some reverberation is very desirable to enhance singing by the choir and the congregation. It is hard to sing in a dead, non-reverberant church. A good reverberant environment is one which provides a pleasing mix of direct and reflected sound to enhance the musical

experience. This is accomplished by a careful combination of regular and irregular room geometries and surface finishes.

Design of ceiling of a church:A shallow vaulted ceiling is better than a flat ceiling. Most churches build their vaults running front to back so that there is a high wall section at the front. However, a shallow vaulted ceiling actually sounds better if the vault runs side to side. This is because the sound is stored in the high volume part of the space, which is located under the peak of the vault. So, the sound is stored side to side in the area where the people sit.

Furthermore, people's ears are separated sideways so we are more sensitive to side to side sounds. People tend to like the spacious effect of side to side sound storage. A slightly sloped ceiling at the front of the church moves sound away from the front towards the congregation, keeping the launched sound clear. A slightly sloped ceiling towards the back of the seating area compresses the sound coming from the front making it louder for people sitting further away, which is good, too.

A slightly sloped ceiling still keeps the sound of congregational singing within the congregation, where it belongs, just like a flat ceiling does, which is good. Flat ceilings are not good, though. All sounds that hit the flat ceiling are reflected back down to the floor at the same time. The timing for floor-ceiling reflections is the same everywhere in the church. This creates a horrible droning tone problem.

Circular Wall Design:Usually the walls of churches are curved, mostly in a circular manner. There are two problems with circular sound reflecting surfaces. One is that sound travels very well around the curve of the wall. The other is that sound that starts from a location out somewhere in front of the curve gets reflected back to a focal point, something like a magnifying glass. The location of that focal point moves around, depending on where the sound source moves or is located. Refocused echoes are very loud at the focal point and when you hear it, the sound seems to come from some mysterious place, some odd direction which usually doesn’t make any sense. When working with churches and most public spaces, the sound reflecting

wall is never completely covered with absorption. This causes a “dead acoustic” effect that is very undesirable for people to hear. However, the focusing effect of curved walls is so strong that applying a “normal” amount of sound absorption to the wall barely effects the sound at the focal point. One then adds more and then more again until you find the wall to be completely absorptive. The focal point problem went away but now we have the “dead wall” effect, also a disagreeable sonic effect.

When working with curved walls, the thinning effect of absorption is not enough. Here, two different acoustic functions are needed to get the job done.1) Some of the sound needs to be absorbed at the surface of the curved wall, as with any back wall.2) The remaining sound needs to be scattered, reflected in directions away from the focal point.Whatever sound that is not absorbed on the curved wall needs to be scattered off in some direction away from the focal point. The typical sound scattering device is a curved panel, called a poly. The poly panel is essentially a thin flat panel that is bent to have a curvature that is reversed to the curve of the wall. A poly only scatters mid and high range sound. The poly must also be a bass trap so that the reflecting low frequencies do not focus. By mixing up the absorption and scattering of sound on curved surfaces, people sitting near the wall still hear a lively wall and those near the focal point don’t hear the focused sound. Both seating areas are now comfortable.

Role of Beams in Church:Large churches have big ceilings and are at considerable height and to support such ceilings big beams are needed. The beams are so big that they really reflect the sound that hits them. Speakers are usually hung in the ceiling, nested up inside of or just below these big beams. The beams catch the sound emitted from the speakers and redirect it, usually in the wrong direction. Big beams can be big trouble in churches. Beams restrict the free expansion of sound in the room and when the sound gets trapped between a pair of beams and travels down their length, the sound between the beams remains very loud. Reflection of sound between beams also creates a reverberant effect overhead, right by the speaker. This reverberation isn’t like the more familiar, room reverberation which takes around 2 seconds to build up strength. This cross-beam type of reverberation is very strong and takes place very fast. So fast, people can’t separate the cross-beam reverberation from the voice of the speaker.

There is only one way to deal with bad acoustics from big beams and that is to add sound absorbing material to the beams, way up there. If the acoustic fabric has a similar color, close to the beams, no one notices the acoustic material that has been added to the hall. When it comes to church acoustics, the best opportunity for success is a design that incorporates easily, that no one would notice and that works. The way the church looks is important to people, and usually they are resistant to changing the aesthetics to a large degree.

Role of floorings:In order to strike a balance between the requirement of musical purposes and speech purposes the church hall should be designed with a fine blend of reflection and absorption of sound. Absorption of sound is taken care by absorbing material on walls and beams. For reflection purposes floor is made of marbles so as to maintain a balance between clarity of speech and a quality classical music experience.

Acoustics of a Buddhist Temple• The types of prayers conducted in a monastery are low frequency chants.

• One of the aspects of human hearing is that we will perceive a progressive loss of bass (lower) frequencies as sound intensity decreases according to inverse square law, as is the case if we move away from a sound source; this is called as “bass loss problem”.

• This is the result of natural discrimination by human ears for lower frequency as sound intensity decreases.

• This problem can be overcome by increasing reverberation time for low frequencies than those of high frequencies.

The graph shows a progression to higher reverberation times for low frequencies. It is typical for the reverberation time for low frequencies to be some 30% higher than the overall average reverberation time. This characteristic helps to deal with the bass loss problem.

• Actually, the longer reverberation time for lows usually happens naturally, particularly if a lot of wood, curtains or any other sound absorbing material is used in the construction since these materials absorb high frequencies more than lows.

• Thus we can find that Buddhist monastery is usually filled with sound absorbing materials like wooden floors and ceilings, silk curtains, tables with cloths.

Study of a Japanese Buddhist TempleArchitectural acoustics of a Buddhist Temple is similar to string instruments in western music. The altar (hard table, also known as the Lord’s Table) of the temple is a hard reflecting board that is coated with Japanese lacquer and

polished similar to the surface of a violin. The bottom side of this is supported by a sound post from the basement also similar to the western string instruments. The altar is pushed from the top as well as from the bottom. This keeps the altar under many stresses. Although the details are not known, this is supposed to contribute to the acoustics of the wooden temple.

Location of speaker (sound sources)

Sources S1, S4 and S4’ are located along the central axis and are known as the symmetry keeping positions. On the other hand, S2 and S3 are having asymmetric positions. S1 and S4 are the positions of the ‘tuning monks’ whose singing is followed by the rest of the people in the temple. S4 is used for regular purposes.

Sound measurements were taken by ten receiver microphones positioned at the locations shown in the figure above. The sound levels and reverberation times were plotted against octave band frequencies for different sources and receivers.

‘River’ between ‘live’ and ‘dead’

Aisle- Live region for monks and ordinary people

Altar- Dead region

Sound levels and reverberation times for sources S1, 2, 3 and 4.

We can observe that the sound levels are higher in the low frequency and also the reverberation times are lower at low frequencies. Reverberation time is around 0.4-0.6 sec. It can also be seen for S4 (tuning monk’s speaker) that the sound levels are higher in the live area (area for monks and other people), shown in blue lines, and the reverberation times are higher in very low and very high frequencies. This gives a better enchanting experience to the people in the temple.

The asymmetric location of S3 has also shown to contribute to the prayer environment, especially at high frequencies. This suggests that breaking of symmetry can give desired results in the acoustics of a prayer hall.

Comparison between Monastery, church and Concert hallsFormula used:

Clarity index : Cexp = 10 log [exp(1.104/RT) – 1] dB

Strength : G = 10 log (RT/V) + 45 dB

From calculating these values we can make distinction among the church, Buddhist monastery, and a concert hall and make a comment on the preferential use of these buildings.

T60 Clarity Strength Comments

Monastery Low High High Ideal factors for speech and preaching purpose and chanting

Church High Low High Good conditions for choir singing as well as strength for preaching

Concert hall Medium Medium Low Designed by keeping everything in mind

References:1) http://www.sae.edu/reference_material/pages/Coefficient%20Chart.htm, Date: 17/4/14. Time: 5:34 pm

2) The holiest Sacred Heart’s Church, Assessing the acoustic properties of Roman Catholic churches: A new Approach- Krzysztof Kosała & Zbigniew Witold Engel. Date-18/04/2014 time-7.27pm

3) Aichi Prefectural Art theatre- http://www.aac.pref.aichi.jp/english/gekijyo/guide/c_holeg.html Date-18/04/2014 time-7.27pm

4) Beijing temple of heavens- http://www.chinatour360.com/beijing/temple-heaven01.htm, Date-18/04/2014 time-7.27pm

5) http://www.religiousproductnews.com/articles/2009-February/Supplement/Room-Acoustics-and-Worship-Space-Design.htm

6) Concert Hall Sound Clarity: A Comparison of Auditory Judgments and Objective Measures, Andrzej MIŚKIEWICZ, Tomira ROGALA, Teresa ROŚCISZEWSKA,Tomasz RUDZKI, Tadeusz FIDECKI.

7) Broken Symmetry of Spatial and Temporal Design in Japanese Temple Ken ITO, Ryota SHIMOKURA, Yoshiharu SOETA, Tomohiro OHSAWA, Shin-ichi SATO, Yoichi ANDO