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Improving Sanctuary Acoustics
By: Thom Mullins

"We'll make it look so good they won't care what it sounds like" was the comment made to me by an architect once at the beginning of the design of a new worship facility. 

While that may be true in a very limited number of cases, that is not the expectation of most worshippers and pastors. We are inspired by the sights and sounds of the sanctuary, and our communion with one another during the service. Good sanctuary acoustics are critical to our worship experience. Unfortunately, a hard lesson was learned the congregation was just as interested in hearing the Word as they were inspired to worship by the architectural design of the space.

Tackling the issue of improving acoustics in worship spaces in a short article such as this leaves me open to accusations from my fellow acoustical consultants of over-simplification of the issues involved and a willingness to leave the child in the toy store without adult supervision. After all, the modern study of room acoustics began just over a century ago. 

Prior to that time, acoustical "design" occurred almost by accident. The Greeks started it  all off by noticing that the spoken word was easier to hear if you stood in front of the person speaking. They paid attention to local hillsides and other areas where it was easy to hear someone speak. Then they started adding stages and proscenia; soon roofs and walls were needed to protect people from the environment and to keep the producer from losing drachmas as a result of rain. Then there was a gap of about a millennium where not much progress was made, and new buildings for performance or worship were not constructed. Slowly, the modern theatre and house of worship developed over the centuries, each affected by the perceptions of what made a space suitable for a particular purpose. Fortunately, there were "good" accidents and there were "bad" accidents, both of which allow us to apply the lessons learned from our successes and failures to new projects. Since those beginnings, enough has been written about what we have learned to fill small libraries. 

Before we proceed with our discussion of improving sanctuary acoustics, let us define a few terms. 

We typically start off talking about "reverberation time" a term that refers to the amount of time it takes for sound in a room to decay by a specific amount; it is expressed in seconds. The optimum reverberation time in a space depends on a number of factors, including the style of worship and the need for speech clarity between the presenters and listeners. It is determined by the cubic volume of a room and the reflectivity of the room surfaces, and is typically controlled by the amount and placement of absorptive or diffusive surfaces in a room. When you add absorption to a room, you're effectively soaking up acoustic energy and removing it from the environment. The reverberation time is reduced.

Diffusion is just the opposite of absorption. It scatters or spreads the acoustic energy in the room around to make better use of that energy. The reverberation time stays the same or it may appear to increase. A reverberation time for music of about 2.0 seconds is widely preferred by most listeners, for most types of music, with a range of 1.5 to 2.5 seconds as equally acceptable. In larger cathedral spaces, this time may be 4 to 6 seconds, or more. Reverberation times that are acceptable for speech may range from 1.0 to 1.5 seconds.

You'll also hear about "noise criteria" or "NC levels." This is a measure of the loudness of background noise (usually unwanted noise) in an environment. Major contributors to NC measurements in a room might include traffic or airplane noise from outside a building, or from the hallway outside the sanctuary, heating and cooling systems, and lighting ballasts.  The goal here is to reduce this intrusive noise to an acceptable level. 

These are the basics. Any work done to improve sanctuary acoustics ultimately must address reverberation time, the control of reverberation time through the application of absorptive and/or diffusive elements, and achieving appropriate levels of background noise.

So what are the really important items in a good, or even great, acoustical environment?

  • Music and speech are loud and clear.
  • The sound is full and rich, not weak
  • Listeners easily perceive a sense of spaciousness in the sanctuary.  This is something you don't hear out of doors or in rooms with heavy drapes and full carpeting.
  • There are no distinct echoes.
  • There is a balance in tone and volume between the instruments and the vocalists.
  • The background noise is low. Ventilation and heating fans, lighting dimmers and outdoor noise are nearly inaudible.

    Worship style has a tremendous impact on room acoustics, one that few people understand. Reverberation times in large liturgical churches tend to be longer, emphasizing the community aspect of worship and promoting a strong sense of reverence and awe. Longer reverberation times help to blend the voices of the choir and the congregation into a full, rich sound that surrounds the listener. This is a direct result of the room finishes harder and less absorptive.

    More contemporary worship services and environments tend to benefit from more absorptive room finishes, creating shorter reverberation times. This is due to the extensive use of amplified instruments and voices. The additional absorption tends to quiet these instruments and helps to bring clarity to what is being sung or said, thus improving the worship experience.

    One of the main problems arises when a liturgical church decides to add a contemporary service. Complaints of the music being too loud or the lyrics and sermon being unintelligible are common in these cases, both a direct result of a (typically) longer reverberation time. These can be overcome by judicious placement of absorptive or diffusive elements in the sanctuary and at the altar. 

    As in the rest of life, a balance is important. I can think of no worship spaces on the extreme ends of the continuum between a totally reflective space and a completely absorptive space. The trick is to find the balance that provides the best fit for your environment. 

    Absorption can be added throughout a room to lower the overall reverberation time in a space, or it can be added near a source that is too loud in an effort to reduce the sound at the source. 

    When added throughout a room, the goal is to lower the overall reverberation time, which improves the intelligibility of speech in the room. When added in a specific location, it is more often used to reduce the sound level of a specific instrument or to reduce the echo coming from a specific reflecting surface. 

    This is done quite often with acoustic drum sets by placing a short absorptive "gobo" around the front of the drum kit. 

    Another example is the contemporary worship service where the congregation complains that they hear more from the stage monitors than from the main sound system. Many times, the wall behind the worship team is hard and reflective, and reflects sound out into the congregation. It isn't unusual to hear from the worship team that they are unable to hear one another play it's too loud on the stage. So they turn up their instruments and the monitors to compensate, which exacerbates the problem.

    The best solution here would be to add absorption behind the worship team. This solution could take the form of architectural wall panels or a thick drapery. Mixing absorption with diffusion above the team will improve their sense of ensemble. The result is a lower sound level on the platform and more control over the main mix. 

    You may also experience problems with the shape of the sanctuary that affect the acoustic quality of the space. This can take several forms. 

    One common issue is a surface or series of surfaces focusing sound into the congregation or back towards the pastor or worship team. This results in a false sound source that arrives later at the listener's ears, creating a "muddy" or indistinct sound. If the surface is far enough away, this focusing could arrive so much later than the original source that it sounds like a distinct echo, which can be very confusing for the pastor or the worship team. 

    The solution here would be to redirect the sound by adding diffusive elements to the surfaces in an effort to redirect the sound. This would be a useful solution where a balcony face is the culprit. Breaking up the surface of the balcony by adding facets to the surface will help. The situation may dictate adding absorption to a larger surface area in an effort to reduce the level of any reflections or echoes coming from that surface.

    You should also consider the source of the echo. If the sound wave from a loudspeaker is creating the problem, have the contractor re-orient the loudspeaker to shift the reflection to another less critical location. 

    Such difficulties can also be caused by a curved wall (the typical culprit), although I have experienced this problem in a church that met in a converted warehouse facility. The loudspeakers, although aimed correctly, were hitting the large flat wall at the back of the room. This sent distinct reflections back towards the pulpit that could be distinctly heard by the pastor and the worship leader. The solution in this instance was a combination of absorptive and diffusive elements applied to the wall. The reverberation time in the space was acceptable for the worship style, so a minimal amount of absorption was required.  The diffusive surfaces that were added redirected the sound across the congregation at a much lower level than the discrete reflections they had suffered with before these changes were made. 

    This raises a completely legitimate question whether to use absorption or diffusion.  I hate to say "It depends," but that is really the best answer, as shown in some of the examples I have used. 

    If the reverberation time is adequate or too low for the space and the style of worship, it would be appropriate to consider adding diffusion to a room. If the reverberation time is too long, additional absorption is likely in order. A good answer to this question in a particular room requires detailed knowledge of a space, how it is used, and the specific problems being experienced. 

    Do people complain that they can't hear and understand what is being sung or said? Do the complaints cluster in a certain section of the sanctuary? Have you just made a change in the style of worship or upgraded your sound system? Do the problems appear to be age-related? A good solution will entail listening and asking questions and will involve some testing, analysis and design by a qualified acoustical consultant. 

    With strengthened acoustics, both reverberant and spacious and in the absence of distracting noise music and spoken voice will fully realize their emotional power, which has always played a significant role in any congregation's worship experience.

    Thom Mullins is a senior consultant with BRC Acoustics & Technology Consulting.

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