Intelligibility and Acoustics Part 2: Speech Versus Music

A note from the author: Having been involved in several hundred HOW sound system projects, across many denominations, over the last three decades, I hope what I have learned as discussed below, will help you avoid the classic mistakes and poor choices I have seen far too often. Remember a worship space with bad acoustics is just a building, but a properly implemented HOW space with attention to acoustics, worship style, and most importantly the people, is a church!

It’s the Law

As a reminder, and as explained in the first article (rAVe HOW March 2017) the essential element within this topic is that no matter what you may read, be told, or have presented to you, there ARE immutable laws at work here, and no product can get around them. Keep that in mind as we proceed!

A Large Debris Field

Suffice it so say that the church sound world is littered with the debris and the wasted money created by poorly designed/executed systems or those installed into spaces that were acoustically compromised beyond any hope of intelligible reinforcement, either by their architectural design or by their interior look and feel or most often by a complex combination of both — “well… we must put the stained glass in that location…” despite the fact that they have been told, repeatedly that the chosen location will cause massive reflections from the proposed sound system.

Do not let well-meaning but acoustically-uninformed, planning make it impossible to deliver the core function of any worship space — the service.

Since architects are almost always involved (with or without liturgical design consultant services) and architectural designs/features and the needs on the acoustical side can clash it is extremely important that all parties reach a consensus very early on in the project on what compromises will be made and by whom, since most certainly some will be required. This applies regardless of whether the project is new construction, rehab or rebuild.

Therefore it is essential that all parties thoroughly understand the minimum demands required by intelligible reproduction of the spoken word or other program elements including praise music groups, organ or choir and similar worship service components.

Working With the Space

Despite the seemingly impossible-to-solve conflict between design of the building/worship space and desired functionality for the space from a sound system standpoint, it IS possible to have both. While the need for “space” or reverberation to enhance choir, organ and some musical elements cannot be ignored, it can and will happily co-exist with the spoken word, IF both elements are planned for and managed from the outset of any system development process.

For example take this church in the Toronto, Canada area.

This space allows both the spoken word and musical elements to work in harmony — because it was designed that way from the outset.

Pre-plan or Fail

For this blissful state of co-habitation to emerge, the initial analysis of the physical attributes of the chosen space or design for the space is an absolute prerequisite. Across the worship space designs I have been a part of, it is at this initial stage is where things usually go awry.

It’s All About the Reverberation Time

While there are many factors influencing a worship space’s performance, the most critical and most obvious to the congregants is reverberation time. Reverberation time is an essential and critical tool used to evaluate the acoustics of any space. At its simplest it is a measure of how long sound stays present within a space after it is made. More specifically, reverberation time (RT60) is defined as the time required for the level of sound in a room to drop 60 dB after the initial signal ends. Remember, the decibel scale is logarithmic so every change is actually much larger perceptually than the pure numbers would indicate — so a 60 dB change is huge.

Additionally, sound decay is governed by the inverse square law, which means that the perceived change varies by distance from the source as the inverse of the square of that distance. I know it sounds complicated (and it is) but there are numerous on-line reference tables to easily provide the needed data quickly — or better yet, consult with your acoustical professional who already knows this information and how to use it.

Preferred Reverberation Time

The actual, measureable, reverberation time for a space is dependent largely upon its physical volume (which is not changeable), the kind of surfaces it has and the materials used in its construction (which are changeable). For example, for speech, we normally want a relatively short reverb time. If the reverberation time is too long and/or if the speaker does not speak slowly, a listener will actually hear sound from more than one word simultaneously. The result is a muddled sound that is not easily understood.

On the other hand, if music is played within a space with a longer reverberation time, one that would be nominally less than ideal for speech, the musical notes tend to blend together, which is more pleasing than a dry dead sound. So the use of a space has a tremendous influence on what reverberation time is most desirable. It is also vital to remember that the defined usage is often not what ends up happening in the real world. The house of worship that was never going to have anything but speech all of a sudden wants to put in an organ, for example — so be careful to not only find out the current plan but also any future plans, even if vague and undefined at the outset. Knowing what might happen can help avoid disaster in the future — or at least a gigantic cost issue.

Take this space for another example — it’s a box with hard walls, glass, musicians up front and little visible treatment — do you think it will work for both the musical and spoken word portions of their service? Probably not without some remedial acoustical work to achieve a balance between the hard surfaces and the needs of the spoken word for starters. It’s a nice look and feel but perhaps not as functional acoustically.

 

On the other hand, look at this classic Baptist church. Judicious, and well integrated acoustical materials (front of choir loft for example) angled walls and minimum parallel reflective surface make for a space that will nicely accommodate both the spoken word and the choir and its musical support.

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Music and Speech

By now it should be clear that there can and usually are two desired reverberation values for any worship space if both speech and musical sources are involved.

If the worship style does not include musical sources, and the space will NEVER (remember never does not always mean never) be used for that purpose it can be optimized for a short, speech-friendly reverberation time, say 1.3 to 1.8 seconds.

However, in most cases the aforementioned compromises must be negotiated.

Thus, achieving an agreeable balance for all stakeholders between speech intelligibility and musical quality is desired. As a general rule-of-thumb for most worship styles, and spaces which incorporate some kind of sanctuary type space, a reasonable reverberation time design goal should be between 2.0 and 2.5 second for mid-frequency sound (500 to 1,000 Hz) to provide both reasonable speech intelligibility and musical quality, assuming there are no obvious hard echos or other distracting noise such as HVAC rumble.

There are relatively simple guidelines available from numerous sources on-line or from professional acousticians that show how the reverberation time within a space can be controlled by the ratio of sound-absorptive surface area to sound-reflective surface area. Here’s one example.

Speech Intelligibility

In general, to maximize speech clarity, you want to reduce the reverberation time. There are many types of acoustical treatments including: wall panels, stretch fabrics, baffles, wood and perforated metal styles, as well as many varieties of cellulose type spray-on compounds to choose from. And again the manufacturers of these materials all have online resources and often design help available. You simply have to ask.

Worship Style and Acoustical Needs

To help understand the various needs, based on worship style, let’s look at three main categories of service style and their requirements — in general. Each specific facility, denomination and culture will superimpose their own needs and preferences on these general guidelines. It is therefore important to understand exactly how the particular facility will conduct their services and what makes up that service.

Traditional

The traditional or liturgical styles of worship (in both Christian and Jewish faiths), wherein the spoken word predominates, are usually the easiest to manage acoustically; reinforcement-wise since they can tolerate reasonable reverberation time windows from approximately 1.5 to 2.5 seconds without much difficulty. However if a pipe organ is part of the facility and is used in the service, aiming towards the longer end of the scale will help blend and diffuse the organ and present a smoother sonic picture, while still allowing for clear speech — IF there are no discrete echos or bad reflections present. If such conditions exist, judicious and careful placement of absorptive materials or treatments can go a long way to mitigating the problem. But sometimes the building is just problematic and other solutions may be needed. This is when bringing in an acoustical consultant would be strongly recommended, before committing to any sound system design or install. You have to have a ‘clean acoustical slate’ to work from or the system will NEVER function acceptably.

Contemporary

The contemporary church has a service style that generally includes a praise band or other musical elements, and is often ‘theatrical’ in style. The kind of spaces these HOWs tend to gravitate towards are more performance-theater in style and shape, and more friendly to sound reinforcement since it is nominally a part of the design and readily integrated (almost expected in many cases) by the worship style and service elements.

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 longer reverb time that does not interfere too much with speech or amplified music — almost a neutral space (if such a space can be built or exist). Generally, a reverb time of 1.5 seconds is desired. A large (number of congregants and spatial volume) church can function well at as high as 1.7 seconds while smaller churches should be around 1.4 seconds. In many cases, this is an electronic church because of the use of instruments and sound reinforcement as an integral element of the service.

The Blended Style

The blended church is often both an electronic church and a traditional church combined together. It has elements of both styles, which creates a complex mix of demands both functionally and sound reinforcement wise.

Their service style often includes elements of drama, theater, conventional liturgy and high energy musical performance. With such an extensive list of requirements, a reverb time of less than 1.35 seconds is a useful starting point.

A good example can be seen in this photo of the New Beginning Worship Center, Northport, Ala., wherein the musical element is front and center.

Key Points to Plan and Consider

Fixing the acoustics after the building is built is ALWAYS expensive; getting it right before construction starts is not.
Money spent on hiring the right sound system consultant is money that will be saved when purchasing and using the sound system.

It is always cheaper and better to do it right the first time. Multiple system installs, DIY/trial and error approaches and similar methods will always be budget busters and rarely produce a viable solution. Acoustics and sound system design are applied physics, not magic. Poor acoustics and sound system performance means either that the design team made mistakes or their recommendations were not properly implemented. Good acoustics seldom happen by accident.

No sound system can remove reverberation from a space. If contemporary music will be part of the worship, reverberation must be carefully controlled. Contemporary music and traditional European music make very different and conflicting demands on room acoustics. It is quite costly (and often impractical) to provide a workable acoustic environment for both forms in the same space. Any architect who knows anything about acoustics will hire a good acoustical consultant for any significantly sized church space.

And finally, the old adage that Proper Planning Prevents Poor Performance is not just a cute phrase — it’s the truth.

Technical questions? Thoughts or comments? Email me directly — I’d be happy to chat with you. Or leave a comment below!