Acoustics: Balcony Faces and Mud

In Uncategorizedby tfwm

There have been quite a few articles over the years addressing the acoustical environment in houses of worship. This article will describe some more specific—and common—problems and discuss what can be done to fix them.

Did you know that one of the most common causes of poor speech intelligibility in houses of worship and auditoriums is a hard balcony face?

Balconies come in different forms. They often involve a face that juts into the main space and over the main floor seating areas. Reflections from this surface have the potential to cause some pesky problems. Figure 1 illustrates a sound reflection from a basic, flat balcony face. Loudspeakers are often “flown” over the chancel area and point down in a manner that best covers the main seating areas with sound. Unfortunately, mid to high frequency sound can strike the face of the balcony and subsequently arrive at listeners’ ears at a sound level that can cause some serious problems with the communication of speech. The areas where this is the biggest problem are often the “best seats in the house”! (Note the diagram showing the reflection “beam”—the shaded gray area—arriving at the front five rows.)

To determine whether this is a potential problem, the distances need to be looked at carefully. Surmising the distances translates directly into the timing of the reflections relative to the direct sound coming from the loudspeakers. The relative distances between the loudspeakers, the listeners’ ears and the balcony face will dictate whether or not this is (or is going to be) a problem. The angle of the balcony face, what it’s made of (e.g., gypsum wallboard, glass, etc.), and whether or not it’s flat will also affect the severity of the problem. Figure 1 shows a simple calculation that can be used to figure out the timing of the reflection. If D is less than 23 feet, there shouldn’t be any major problems with the reflection. If D is between 23 and 50 feet, the reflection could be a problem for some listeners—some treatment should probably be considered. If D is over 50 feet, treatment of the balcony face is going to be mandatory since everyone in a certain area of the front seats is going to wonder what that sound is coming from behind them. That’s what late-arriving strong reflections do: They distract people. The threat response kicks in and some folks might even be inclined to look behind them to ascertain whether there is a large predator coming at them from the back of the church. Not good.

Add to that, certain passages of speech will become more difficult to understand. This is especially the case with curved balcony faces which are more inclined to focus a whole array of reflections at certain seating areas, all arriving at listeners’ ears very close together. If your church is in the design phase, curved, concave surfaces of any sort should be completely avoided.

In one sanctuary I visited, there were two strong reflections from a balcony face arriving in a certain seating area. The reflections were spaced out in time from each other— and from the direct sound— such that the net result was the (very convincing) aural illusion of three distinct sound sources. Suddenly, the soloist is a trio and Sunday’s sermon is complete nonsense. Not good either.

This problem can be fixed using several techniques. The simplest approach is acoustically absorptive material or panels covering the entire balcony face. These materials can be chosen to fit the aesthetics of the worship space. There are many different styles of acoustical treatment available (see Figure 2). As long as the thickness of the absorbent material is at least about 2”, you can be sure that you’re addressing the entire range of frequencies that might be bouncing off the hard balcony face. And since the area of the balcony face is insignificant compared to the total surface area of all the rest of the room’s surfaces, there is very little risk of making the room “too dead” by only treating the balcony face. The only result should be improved clarity and intelligibility at those front seating areas.

There are other options. If aesthetically acceptable, a balcony face can be removed and replaced with a railing. This sort of arrangement will allow sound to pass through and be absorbed by the seats and people behind.

If the worship space is still in the design phase, an angled or architecturally sculpted balcony face can be considered. The only bad side-effect of an angled balcony face is that care should be taken not to simply redirect the reflections to some other seating area, or to the chancel area.

Finally, commercial acoustical diffusors (see Figure 3) can also help considerably. These devices redirect and spread out sound energy, removing strong reflections and replacing them with many weak ones. Again, there are many design options available from an interior design perspective and most commercial diffusors—such as those shown in Figure 3—are paintable to match any color scheme.

Another common problem as the popularity of the contemporary worship service continues to grow is “mud.” No, I’m not talking about what patrons track in on the carpet after spending some time in the contemplation glade. I’m talking about “boomy,” “rumbly,” “thumpy,” over-powering, “sounds-like-Beelzebub-is-in-the-house,” mud; also known as the build up of low frequency sound. The bass guitarist might love the fact that his rig is causing massive deflection in the stained glass windows, but the congregation as a whole may not share this appreciation for atmospheric modulation. For a long time, the best “fix” to this problem was “turn it down” or “roll it off.” That is all changing now as new developments in affordable acoustical treatment products are able to specifically address this problem.

There are also custom-tuned panels available that are designed to knock down the low frequency reverberation (the “mud”), without removing too much high frequency sound. The high frequency stuff is what makes music nice to listen too. The build up of the low frequency stuff is what makes people say, “The band is extremely gifted, but the sound is terrible.” These tuned panels can target specific ranges of frequency that remove “mud” and their appearance is no different from that of an ordinary acoustical panel (e.g., the upper left of Figure 2). They can be incorporated into a design using other mid and high frequency absorbers, such as those shown in Figure 2. The latter can even be used directly over the tuned panels for a truly unique look.

In my experience, any worship space has a very high probability of experiencing at least one of the above problems. From the standpoint of the worship experience, either (or both) of these problems would distract people, potentially making their worship experience less meaningful. Thankfully, there are solutions that work and don’t cost a fortune.

There is a very popular article about house of worship acoustics that I like to forward to people asking how they can improve the sound of their space. The title of the article is “Why Churches Buy Three Sound Systems, and How You Can Buy Only One,” by Jim Brown from Audio Systems Group, Inc. I will conclude with a great quote from this article, available for free download through our House of Worship FAQ page—

“Careful sound system design and enough money CAN provide good speech intelligibility in almost any space. But there is NOTHING that can be done with a sound system to improve the sound of the praise band in a bad acoustic environment beyond overpowering it with carefully focused energy.”