Unfortunately, the "what did you say?" factorthe inability to have good speech intelligibility during meetings and gatheringsis all too common in worship facility meeting/conference room design. The reason is because the desired acoustical environment is oftentimes overlooked during room design. For a meeting/conference room to achieve its purpose, the room design needs to include an acoustical design that specifically addresses these items:
Good speech/hearing intelligibility
Proper acoustical treatment (what and where)
Removing reverberant echoes
Eliminating potential fault areas (HVAC noise, etc.)
Some say that in the beginning, there was perfect sound. Then man invented rooms and forever made it challenging to achieve good sound. Sound waves emanate from their sources and strike room boundaries; these sound waves bounce off the walls, ceilings and floors and get reflected back into the room, mixing with the sounds bouncing from other directions as well. This bombardment of reflected sounds is what makes it hard to distinguish what's being spoken.
Controlling this reflected sound is the key to making a room sound better. With proper acoustical design and treatment, a bad sounding room can yield excellent acoustics.
The human ear (undamaged) is so sensitive that we can detect sounds that displace the eardrum by roughly the diameter of a hydrogen molecule (very, very small). The ancient Greek theaters were known for almost magical speech acoustics. One can hear a coin drop from the farthest seats in the theater at Epidaurus. How is this possible? The answer is that no audible sound covers up the sound of the coin striking the stoneand so it is heard.
This means that background noise determines the softest sound that a speaker can effectively utilize. Even in a room that most people would consider quiet, our ears pick up all of the sound when people talk. Not only does the ear hear direct sound, but also the echo sound reflected from the ceiling and walls, and any background noise in the room. Such "noise" directly affects speech clarity. And, while the human ear can filter out unwanted noise, the end result is hearing stress and added difficulty in understanding what is being said.
Hard room surfaces are responsible for most detrimental reflectionsreflections that directly affect the achievement of good speech intelligibility. Each time a sound wave hits a surface, some of it is absorbed and some reflected. The surface's ability to absorb sound waves directly affects the amount of echo in the room. The greater the reflections are in a meeting room, the less clarity of speech.
Additionally, noise can come from the HVAC system, projector fans, or outside traffic. So, good speech intelligibility in a meeting room is determined by elimination of the potential fault areas and reverberation echoes. If the room is not properly acoustically treated, the "what did you say?" factor, or "participant ear fatigue" factor, comes into play. Have you experienced meetings where you are working so hard to understand what is being said that you end up physically tired at the end? Obviously the degree of ear fatigue varies depending on the person. Background noise in meeting rooms should not exceed 30 dB. And as an aside, it should not exceed 35 dB in offices.
When Northwoods Community Church in Peoria, Illinois, built Phase II of their facility in 2001, it included a meeting room that could easily seat 100 people. Yet, during staff meetings, it was impossible to understand what a person 10 feet from you was saying, due to the poor acoustical environment of the room. Adding acoustical panels to the walls of the room eliminated the problem, and made it a usable space.
In smaller meeting rooms (six to eight people), a good solution is to install a sound-absorbing ceiling in the form of mineral wool-coated tiles. If that is not possible, or if the room requires further improvement, deep fold curtains or acoustic wall panels can be installed. In meeting rooms where glass is heavily applied, the room may deliver an unfortunate reflection between the parallel surfaces. The best approach here is to have a sound absorbing ceiling and properly placed sound absorbing wall panels.
Larger meeting/conference rooms (for 35 to 50 people) can be more difficult to acoustically treat correctly. Here, it is best to consult with an acoustic expert.
Eliminating Potential Fault Areas
Potential fault areas include in-room noise sources like projector fans, the HVAC and lighting systems, or outside generators such as traffic and airplanes flying overhead. Today there are excellent ways to eliminate in-room noise sources. These include "silent" mechanical systems, noiseless lighting fixture ballasts, remotely located dimmer panel boards and quieter projectors placed in an acoustically treated, well-ventilated enclosure.
Room location is also important. For example, in a meeting/conference room located next to a large mechanical room producing a constant low-frequency rumble, the meeting room has significant disadvantages. Room location should take into consideration all potential fault areas including such things as heavy traffic outside the room and street traffic noise.
Another example is a meeting/conference room with four glass walls, a metal ceiling and tile floor. Potential acoustic solutions are to add carpet to the floor, hang absorbers from the ceiling, and/or add curtains inside the glass walls. In this example, speech intelligibility is all about priorities. Is the goal to be able to see outside the room, or to have a good conversation and a successful meeting without distraction?
As a side note, suspended ceilings with acoustic tiles have proven to be excellent in helping reduce the sound reflections in a room.
Room Furnishing and Décor
Meeting rooms typically contain furnishings to help break up sound. Tables, chairs, wall décor and other cabinetry can help, but should not be considered acoustical treatment in the true sense. Furniture generally provides variation in any size room to break up the sound waves. Wall décor also helps to make the room sound a little better. It should be noted that soft chairs are preferable both from a comfort standpoint and because an empty soft chair will not add as many reflections to a room as an empty hard chair. Hard surface conference and meeting tables can be a big challenge. The key is to have ample acoustical treatment above the table on the ceiling.
Class-A Acoustic Treatment Solutions
In many worship facility meeting room applications, the design, look and feel of the room is just as important as the acoustic quality. For such applications, custom fabric-wrapped, Class-A, fire-rated (ASTM E84) glass fiber treatments work best. These treatments are available as either all stretched-fabric systems or as a set of mounted fabric-wrapped panels.
A full-wall, stretched-fabric system consists of pre-engineered treatment componentsappropriate acoustical materials placed where needed in the room and hidden by floor-to-ceiling stretched fabric mounted to a retention channel. This option provides the most color and style choices, and does not restrict the use of wall space for art or other design elements. The look of the room can be easily updated without replacement of the entire acoustical treatment. While the flexibility of a full-wall, stretched-fabric system can save money in the long run, it is the most expensive acoustical treatment option. It is usually custom fabricated to the specifications of the room, often on-site. For a 40-foot by 30-foot by 12-foot meeting room, the cost for a full-wall, stretched fabric wrapped solution will range from $25,000 to $50,000.
A lower cost alterative is fabric-covered, acoustically absorptive panels designed to absorb reflected sound energy. These can be used either as a full-wall system, or as various decorative patterns throughout the room. They are made of Class-A rated acoustically absorptive core and wrapped in acoustically transparent fabric. They are specifically designed to absorb sound energy. Fabric-wrapped panels are available in a variety of finishes, styles and colors that can be arranged in hundreds of combinations. The standard thickness is typically one inch, but thicker panels are available to provide more low frequency absorption, which is important in rooms with more critical acoustical requirements, e.g., watching videos or DVDs.
Panel treatments do not allow for easy redecoration, but unlike stretched-fabric treatments, they can be removed and reused in another location without damage to the wall. For a 40-foot by 30-foot by 12-foot room, panel treatment installation costs will range from $5,000 to $10,000.
Noise Reduction Coefficients
The absorptive effectiveness of a sound absorber can be judged by its NRC (Noise Reduction Coefficient). The NRC rating is an average of how absorptive a material is in the four frequency bands considered most important for speech (250, 500, 1,000 and 2,000 Hz). In general, the NRC can be used to compare absorbers; the higher the NRC, the more sound is absorbed in the speech range. Note that there is no absolute number that indicates total absorption, so it is possible to have an absorption device rating well over NRC 1.00. This simply indicates that a device or material is a very good absorber. Also note that for more critical applications, the performance of an absorber in the individual frequency bands should be compared.
For a custom full-wall, stretched-fabric system it is not possible to get an overall NRC rating because a variety of absorption materials are used. The glass fiber panels wrapped in an acoustically transparent fabric typically have an NRC rating of 0.80 or better (the preferred rating for absorbers). This is usually the minimum requirement for an absorber used in a tele- or video-conferencing room.
Importance of Expert Help
To ensure excellent speech intelligibility, it is important to use a professional consultant who can diagnose problems and recommend solutions. A good acoustic consultant will consider sound absorbed by people in the room, sound diffusion from decorative surfaces, and will calculate the exact number, size, thickness and placement of the appropriate types of panels.
There are several ways to find acoustical consultants. Check the official website of the National Council of Acoustical Consultants (www.ncac.com), and/or the Acoustical Society of America (www.acoustics.org). Or, just ask aroundchances are another church in your community can provide a great referral.
Acousticsspecifically, reducing the "What did you say?" factormust be considered an integral part of any worship facility conference room design.