Acoustic Enhancement Systems

In Uncategorizedby tfwm

Nearly every worship space has some sort of acoustical challenge, whether it be too much acoustic energy or too little. Too much acoustical energy might be manifested as excessive reverberation or late-arriving reflections (echoes), whereas too little acoustical energy might result in too little reverberation or not enough early reflections to support congregational singing and acoustic music. Depending on the program that is taking place in the space, the room can either be too live or too dry, or have any number of other acoustical problems.

The various different areas or sections of the room might also have significant acoustical issues that are different from one another. For example, the acoustics of the stage or platform area can be too live and create problems for a worship band, or might be too dry for an orchestra or choir. Underbalcony and balcony seating areas often have very different acoustical characteristics than the main seating areas. These different acoustic environments can create a dramatically inconsistent experience depending on where you are sitting.

Different program functions work best when they happen in specific acoustical environments. For example, a classical music piece with choir and organ or a full orchestra playing worship music will require an acoustical environment that is live with a relatively long reverberation time. Conversely, a music piece that utilizes highly reinforced instruments and acoustic drums requires a relatively controlled or dry acoustic environment with a low reverberation time in order to maintain clarity and intelligibility. Preaching and drama require an environment that is conducive to good intelligibility. Rarely do the acoustical characteristics of a room work well for any one of these program functions, much less work well for all of them.

In order to provide a good worship and musical experience for people in the congregation regardless of the program or music style, designers have looked for ways to change the acoustics of any particular space to better accommodate the program. Methods to modify the acoustical characteristics of a room are often called variable acoustics. While not necessarily being the perfect solution to every acoustical problem, variable acoustics elements can definitely make a difference in the usability of a room.

Variable Acoustics
In general, there are two ways to modify the acoustical characteristics of a room by implementing some sort of variable acoustics. The first way is to start with an acoustically live room and use variable elements to absorb some of the energy via the mechanical deployment of sound absorbing materials or soft goods. These materials can be almost anything that has sound absorptive characteristics but is generally in the form of semi-rigid fabric wrapped fiberglass acoustical sound panels or the more common heavy velour curtains. While these materials provide fairly good performance for the absorption of sound, the basic room design needs to be relatively live with the variable acoustic elements used to make the room more controlled.

The other method to providing variable acoustics is to begin with a dry room and add acoustic energy to the space through some sort of electronic means. This is almost always done with a system that is completely independent from the sound reinforcement system and utilizes a series of microphones and preamplifiers, signal processor(s), amplifiers and speakers. While there are many product specific names for these systems, the manufacturers themselves agreed, during a recent meeting of the Acoustical Society of America, to refer to the technology as “Acoustic Enhancement Systems.” Acoustic enhancement systems are significantly different from sound reinforcement systems, though there are certainly common elements, namely microphones, signal processing, amplifiers and loudspeakers. The difference is how these elements are deployed and tuned and what sort of signal processing is applied.

The primary advantage to electronically variable acoustics is that changing the acoustics of the room can be accomplished easily and instantaneously, in fact, even during a performance, worship service or other event. Another advantage is that the level of acoustical flexibility can range from the dry natural performance of the room to as live as the system can reasonably provide.

Conversely, changing the acoustics through mechanical means generally cannot be done in a short period of time, often taking several hours, which does not allow for changes within the context of a single event. Also, the range of variation in the acoustical performance is quite limited when compared to the electronic system. Depending on the extent of each of the systems, cost is often comparable.

Acoustic Enhancement Systems
While Acoustic Enhancement Systems can provide a flexible electronic solution to some acoustical problems, it cannot completely solve all acoustical issues. Remember, these systems can only add acoustical energy to the room and cannot remove any problems that are inherent in the room. In order for one of these systems to properly work, the room configuration and acoustical design must be carefully coordinated with the enhancement system. For example, an electronic system will not fix problems such as low frequency build-up in the space, room modes, late arriving reflections, or excessive reverberation. Each of these issues must be carefully addressed within the realm of the natural acoustics of the space. However, when used in a space with a short reverberation time, the electronic system can be used to add reverberant energy as needed to make the room pleasing and functional for a wider variety of uses.

There are several systems that have been used in the past or are currently available. These include SIAP (System for Improved Acoustical Performance), ACS (Acoustic Control Systems), ERES (Electronic Reflected Energy System), Carmen, LARES, Level Control System’s VRAS (Variable Room Acoustics System), and Yamaha’s AFC (Active Field Control). Each of these systems uses different methodologies, hardware and processing techniques, but each has the goal of electronically modifying the acoustical characteristics of a listening or performance environment. Most of these systems use digital signal processing. All enhancement systems require a strategy to achieve sufficient gain before feedback to achieve the desired enhancement. Several techniques are employed, including:

• Directional microphones placed away from loudspeakers (several systems)
• Time variance techniques in which the delay lengths within the reverberators are varied continually (LARES, AFC)
• Time variance techniques in which only one of a set of microphones are used at any one time (AFC)
• Reverberators that are designed to enhance the power spectrum uniformly (VRAS)
• Systems that allow the use of 16 or more microphones distributed throughout the room (VRAS)

In addition, most systems provide a way to electronically add early reflections that are usually provided by reflective surfaces in a room such as the walls and ceilings. The relative balance of early reflections and reverberation enhancement is determined during the tuning process.

To this author, as well as other critical listeners, some of the systems sound more natural than others. This is of course a subjective impression, but a very important one that will often determine the usability and the success of a system. The issue of unnatural sound has been the primary complaint with early systems but has improved over time with new developments in the industry. Also, some of these systems are geared more towards performance venues where audience participation (in our case, congregational singing) is not important, where others are specifically designed to improve both the performance acoustics as well as the participation acoustics.

There are advantages and disadvantages to each of these systems, and some are newer and have had greater success than others, but again, the goal is the same. That is to add acoustical energy to the space. It’s not the purpose of this article to evaluate or endorse any of these products, but simply to discuss the design issues associated with their use.

These systems, once installed, are set up to provide acoustical enhancement for various different program functions. For example, in a room where the natural acoustics of the room are very dry, there could be a setting for preaching, a setting for highly reinforced music presentation or concerts, one for a blended music style that has additional acoustical energy in support of congregational worship, and one for acoustic music (choir, organ and orchestra). There might also be variations of each of these settings. The critical issue is to develop the settings and parameters over time that will best support the program functions. Proper tuning and adjustments are critical to the success and usability of the system.

Keep in mind that an Acoustic Enhancement System is traditionally intended to be stand-alone and independent of the sound reinforcement system. These systems are generally autonomous and intended to modify the natural acoustic environment in order to provide a flexible means of enhancing the program. However, a worship experience that incorporates drama may consider the benefits of a system that can provide support for surround sound control as well as acoustic enhancement.

Design Considerations
When considering the use of an electronic acoustic enhancement system, it is important that careful planning and coordination take place. The following are some issues to consider when implementing one of these systems:

o Hire a qualified acoustical designer to help guide the process and to develop the design of the room acoustic environment and electronic room acoustic enhancement system. It is critical that all aspects of both the natural acoustics and the electronic system are closely coordinated so that the room will perform as desired.

o Determine the program requirements for the acoustic space and list the goals for system performance and quality. Consider the purpose of the system. Is it to enhance congregational singing, change the overall acoustics of the space, enhance performance acoustics, improve certain portions of the space such as underbalcony areas, or all of these?

o Carefully evaluate each prospective system and product to make sure that it will meet the needs of a program. This is where the design professional can help guide the process. For example, if one of the primary objectives is to provide acoustic energy back into the congregation to enhance the worship experience, then it is important that the system chosen has the built-in capability for enhancing the worship and that it is not intended strictly for performance venues (concert halls). Using a system that can contribute both early reflections as well as reverberation is ideal for worship service type functions.

o Ensure that the infrastructure and aesthetic impact for the system is carefully coordinated. Make sure that microphone locations are coordinated, speaker locations are properly integrated, that A/C power and equipment accommodation for the system will be adequate, and that it all integrates with the architecture of the space.

o Never use the system to create an acoustical environment that sounds unnatural. When it sounds unnatural, the listener will subconsciously be distracted from the program that is taking place. For example, it is critical that there are no acoustical enhancement settings that would make the room sound much larger than it physically is. If your eyes and your ears don’t agree on the information being brought in, there will be a subconscious discrepancy and it will be distracting and unsettling to the listeners.

o System settings for various program functions should sound natural and should not be noticed. No one should know that there is even a system in the room that changes the acoustics. It should not be apparent that anything unnatural is happening in the room.

o Transitions between various settings need to be gradual and cannot be disruptive or noticeable. Again, the system settings can be changed even in the middle of a song, but the transitions need to be carefully planned and thought out before they happen.

o Determine the skill level of the audio staff when configuring the system. Experienced operators will be able to ‘perform’ the room acoustics throughout worship by changing settings and even reverberation level throughout the event using dedicated controllers. Churches that do not have this expertise in house may wish to use some of the built in music/speech detection systems provided with some of these systems (LARES, VRAS) to automate the operation of the enhancement system throughout the service.

The application where an electronic room acoustic enhancement system works best is with a combination of one of the newer systems that provides both early reflections and a decorrelated reverberation processor in a moderately to extremely dry room. For example, if the natural acoustics of a room were to be designed to be almost completely void of any reverberation or diffuse sound energy, one of these systems could be implemented to create a variety of different acoustical settings for various program requirements. The variations in the acoustics of the space can be almost infinitely flexible.

If a room has some significant acoustical challenges, the addition of acoustic treatments including sound absorbing panels or wall and ceiling shaping can be used to resolve the primary acoustical problems. Then an electronic room acoustic system can be added to provide additional early reflections and reverberation to the space to make the room much more accommodating for the various program functions.

The cost of these systems can range from under $100,000 for a basic system design in a simple room up to $250,000 or more for larger and more complex rooms with separate zones that might include a stage or platform area, a main floor seating area, underbalcony seating area and balcony seating area. While this type of system can be expensive as an individual item, it can still be more cost effective than drapes, panels, wall shaping and other non-electronic variable acoustic elements and will provide much greater flexibility and control of the room.

Electronic room acoustic enhancement systems will be increasingly used in future projects as the technology continues to mature and the success of these useful tools becomes more widely recognized. By their nature, if properly designed and implemented, these systems are the perfect tool for the widely varying program functions that take place in the church today.