Worship sound system design can be a daunting task. Sanctuaries often feature unique dimensions and angles to create soaring and inspiring spaces, beautiful to the eye, but a puzzle when installing a modern system that meets performance and aesthetic requirements. The complexity of church design coupled with the many options available for sound reinforcement today can lead to some unpleasant surprises for even the most experienced sound contractor.

But today’s state-of-the-art sound system/acoustic design tools in the hands of a gifted designer remove the guesswork from this integral part of delivering the worship experience, with a perfect blending of science and art.

When designing a new facility, architects often use computer renderings or scale models to ensure that clients have a clear understanding of how the finished project will look, so they can make informed decisions during the design process.

In the past, there was no way to duplicate this rendering process for the aural aspects of that same facility. Today, some professional audio companies have developed advanced computer software that can accurately predict how a sound system will perform in a space before it is installed…or even before the building is constructed!

Instead of hanging loudspeakers on a trial-and-error basis to see which model or placement is best, different speakers may be “hung” in software and moved around at the click of a mouse. This “audio virtual reality” lets you “listen to the blueprint” (the room acoustics) and system configurations through a specially-calibrated playback system in the comfort of the pastor’s office. Everyone can preview what the proposed system will sound like from any listening position within the “virtual sanctuary”, again simply by moving a mouse. Committee members and the church’s music director can hear the difference between installing wood parquet flooring in the central aisle, or thick carpeting. This ability to pre-audition the sound system allows a designer (and architect, if building changes are possible) to ensure the best possible coverage and sound quality at every pew in even the most difficult acoustical environment.

How it works

To provide an accurate model of an acoustical environment the computer requires very specific data about the real space. Accurate information is critical to identifying the unique characteristics of the space and any potential problems that may be encountered. In new construction the virtual model is built by using detailed architectural drawings and information about relevant building materials; in existing structures a qualified person gathers this same information through a detailed site survey.

Once the “virtual space” is built in the software, there are several sound system performance and acoustic attributes that can be evaluated in order to achieve the best possible results.

SPL

The first task is calculating how loud the system will be throughout the sanctuary. The modeling software calculates all factors affecting the sound pressure level (SPL) in the space: the sensitivity and directionality of the loudspeakers, the sound absorption or reflection characteristics of room surfaces, and amplifier power.

The software displays a graphic of SPL mapped onto a plan and section view of the sanctuary, with gradations of color representing the intensity of sound (from red for loud to blue for soft). The designer can manipulate the design to eliminate dead spots, adding additional speakers in different locations if needed.

Unfortunately, even though SPL levels may be adequate when you look at them on a printout, in real life sound intensity is not the same as speech intelligibility. Anyone who’s tried to understand a sermon from the back row of a great stone cathedral without the proper kind of sound reinforcement knows that too much reverberation makes it impossible to understand what’s being said, even if the sound is loud. This is where other important sound measurements come in.

RT60 Measurements

RT60 is a standard measurement of reverberation time: a short sharp sound impulse is put through speakers, and an engineer measures how many seconds it takes the reverb to diminish 60 dB. The ideal reverberation amount is somewhat subjective; a compromise needs to be struck between a long RT60 that enhances music, and a short RT60 that allows the pastor to be understood.

RT60 is calculated in advance from the room’s volume, surface areas, and the absorption coefficients of the materials used. The modeling software calculates reverb time using the acoustic characteristics that (for example) make a brick wall affect the sound differently from a carpeted floor.

Most Modeling programs come with the acoustic characteristics of many standard building materials already loaded. It calculates the reverb decay at multiple frequency bands, which is important to the final result since different materials absorb and reflect high and low frequencies differently (for example, acoustic foams absorb high frequencies, but have virtually no effect on bass). It can even calculate the sonic effect of having different numbers of people in the pews, which is a useful variable for those who want to hear what the church will sound like on Easter Sunday as well as on Super Bowl Sunday. The ability to listen to the software-generated preview is crucial since a simple printout of RT60 values doesn’t begin to convey what the sound system will actually sound like in the space.

STI Measurements

STI (Speech Transmission Index) is an objective standard of how well speech can be understood through an audio system, scored from 0.00 (unintelligible) to 1.00 (perfect). STI is a complex calculation that includes the signal-to-noise ratio, the amount of reverberation and echo, and distortion in the signal path. It measures the desired signal vs. the undesired modulations in seven different octave bands. The acoustic modeling software calculates all of these, using the specifications of the audio hardware and the architecture entered by the designer.

As with SPL, the modeling software can display a chart of STI forecasts onto the floor plan. In most areas of a good church installation, readings of 0.65 or higher are desirable.

If you’re building a new church, in addition to ensuring quality sound for word and worship, you should also be aware that good STI specs may be required to pass new fire codes in various parts of the facility before you can get an occupancy permit, because of requirements that announcements be understood in case of emergency. In the final stage of your project, if a building inspector finds STI readings below the code, you’ll be hustling to make corrections. With the modeling software, the designer can assure you that the system will meet code requirements in advance.

Acoustic Modeling and Auralization Tools in Practice

Computer software requires people with training and experience to use it well. Although one can hang “virtual speakers” anywhere in software, installers draw upon their previous experience to place the right speakers in the right place in the model, providing two or three alternatives for experimentation. Once the church has specified what they expect, a preliminary plot will be drawn, and then the real work starts.

The sound designer will first look at the results for coverage (direct field, direct/reflected and arrivals/echoes) SPL and STI as shown in the display or printout, and try a few alternatives or additions to compensate for acoustic problems. This may include additional speakers on digital delay lines for under-balcony areas, or to cover areas with different ceiling heights. Alternative system designs can be plotted out, from a bare-bones system to a no-holds barred installation, to judge the value of adding additional hardware before a purchase is made.

Once these are rendered, the audio preview will take place. No matter how good the numbers look, the auralization software often reveals audio problems that don’t show up any other way. The designer “sits” in different seats, focusing first on likely trouble spots such as transition zones between different areas of the church, or seats close to a reflecting surface. By making adjustments to speaker orientation, location and type, the designer resolves the difference between the best and worst seats in the sanctuary. Distributed speaker systems can be designed with different spacing and delay times. Because there’s no lugging of speakers up and down ladders during this process, designers are free to experiment and gain experience; many say the software has made them better designers. Calculations of amplifier power needed are easy to make, so you buy only as much power as you really need.

At this point, the sound designer can “play” the results for the architect, building committee, pastor, and music director of the church. Each can hear for themselves what the results will be, and make comments. The committee can audition alternative speaker types, power, and hanging locations, so the people with the authority to decide know exactly what the consequences of their decision will be. The manufacturer that I am employed by (Bose) is so confident in the technology that the playback demonstration is guaranteed to be an accurate representation of the final installation or the system will be removed at no cost. That’s a lot of confidence!

There have been many advances in loudspeaker design and audio electronics in the past decade, but despite this, bad sound still plagues many churches. It’s not just a matter of buying new equipment and hanging it up; it’s choosing the right equipment and designing its placement to complement the natural acoustics of the sanctuary. By using acoustic modeling, sound contractors can design a system using the same sense that will be used to judge their work after it’s installed: their ears. Designing a sound system without being able to hear the design in advance is like an architect trying to design the appearance of a room with a blindfold on. Using contractors who are trained in the use of sound system design and auralization software will save you time, money, and deliver a superior sound system that’s perfectly integrated with your church’s acoustics.