Let’s face it — most of us work in less-than-ideal acoustic environments. The main sanctuary at our church has a primarily wood interior, and while it is aesthetically beautiful, it can be an acoustical challenge. Our main sanctuary is used for traditional worship, so the longer decay time is acceptable for the typical choral and orchestra performances we do in that space. Our “Contemporary Worship Space” is another story — it’s a gymnasium. Sound familiar?
I’m sure a lot of you know exactly what I’m talking about, whether you work at a church with a gym service or not. You’ve probably done gigs in rooms like this, where there is little or no acoustic treatment, four concrete block walls, and a P.A. firing into three of the four walls. Wonderful.
Acoustics are a large part of what make a system great. I’ve heard phenomenal P.A. systems in poor acoustic environments, and as you would imagine, the system sounded poor and people complained. I’ve also heard less than stellar P.A. systems in decent acoustic environments, and the engineer was able to pull off a miracle. Here are some tips for getting the most out of your room and installing some quick and effective acoustical treatments if necessary.
Loudspeaker Selection and Aiming
A huge step towards taming a poor acoustic environment comes from proper speaker selection, placement and aiming. The original sound system in our “Contemporary Worship Space” (a.k.a., gym) was an old Altec rig that was probably made before I was born. Back then, it was probably an incredible system, but the aiming was poor and was especially problematic in the vertical plane, throwing energy all over the ceiling and parts of the floor that weren’t used for seating. Eventually it was upgraded to a modern line array. Aside from vastly improved audio quality, the vertical pattern control we gained did much to manage the reflections coming off of the back wall.
Absorption Coefficient and NRC
All acoustical materials have a rating called an absorption coefficient, which is the fraction of sound that is absorbed by the material. Absorption coefficients range from 0 to 1, with 0 representing a perfectly reflective material, and 1 being a perfectly absorptive material. Like most things in audio, absorption coefficients are frequency dependent, meaning a material may be good at absorbing high frequency energy but not low frequency energy. A second common rating for acoustic absorbers is the NRC, or Noise Reduction Coefficient — a mathematical average of the individual absorption coefficients at 250, 500, 1,000 and 2,000 Hz. If you are considering acoustical treatments, look for materials that indicate the individual absorption coefficients at different frequencies, or better yet, have a graph showing absorption coefficient vs. frequency. With this data, you’ll have a much easier time gauging the actual performance of the material.
Curtains and Other Fabrics
When I first started working at my church, the Contemporary Worship service was a temporary stage at one end of the gym. There were no curtains, pipe and drapes or soft goods of any kind. The only acoustical absorbers were chairs and people, which was hardly enough to tame the room. One of the first purchases I made was 80 feet of pipe and drape to mask the gym walls on one side of the room. I made the purchase primarily for aesthetic reasons, but it had a noticeable effect on the room acoustics. Soft goods like curtains and fabrics for acoustical absorption offer several benefits. They’re relatively inexpensive and easy to modify. If you need less absorption, remove the fabric, or better yet, put it on a traveler track so it can be easily moved in and out when necessary.
Absorption Panels
If you’re looking to add more substantial absorption to a room beyond what curtain fabrics or pipe and drape might provide, you are probably going to be looking for absorption panels. Such panels come in a number of different shapes, sizes, thicknesses and fabric coverings to suit your application. When considering how to place and locate absorption panels, consider the fact that the area six feet above the floor will be somewhat absorbed by chairs and people. Don’t spend too much time or money on adding absorption that close to the floor. Instead, focus your budget on untreated areas above your listener’s heads (pictured here). These reflective surfaces are the ones that will cause the most destructive reflections back into your listening area. When calculating how many absorption panels you need, leave two to three feet between each panel and make the panels as tall as you can afford, covering as much vertical area between your listening plane and the ceiling as possible. The key is to not over-absorb by covering the entire wall surface, but rather to break up the reflective surfaces with spaced absorption panels and have some reflection back into the room.
Fire Rating
Any absorptive materials you select should be rated to meet fire code for safety purposes. Acoustical absorbers from any reputable manufacturer will have fire ratings such as Class 1 or Class A. Fabric materials often have fire ratings such as FR, IFR and DFR. Do some research before purchasing any materials to ensure you’re getting a product with an appropriate fire rating for your application.
Vince Lepore is the technical director at St. Luke’s United Methodist Church in Orlando and teaches live production at Full Sail University.
