Its effects are commonly misunderstood. Its importance is criminally underrated. It is the first thing on the chopping block in any church install or retrofit. You guessed it — acoustics. How something that is so important and has such a tremendous impact on the performance of a sound system gets put on the chopping block is a mystery as old as time. People like us — audio geeks, audio nerds — we get it. Lay people rarely understand until it is too late.
I have been involved in several projects where acoustic treatment was the first thing to get cut from the budget. I’ve been involved in other projects where getting acoustics included in the budget at all was an uphill battle. Yet when you do it, and you do it right, people are astonished by the results.
Take my church’s new worship facility, for example. We took an existing sound system from one building, moved it into a new building with proper acoustic treatment, and people lined up to tell us how great the new system sounded. I thoroughly enjoyed telling them that it was the exact same system in a room with proper acoustic treatment. They may not have appreciated it as much as I did.
First Things First
Acoustics and the sound system go hand in hand. The two cannot be decoupled from one another. With that in mind, the first step to managing poor acoustics isn’t acoustic treatment at all, but rather loudspeaker selection, placement and aiming. Choosing loudspeakers that are suitable for the room they reside in is crucial. If you have speakers with directivity that horizontally is too wide for the room, you’ll be slamming energy off your side walls and back into the listening area, causing comb filtering and poor intelligibility. If you have loudspeakers that are too vertically wide for your room, expect to throw energy into the ceiling, onto the back wall, and back down into your listening area, causing the same negative effects. There are so many free system simulation/prediction tools available today (Meyer MAPP, L-Acoustics Soundvision, d&b ArrayCalc — to name a few) that it should be relatively easy to find speakers that provide suitable coverage for your space.
When It’s Time to Treat
This article really isn’t written for the church tech director that is building a $10 or $20 million-dollar facility. If that’s you, hire a reputable acoustician to do the design work and get down into the nitty gritty like plumbing isolation and A/C duct turbulence. For most of us, we need some relatively inexpensive acoustic fixes that can improve our room without breaking the bank.
The first question to ask is where the acoustic treatment should be placed. Examine your room and look for the most obvious areas. Hard, reflective surfaces on the side and rear walls are the low hanging fruit, and will provide the most noticeable benefit when treated. Remember that your audience plane has some built in absorption from chairs and human bodies. You can focus your absorption on the areas of the wall above your listening plane starting at six to 10 feet above floor level.
When it comes time to choose the absorption product that is right for your space, you must understand how these products are tested, rated and specified. The first piece of criteria you should understand is the term “absorption coefficient,” which measures how well a material absorbs sound that hits it. For example, an absorption coefficient of 1.0 would represent a perfect absorber, absorbing 100 percent of the sound that hits the material. An absorption coefficient of 0.5 represents 50 percent absorption.
To complicate matters, a material’s absorption coefficient — as with virtually everything about audio — is frequency dependent. When evaluating absorption material and panels, it is important to look at the absorption coefficient across the frequency spectrum. This data is often shown as a graph, or in some cases in table form. For example, you might see a table that shows a panel’s absorption coefficient for octave bands that looks something like this…
You may also see a rating called NRC, or Noise Reduction Coefficient. NRC averages the above absorption coefficients into a single number. Be wary of single number NRC ratings for absorption products, because they rarely tell the whole story by themselves. Instead, look at the individual frequency absorption coefficients to judge whether a product suits your objectives. You can see that the fictitious panel in the above table performs best at higher frequencies above 1kHz but doesn’t do well below 500Hz.
The simplest solutions for treating reflective surfaces are drapery and curtains. Reputable soft goods manufacturers such as Rose Brand provide detailed acoustical absorption specs for their products. The devil is in the details when it comes to using drapery for acoustic treatment because such products can have differing amounts of “fullness.”
A drape or curtain that is pulled flat — meaning there are no ripples in the fabric (think white cyclorama) — does not absorb sound as well as a curtain with 100 percent fullness (think main curtain in a theater). If you’re looking to use this type of product as an acoustical absorber, most ratings are based on 100 percent fullness, so plan the amount of drape accordingly.
Depending on the weight of the product, you’ll get varying results as well, especially at lower frequencies. A lightweight material such as a 12-ounce. velour will perform well above 1 kHz, with absorption coefficients above .90. Below 1 kHz the absorption coefficient drops off significantly, making it less effective in the midrange and lower frequencies. One of the less obvious benefits of using drapery for acoustic treatment is that it can be easily removed or reconfigured by placing it on traveler tracks or even simply tying it off to pipes.
If you are looking for something more permanent, and in some cases more aesthetically pleasing than drapery, acoustic absorption panels are the next possible option. Companies like Primacoustic and Perdue Acoustics have many to choose from with varying degrees of effectiveness. If you are searching of basic mid and high frequency absorption, which is the case for most people on a budget, a two-inch thick rock wool panel will be sufficient. If you need the absorption to extend lower in frequency for a boomy or muddy sounding room, a three- or even four-inch thick panel will be more suitable. Increased low frequency absorption can also be achieved by floating the panel off the wall by a few inches rather than mounting it flush to the wall.
Many acoustic product manufacturers will provide some basic design assistance if you send them drawings or a picture of your room. They can provide guidance on placement, the percentage of wall coverage required, and which specific products suit your needs. Just a 20 percent wall coverage can provide amazing results that won’t break the bank, so acoustic treatment isn’t out of reach for even the smallest churches.
Vince Lepore is the technical director at St. Luke’s United Methodist Church in Orlando and teaches live production at Full Sail University.
