Combatting common acoustic hurdlesAudio/Visual, FEATURE STORIES, TECHNOLOGY Monday, December 2nd, 2013
By Eric Smith
The congregation can’t heed The Word if it can’t hear The Word!
Every sanctuary has its own set of acoustical challenges presented by two main factors: the type and format of musical accompaniment in the service, and the shape, construction and layout of the sanctuary itself. These challenges range from poor speech intelligibility during standard verbal communication, to uncontrolled sound energy during praise band performances.
In large sanctuaries, high levels of reverberation, or echoes, cause poor speech intelligibility. Echoes are caused by sound waves reflecting off reflective surfaces, and can cause speech and music to sound garbled and lyrics inaudible.
Reflected sound is inherently inaccurate sound. Why? Because it will inherently differ in arrival time, compared to the original sound. And, it will never have exactly the same frequency content as the original sound. Reflected sound that arrives within the critical, very short period after the original, direct sound is detrimental and must be dealt with if we’re to hear accurately in our rooms. This includes both lateral and vertical reflections, despite some people’s contentions.
Proper acoustical treatment gives you a clean initial time delay (known as the ITD — the period between the direct sound and the beginning of the reflected sound) by especially controlling early reflections that come from the nearest room boundaries. Without proper acoustics, you’re not giving your ear/brain mechanism the time it needs to latch onto the original, direct sound. Even though your ear/brain mechanism can “learn” an improperly treated or untreated room over time, it will always have to siphon off its processing abilities (CPU cycles, if you will) to process the poor acoustics.
This degrades one’s focus and will be a detriment to a proper listening experience.
Many houses of worship have difficulty controlling reflected sound. While there are many specific causes of unwanted reflected sound, it can be controlled through the absorption and diffusion of this sound energy. The solution to your acoustical problems may require one or both.
Absorption of sound waves can be accomplished through common room features, such as curtains, carpet — even the congregation. Adding padding to pews or seating is a good way to provide an accurate acoustic environment. And, because a well-padded seat provides roughly the same absorption as a person, that environment is maintained regardless of whether it’s a packed house or a small rehearsal.
Diffusion is provided by anything that breaks up a flat surface and directs sound waves in different directions. The placement of wall décor (window trim and statuettes, for example) are sometimes enough to provide adequate diffusion, depending on the style of worship.
While common room features might help control acoustic anomalies, acoustic panels are usually needed to properly treat a house of worship. To this end, our company offers fabric-covered fiberglass panels in virtually unlimited sizes, thicknesses and finished appearances. This type of absorber “dries out” a room by absorbing and trapping sound energy in its specialized fiberglass core, improving overall intelligibility by eliminating the echoes that could muddy speech or music.
Control the sound in your house of worship so the message is clear! Proper intelligibility and balance keep worshipers in the pews and allow them to absorb more of the important messages you’re conveying.
Eric Smith is the founder and president of Auralex [auralex.com] in Indianapolis.
Auditorium acoustics, revisted
By Nick Colleran
These sacred spaces present a host of acoustical challenges, depending on their layout and design.
It has been said that whenever someone invents a better mousetrap, a better mouse isn’t far behind. To that end, this author has noticed that whenever something is “common knowledge,” some uncommon problems soon follow.
Case in point: It’s well-known that an auditorium works best when it’s deep rather than wide. This allows the room sound to develop and envelope the audience while using the reflectivity of the side walls to engulf them with sound.
With the walls far apart and the rear wall closer, two things happen: Sound returns from the back wall at higher intensity — and usually out of sync with the music — while overlapping the spoken word. When the reverend repeats, it reinforces his message with added emphasis, while any room repeats usually overlap and obscure the message.
Shallow versus deep spaces
If your auditorium hasn’t been built yet, you can build a room that’s more conducive to intelligibility, with close to a three-to-one ratio of depth to width. If you’ve seen and heard a good-sounding room, it can be copied, if not necessarily scaled.
By definition, scaling a room to a smaller size produces shorter wavelengths between walls and a different set of reinforcing and canceling frequencies. If the balcony is lowered, it creates an “acoustic shadow” below, requiring delayed sound reinforcement.
Any artificial delay should always be at a lower volume and slightly later in arrival time to keep attention focused toward the natural sound source. (Like a well-designed subwoofer, it should only be obvious when it’s turned off.) With the balcony lowered, sound may now bounce off its face, which is now in the path of the primary speaker array.
The value of speed bumps
If you already have a shallow room — or one that’s circular or near-circular, such as an octagon or hexagon — acoustic soundness is more of a challenge. In some large dome venues, sound can be heard racing around the perimeter. This “race” can be slowed by installing acoustical speed bumps, such as hollow, half-round broadband absorbers. They are also effective on balcony facings to abate slap-back to the stage.
If you have a dome-shaped sanctuary, ceiling clouds might be appropriate to reduce focus. The dome was an effective sound reinforcement technique and can be found in early 20th-century venues for acoustical performances.
Spread the sound around
Diffusion used to be built into rooms; now, acoustical devices can “fix” an existing space. For large spaces, diffusers — of the poly-cylindrical, barrel-shaped variety, for example, which also serve double-duty as bass traps — might be best for redistributing energy throughout the room and extending low-frequency absorption of fabric-covered, sound-absorbing wall panels. Without them, intelligibility might improve. But, an uncomfortable “boom” in the bottom range could remain.
Two significant points influencing amplified sound are centered on the ability to hear the sound accurately. First, a reflective, flat surface behind the mixing position will color the sound and falsely influence decisions on equalization, and so on. The phenomena can be corrected by adding binary-array wall diffusors behind the mixing position.
Second, placement of the sound mixing console below the balcony (or otherwise distant from the listening audience) can lead to excess listening levels in more remote areas of the sanctuary. If the mix area must be obscured, a visit to these areas by the audio minister during the performance should be routine. An acoustic performance area that’s over-amplified to the point of having the balcony shake is now a common scenario.
Nick Colleran is former president of Society of Professional Audio Recording Services (SPARS) and Virginia Productions Services Association (VPSA), a former recording artist and recording engineer. Today, he is a principal at Acoustics First Corporation [acousticsfirst.com] in Richmond, VA.
Is the music too loud?
By Larry Schedler
Your worship musicians are enthusiastic to express their love and praise through music; but, many sanctuaries are too small to accommodate their loud drum kits and electric guitars. In these spaces, hard, flat surrounding surfaces often cause indirect reflected sound to be distorted or focused into “hot spots.” When this happens, the congregation can get overwhelmed by the harsh loudness.
On the other hand, trying to control your musicians’ exuberance can make them feel frustrated. So, how do you keep the musicians excited and engaged — while still making sure the experience is positive and uplifting to those in the pews?
You might think, If only the drums were quieter, everyone else could turn down their volume. Someone suggests a drum shield — a set of clear acrylic panels positioned in front of and around the drums to reflect sound back and away from the audience, and out of the other stage microphones.
Remember that this reflected sound has to go somewhere. In some cases, the drum shield will divert it back into heavy drapes or wall-mounted baffles that absorb the sound. If so, problem solved!
But, if there’s a hard wall behind the drums, that sound will be reflected right back out toward the audience. This causes an even bigger issue, because now the sound is slightly delayed from the original sound. That offending sound must be muffled.
Someone suggests a wall-mounted acoustic baffle. It’s important to remember that, since sound radiates outward in all directions, the further from the source, the more square footage that will require treatment. Also, if an acoustic baffle is attached to the wall, you’ll need to check building fire codes.
Common “acoustic foam” is considerably less effective than compressed fiberglass baffles of comparable thickness. Baffles positioned close to the drums are the most acoustically efficient and cost-effective alternative.
A hard ceiling above the drums will have the same sound-reflecting problem. Plus, it’s expensive to acoustically treat. Many worship houses have both wall and ceiling issues to contend with. In these scenarios, a sound-isolation enclosure is the perfect solution.
Sometimes, electric amplifiers need attention, too. Your guitarist might demonstrate that the music just doesn’t sound right unless the amplifier is adjusted to a specific minimum loudness. If so, smaller reflective shields, baffles and enclosures are also available for amplifiers.
Larry Schedler is vice president of sales and marketing at ClearSonic Mfg., Inc. [ClearSonic.com]