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Improving Multimedia
By: Nick Colleran

One size may fit all for stretch socks, but it doesn't apply to sanctuary sound. When I do the occasional site visit, it becomes clear that what may be common knowledge in the acoustical community is not necessarily obvious to the folks who don't work with sound every day. Unfortunately, this sometimes holds true for those who should know better as well.

A typical case is using a tested design from an established church and applying it to another with different dimensions. Before discussing the room's acoustics, it should be noted that the sound system may not fit the space. Speakers are designed to direct sound, and,, depending on whether a wall is located closer or more distant, its coverage may saturate the entire audience or miss some seats altogether.

If the new sanctuary has a different balcony height sound may bounce off its face and/or be hidden from the area below. Although one speaker system may have covered the entire area in the church, where the design originated, the new space may require under-balcony delayed reinforcement. If the source of the sound cannot be seen from the listener's seat, it will not be heard directly and will be experienced at a lower volume after it takes the "scenic" route to the ears of listener. Sound may also arrive in increments at multiple times creating echoes and confusing the message.

It might seem that a good way to clear things up would be to scale the established working design to the new room's dimensions. This idea sounds good but may not work. When NASA tests scale models in a wind tunnel, not only are the test object's dimensions smaller, so are the molecules representing air. This keeps the ratio of air size for the model in proportion to the air as it would be for a full-size plane or other device by substituting a gas with a smaller molecule size than that of our oxygen  nitrogen atmosphere. Testing an acoustical device requires attention to this degree of detail, as well.

Since the choir and preacher would sound very strange if the sanctuary were filled with helium for a true scale model, a new sanctuary should have its own design or existing design corrected for new dimensions and sound travel distances as if starting from scratch. Sight lines should be verified and power adjusted along with speaker coverage angles to be sure everyone hears properly. Changes in room volume may require acoustical traps where the new design does not allow sound to fully develop or dissipate.

Performance will also suffer if the distance between singers and players is too spread out. To borrow a phrase from the recording industry, the performance should not sound "phoned-in." A reporter live in a distant foreign country will have an understandable delay or lag in response to the show's moderator. The organist should not be placed in a similar situation with the pianist or director across the stage during a performance where timing is critical. The choir may photograph well if spread across the sound stage, but it won't help the basses keep in time with the sopranos.

Using monitors to help folks to keep in time is a solution accompanied by yet another problem: sound splashing back from the stage wall. This can be reduced by adding acoustical wall panels behind the performers. As mentioned earlier, sound may be enhanced by adding delayed reinforcement under the balcony and in other areas, allowing more uniform volume. Objectionable natural delays creating interference may be reduced or eliminated by well-placed sound absorption along sanctuary walls. If the new room is smaller than its predecessor, perceived acoustical size may be increased by adding sound diffusers that double as low frequency bass traps. Sound bouncing back from a balcony face may be reduced with thick panels and semi-cylindrical traps in combination with alterations to the speaker focus.

While it has been stressed that a design should not be copied without adjustment or modification, if spaces are not identical, neither should microphone placement or wall design be taken at face value. Often in movies or television, the sound is recorded separately in a different environment. A microphone may be seen on camera backwards, a hard wall shown in place of the studio's soft absorbing walls, and performers appearing in the middle of the band when in real life they would be acoustically separated. What you see is not always what you get, and your eyes may be seeing something completely different from what your ears are hearing. Seeing should not necessarily be "believing" for sound. Hearing, maybe.

In summary, a tested, proven design is a good thing and can save time and money in producing a known result without budget surprises. However, even a minor physical change can thwart a proven design and produce a major difference in acoustical performance.

Nick Colleran is past-president of SPARS (Society of Professional Audio Recording Services), past president of the VPSA (Virginia Productions Services Association), a former recording artist and recording engineer. He is a principal of Acoustics First Corporation, which designs, manufactures and distributes products to control sound and eliminate noise for commercial, residential and industrial uses, www.acousticsfirst.com.









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