In the process of operating live sound systems we are always striving to improve the quality of our sound. But we can fall into the trap of creating unintended consequences when applying changes to our sound systems.
I have found that a healthy awareness of basic potential consequences goes a long way in keeping us from being caught off-guard and finding that our action has done more harm than good.
Following are a list of often-encountered scenarios I will use to illustrate this concept. They will vary from the most simplistic things that the less experienced attempt to do through some that are perhaps not so obvious to more experienced live sound folks.
| 1 |
Problem: The choir is not loud enough or the coverage of the choir is spotty.
Solution: Add another mic or two.
Consequence: Coverage may (or may not) appear to be improved BUT due to the proximity of these mic’s to one another there is pronounced phase cancellation (aka: comb filtering) that messes up the overall choir sound.
| 2 |
Problem: Drums are too loud and you cannot get the drummer to play softer.
Simple solution: Enclose drummer in Plexiglas shields.
Consequence: Drums are slightly less loud but now we have destructive reflections (from the Plexiglas) entering the drum microphones. This combines with the direct sound from the drums and now the drums have much less definition.
Better Solution: Buy or build a “real” gobo system consisting of absorptive and blocking/reflective panels. Angle the Plexiglas panels so that the reflections are the least destructive.
| 3 |
Problem: The choir feels they cannot hear what they need to hear. This may be the band, the lead vocalists and/or themselves.
Simple solution: Grab an unused loudspeaker (or 2) and place it out in front of the choir. Feed a monitor mix of drums, keyboards, lead vocals and their own microphones into this new “monitor”.
Consequence: The choir monitor introduces acoustic energy which is nonaligned to the acoustic sources (origins) and the result is smeared sound, which the choir members perceive as unclear or not loud enough. They then ask for more level. This, in turn, may result in louder sound for the choir BUT this acoustic energy is also entering the choir microphones and the result is a deterioration of the sound that is being fed into the main loudspeaker system.
Also, because the monitors are sitting on the floor they cover the front row of the choir very well, but these folks also block the sound from covering those who are standing farther back.
Better solution: First of all, choirs have performed for thousands of years without the need for choir monitors. The first culprit (after that of poor projection from choir members) is likely to be that you have no acoustic reinforcement of your choir. Choirs need to be in “shells” that provide constructive reflections and which allow them to hear one another and to better project forward.
If you really must have choir monitors, get a good quality monitor loudspeaker system and position it so that it feeds into the rear of the choir microphones and covers the choir well. Usually this means flying the monitors from above. Then feed them only pitch and timing cues, plus lead vocals -- never themselves.
| 4 |
Problem: You have poor gain-before-feed back from your vocal monitors, and/or your vocal mic’s pick up too much stage leakage.
Solution: You decide a tighter microphone pickup pattern will improve this, so you buy super- or hyper-cardioid mics.
Consequence: You have less leakage, but you also have more feedback because the stage monitor position (directly in front of each singer) is now firing directly into the rear lobe of that super- or hypercardioid mic. You then move the monitors off-axis and have less feedback, but the singers are now covered unevenly.
Better solution: Well… there isn’t one, other than to get more wedges (which may not be affordable and clutters up the platform more) that will hit each singer from both sides. If you replace the wedges with IEM’s [in-ear monitors] you can take advantage of the tighter microphone patterns, completely eliminate feedback and reduce stage sound clutter.
| 5 |
Problem: You have surface-mounted loudspeakers hanging on your sanctuary walls which are a real eyesore, plus you are aware that the diffracted energy (lower frequencies that curl around the loudspeaker enclosures and reflect off the wall) is not good for your sound.
Solution: You decide to build closets into the walls and recess the loudspeakers and then hide them behind grilles.
Consequence: You have eliminated the visual obtrusiveness of the loudspeakers, but there is now a big “suck out” of mid-frequency energy that is caused by the cavity surrounding each loudspeaker. This cannot be equalized away.
Better solution: Simple. Fill the cavities with compressed fiberglass or closed cell insulating foam. This eliminates the cavity and returns the sucked out energy. You will now have invisible loudspeakers that also sound better. By the way; make sure that you use fire-rated grill material and, if it is fabric, that it is also acoustically transparent.
These are but a few of the “unexpected consequences” I have run across in over 32 years of trying to achieve better live sound. The bottom line is to completely think through each solution you come up before you implement it. Then, once you have made the “improvement”, you must also carefully evaluate what you have achieved.
Tom Young is the prinicipal consultant at Electroacoustic Design Services located in Oxford, Connecticut. EDS specializes in architectural acoustics, acoustic noise reduction and electroacoustic design for performance and worship spaces. For more information, visit www.dbspl.com.
