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Equalization

A carefully equalized sound system blends electroacoustic controls with the effects produced by the acoustics of the space. Careful design requires paying attention to detail, knowing when to ignore something and knowing when to stop making adjustments. It is definitely not something you can do in five minutes. However, with the help of a real-time analyzer, or measurement system; SMAART, TEF, or other analysis tool and (1 or 2) well trained ears, the ideal equalization curve can be actualized. The fundamentals of this process aren't necessarily complicated but they can sometimes be tedious.

  • Aiming. Take the time to ensure that the loudspeaker(s) will cover the listening area. Walk the area with a sound level meter. A good system should vary no more than +/-2dB front to back and +/-2dB side to side. Use your ears as well, listening for obvious changes in timbre as well as comb-filter effects. If there are any coverage problems, solve them before attempting any sort of system equalization.
  • Balance. Adjust the crossover's balance controls for the flattest response between the various system elements (low and hi, low, mid and hi, etc.).
  • Rough Tuning. Place the measurement microphone in a typical audience seating location. Make a measurement. Save it! Move the microphone to another location. Repeat the measurement and storage process. You'll want to measure several locations that represent a reasonable sample of listening area. In large systems, you'll need to do this by zones (assuming that each zone has its own equalizer). Now average the stored curves and plot the result. This average curve is the inverse of the curve that you'll need to create using the equalizer. You can make this less time consuming by using a microphone multiplexer and several microphones located in different locations. If you see a major dip or peak during any individual measurement, be sure to move the microphone to check for room nodes, or cancellation caused by a nearby reflecting surface.
  • Fine tuning. Its time to listen now. You may want to alter the rough tuning slightly in the interests of making the system sound more natural. You may need to change the basic high-frequency/low-frequency balance of the system, either via the crossover, or via the equalizer.
  • Apply reduction before boost. In an attempt to fill 'r; fill-in' hole in the frequency response. The hole may be caused by some acoustic phenomenon within the room. Equalization won't fix the room issues. If necessary, you will need to find the source of the absorption, or reflection and remedy it.
  • Feedback Tuning. With a live microphone(s), bring the sound system gently up to feedback. If you have a compressor in the system, temporarily set its ratio as high as possible and lower the compression threshold. This will keep the system from running away with itself in a feedback loop as you approach the feedback threshold.
  • If (2) or more frequencies are ringing at once, you're probably done with the equalization process. If multiple frequencies are ringing you have found the threshold in the dynamic range where multiple frequencies will be feeding back. You have already caught the system and room modes. If necessary, add small amount of attenuation to reduce the gain at the feedback frequency. Raise the gain again. You should stop when the system rings at (2) or more frequencies simultaneously. Again, Listen to the system and make adjustments needed for naturalness. A persistent gain-before-feedback problem may be the result of poor aiming of loudspeaker performance, or poor placement of microphones. Be sure to restore the compressor settings to their original state at the end of this gain pushing feedback discovery process.