Signal Processors > Equalizers and Problem Solving Electronics
Equalizers and Problem Solving Electronics
The primary purpose of the Equalizer is the tune the speakers to the room. The sound that a listener hears in a church is comes from three different sources. They are, the sound coming directly from the source (voice or instrument), the sound coming directly from the speakers, and the sound being reflected by the room surfaces.
Any speaker system has non-linearities in its frequency response. In addition to this, every room has unique echo and resonance characteristics. To complicate things further, the placement of the speaker affects its frequency response due to variations in reflection from the wall, ceiling and floor surfaces.
The purpose of the equalizer is to tune the speaker system to the room. This cannot be done properly by ear. We need to use a spectrum analyzer and pink noise generator. By feeding pink noise (equal energy per octave) through the system we can measure the direct and reflected sound in the room using a calibrated microphone and spectrum analyzer. Using this method, we can tune not only the frequency response of the speakers, but also compensate for speaker position and room resonance. In this manner, assuming you have good speakers, we can provide accurate sound in the room. If you recall above, the third source is directly from the voice or instrument, so that is already accurate.
By tuning the system properly, we not only achieve accurate sound, but also reduce feedback. Feedback occurs primarily at the resonance frequencies of the room. By tuning out these resonances, we reduce the feedback problems.
The two main applications for a compressor / limiter in live sound are limiting speaker volume, and evening out speech variations from a microphone.
Assuming that your power amplifier rating is well matched to your speakers, and no one will be operating the system at excessive volume levels, you should have no need to limit the amplifier. In some cases however, this can happen. If it does, the amplifier may produce a high level distortion which can damage the speaker. Even if it doesn't affect the speaker, the excessive sound pressure level can cause short and possibly long term damage to ears.
A good solution to this, is to install a compressor / limiter between the mixer and amplifier. When it is adjusted properly, it will have no affect on the sound until the volume reaches a predetermined level. At this point the unit will prevent the level from increasing beyond that point. This way, the amplifier will not distort.
The other main application is evening out microphone or instrument levels. By connecting the compressor to the insert jack on the appropriate mixer channel you can compress the source volume as desired. If a person speaks quietly, or in a normal voice, the sound will not be affected. As they get louder, above a set threshold, the compressor will reduce the level to maintain a reasonably constant volume.
One of the main problems with church sound is getting enough volume before feedback. The first line of defense is to use good microphones and speakers which are properly suited to the room and applications. Next we need to properly tune the speakers to the room using a graphic equalizer. Once these steps have been taken, we can further reduce the problem using a feedback suppresser.
The AFS224 feedback suppresser automatically searches for and destroys feedback. It is a digital device with 24 notch filters. When feedback starts to occur, the unit determines the feedback frequency and inserts a notch filter to eliminate the feedback. If feedback reoccurs at a separate frequency, it assigns the second filter to eliminate the new feedback. In this manner it continues to eliminate if and when it occurs. The notches are very narrow and are virtually unnoticeable to the ear.
Not only does this unit eliminate feedback when it starts, it also increases the gain before feedback of the microphone or sound system. By notching out the feedback frequencies, you can increase the overall volume safely.
We use a Driverack 260 in almost all the sound systems we install is the Driverack260. It combines all of the above functions into a single, programmable unit.
The Drive Rack 260 is an excellent multifunction sound system processor. It combines a dual 28 band equalizer, dbx compressor, feedback eliminator, sub-harmonic synthesizer, six channel output with parametric EQs, limiters and alignment delays. The 260 also has a Real Time Analyzer and Pink Noise generator with Auto EQ. It can be programmed by computer (cable and software included) or through the front panel.
Using the Driverack 260, we can process an entire sound system with just this one device. For example, on a large system we can:
- Tune the main speakers to the room using the 28 band stereo
- Tune and delay a second set of speakers part way back using
delay and parametric equalizers
- Tune and delay a third and fourth set of speakers using more
delay and parametric equalizers
- Compress and limit the overall volume of the system to protect
speakers and ears
- Suppress feedback to increase the system gain before feedback and suppress annoying squeals
Even on a small sound system, the graphic equalizer and feedback suppresser are great to have. The compressors can be used to increase and even out your recording levels.