Musician Tips: Equalization



Equalizers are just one of many tools used today in sound reinforcement. Unfortunately, they are possibly the most overused and abused tool that is in the audio chain. In this short section, the reader should grasp a simple, yet effective understating of what an equalizer is designed to do.

Equalization was, in theory, designed by brass players in the 1600s to “tone” down the shrill notes of the horn. This was accomplished by strategically placing tapestries or hanging them around the rooms to dampen various frequencies. Edison’s phonograph was the first electronic device with an “EQ” system, having a passive tone control on it.

The first EQ designed for pro sound was “cut” only EQ. When all sliders on the EQ were all the way to the top, then, in theory, the sound was flat. This type of EQ was used for feedback control in large halls.

Equalizers have changed dramatically since that time in the 50s, as there are several varying types of EQs, all with specific uses and functions.

First, there is the “Octave” EQ. This has a gain control for each octave of sound. Usually these are very inexpensive, and they are usually found on home and car audio systems. The problem with this type is that it controls too much sound, losing valuable tones for greater enhancement.

The “Half-Octave,” or 15 band EQ is good for general equalization of small systems in small areas. This type of EQ gives the user two sliders for each octave in the audio spectrum.

Third-Octave,” also known as 31 band, gives very good control overall in the sound spectrum, with three gain controls for each octave of sound. This type of EQ is most commonly used in large sound systems.

Sixth-octave,” or 60 band have 6 gain controls, or sliders, for every octave in the spectrum. This is an uncommon type of EQ, as they are very cost prohibitive, and in the hands of an unknowledgeable person, it could become confusing.

Parametric” EQs allow the user to select the specific frequency that needs to be controlled. The selected frequency then may be cut or boosted as much as +-15db. They are very effective for controlling large sound systems in a small environment, or when seeking a particular tone for recording.

Notch Filters” are also used to control specific sounds yet are usually for cut only applications. Some notch filters give the user the ability to “zero in” on a troublesome frequency and cut it by as much as – 40db.

All of these devices are merely tools to help the sound engineer. They are not to be used to compensate for systems that are too small or poorly designed systems. A properly used EQ is used to correct specific problems in the room that the system is in, usually caused by sound reflection off walls, ceilings, floors, and other objects causing particular frequencies to appear to sound louder than other tones. Equalizers may be used to enhance an individual instrument, yet for overall room EQ the system should only attempt to bring the audio curve to a “flat” position. Feedback or reflection control is the greatest need for an EQ, allowing the audience to hear essentially what is actually in the music.

Is a totally flat sound overall desired? Generally not, as our ears are not flat in response. Flat merely gives us a reference point to work with (kind of a ground level, or index point). Our voices aren’t flat; no instrument is flat, yet mixers, amps and speaker cabinets need to be as close to flat as possible for design reference.

Just what is “flat?” A sound system or device becomes flat when each and every frequency throughout the spectrum is equal in level (volume) to all of the others. Although the spectrum goes much further, 20 Hz to 20 Kz has become the reference bandwidth for flat. No speakers, amp, microphone, mixer or other processing device is totally flat. Understanding this, given a speaker cabinet with a response curve shown below:



To achieve a “flat” sound, your EQ must look like:



Each place that the slider is about ‘0’ is gain, or added volume. If not used properly, gain takes away headroom, which increases the possibility of distortion. Each place the slider goes below ‘0,’ gain has been decreased, taking out sound and perhaps allowing for more headroom.  


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