Equalization is the process where different frequencies are boosted or cut in order to achieve the desired resulting sound. Sometimes there is a need to boost or cut certain frequencies in your bass sound, because of the room environment.
Other times, it may be necessary to boost or cut certain frequencies for the type of music or the song that you are playing. But all of your components collectively have some sort of equalizing effect on the sound of your bass.
This starts with the bass itself, the amplifier that you use, the speaker system, and even the room itself contributing to boosting and cutting certain frequencies.
Most Equalization is accomplished with a graphic or parametric equalizer unit. The graphic usually have center frequencies listed at the bottom of the sliders, with each slider being able to adjust that frequency with a boost or cut.
The center spot on the slider is the flat position for that band, where there is no boosting or cutting of the frequency band. Pushing the slider above 0db starts to boost that frequency band. Pulling the slider below 0db is a cut in the frequency band. This is also known as filtering.
Equalizers also come in active circuitry and passive circuits. Active circuit types have less noise than passive ones but also cost more.
The parametric types have a knob that selects a center frequency, and another knob that controls the boosting or cut off that frequency.
Some amplifiers and pre-amplifiers also have a contour control knob. This is often a filtering circuit that changes the EQ either at a fixed frequency and varying the width of the bandpass, or sweeping a filter of sorts through a range of frequencies.
Below is a graphic equalizer which is built into a bass pre-amp, in the middle section. The center frequency bands are labeled at the bottom starting with 30hz, 40hz, 60hz, 100hz, 180hz, 340hz, 660hz, 1.3Khz, 2.5Khz, 5Khz, 10Khz, 15Khz. The boosting and cutting are +/-15db.
In my opinion, the best low frequency to boost is 80hz. This gives the bass a very solid, punchy bass sound. It is easily discernable by the human ear, and it does not compete with the bass drum sound in most bands.
High-frequency boosting is best done in the 1.2Khz to 3Khz range. It all depends on what you need for the moment, and how bright your strings on the bass are. As the strings become older, you will likely need to boost some of the higher frequencies. Also, boosting at the 3-4Khz range is common for many fretless bass sounds.
Mid-range frequencies between 300hz and 800hz for the bass are usually muddy sounding. I typically do not boost these frequencies. Some bass players prefer to cut the sound in this range. However, John Entwistle, of The Who, often had the 300hz band boosted significantly from my observations.
If you like the boosting at 80hz, remember to try playing all of the notes on the bass and see how it affects them. Sometimes in the upper range on the G string, around the 12 frets (on octave up), you may notice that the sound has thinned out. If this is the case, try adding some more boost at 150hz or 200hz.