Active Equalizers vs. Passive Equalizers

 In TSM Studio Blog
  • By definition, equalization is classified as the process of manipulating specified frequencies by either boosting or attenuating (reducing) their amplitude. To take equalization a step further, we can categorize their unique designs by having either Active or Passive construction.
  • Simply put, the primary difference between a passive and active EQ lays in the circuit build. Passive EQs do not require a power supply whereas active EQ circuits do. To better make sense of these two designs, a comprehensive understanding of their components will allow you to differentiate the two designs and decide when to utilize each tool for the necessary task at hand.
  • Passive EQs affect tone without the use of powered components such as op-amps, tubes, or transistors. After all, the passive EQ is named after the sole inclusion of passive electronic components including capacitors, resistors, and inductors. Because only passive components are used, a make-up amplifier is required in order to bring the effected signal back to its original level. Passive EQs essentially function by only being able to subtract energy, therefore the output signal will output lower post-processing. In short, a boost to any frequency is actually a cut to all others.
  • Tip: Prior to using a passive EQ, make sure that the input signal is strong enough to withstand the subtractive EQ that will take place. It is also useful to understand that the central nervous system is more excited as a result of EQ boosts as opposed to dips. Make sure that if you A/B your signal pre and post-passive EQ, you take this cognitive effect into account and don’t mistake the loss of gain for a loss of quality.
    • Now that we understand passive EQs, we’ll discuss how active EQs work differently than passive EQs. Active EQs are completely different constructs in the sense that they contain powered components which allow for frequencies to also be boosted rather than only attenuated. By design, active EQs are much more complex in construction because of the potential for dozens of tubes, transistors, op-amps, capacitors and resistors to be present. With the inclusion of powered components, active EQs are more likely to color the sound and add harmonics and various distortions which can be pleasant to the ear (according to taste). A pre-amplifying circuit generally follows each stage of equalization, restoring the signal level to unity gain (equal input and output level).

 

  • Active EQ Pros:
    • Can color the source signal/add various distortions and other colorations
    • Has the internal components necessary to restore a signal to unity gain
    • More flexible by circuit design

 

  • Active EQ Cons:
    • Can add unwanted color
    • Tend to add more ambient noise that can compound in conjunction with a noisy signal path (ie: feeding the signal from an active EQ into a diode bridge compressor)
    • Inclined to distort when overdriven

 

  • Passive EQ Pros:
    • Sound “cleaner” due to the absence of powered components
    • Less likely to affect transient response
    • Affect frequencies without (as much) added color

 

  • Passive EQ Cons:
    • Require make-up amplifiers to restore unity gain
    • Less flexibility due to lack of powered components
    • Typically, more expensive than active EQs

 

  • Active EQ Examples:
    • API 5500
    • GML 8200
    • D.W. Fearn VT-4 Tube LC EQ
    • Buzz Audio REQ-2.2A
    • Electrodyne 2511

 

  • Passive EQ Examples:
    • Pultec EQP1-A
    • Pultec MEQ-5
    • Manley’s Massive Passive
    • Abbery Road RS56
    • Passeq Mastering Equalizer