Equalization

Canonical Definition

Equalization is intentional frequency-dependent gain shaping used to move a system response toward a defined target within the limits of headroom, driver capability, spatial consistency, and the underlying acoustic cause.

EQ changes the response; it does not automatically fix the cause.

Routing, polarity, delay, crossover, directivity, placement, distortion, rattles, and deep interference nulls must be diagnosed before filter count becomes the strategy.

Classify The Problem First

Measured feature	Possible action	Required caution
Broad tonal tilt	Shelf filter or broad low-Q correction	Check target level, channel balance, and driver range first
Repeatable resonance peak	Measured peaking cut or notch	Match frequency and width; confirm decay and nearby positions
Stable broad deficiency within safe bandwidth	Limited boost may be justified	Account for headroom, power, excursion, and distortion
Deep narrow position-dependent dip	Usually fix geometry, phase, delay, crossover, or source contribution	Do not assume boost can fill an interference null
Natural driver rolloff	Respect it, reshape it, or change the crossover / driver	Do not force unsafe extension to match a line
Level mismatch	Channel gain or trim	EQ is not the correct substitute for overall level

Cuts And Boosts Are Tools, Not Moral Categories

“Always cut, never boost” is a useful beginner warning against wasting headroom, but it is not a complete engineering rule.

Cuts: can reduce peaks and preserve headroom, but many cuts may lower the average level and lead to later gain compensation.
Boosts: can correct a stable response deficiency, but increase voltage, power, excursion, thermal demand, and clipping risk in the affected band.
Shelves: are often better for broad tonal shaping than a stack of narrow filters.
Narrow filters: are appropriate for narrow repeatable features, not for chasing every comb-filter ripple.

There is no universal 6 dB maximum boost. The acceptable amount depends on the available margin and the cause, bandwidth, Q, driver, amplifier, listening level, and target.

Headroom Cost Of Boost

Boost	Voltage multiplier	Theoretical power multiplier at the same impedance
+3 dB	1.41×	2.0×
+6 dB	2.00×	4.0×
+10 dB	3.16×	10.0×

The system may clip, limit, compress, or run out of excursion before those theoretical demands are met. Recheck the full gain structure after meaningful positive filters or shelves.

Measurement Workflow

Correct routing, polarity, gain structure, crossovers, timing, and obvious hardware faults.
Define the target curve, match range, microphone positions, smoothing, and seating goal.
Measure individual drivers and crossover sums before full-system EQ.
Classify each feature: level, peak, broad trend, rolloff, cancellation, directivity, or noise.
Apply a small group of purposeful filters.
Predict the result, but then re-measure the real system.
Compare nearby positions before retaining narrow high-frequency correction.
Check headroom, distortion, excursion, and final listening balance.

Automatic EQ Is An Assistant

Automatic filter generation can match a measured trace toward a target, but the software does not automatically know:

which dips are spatial cancellation
the driver's excursion or thermal limit
whether the target level is correct
which seats matter
whether a narrow filter will remain useful after small movement
how much system headroom is acceptable

Limit the match range and boost, preserve manual filters when necessary, and verify predicted changes in both frequency and time domains.

What EQ Does Not Reliably Fix

broken, noisy, or clipped signal paths
polarity and routing mistakes
deep destructive interference at a single position
poor directivity or lobing across seats
driver distortion, excursion limits, or mechanical damage
rattles, buzzes, or panel resonance that requires physical treatment
missing bandwidth from an unsuitable driver or enclosure

Documentation Standard

For every retained filter, record:

Channel / driver:
Filter type:
Frequency:
Gain:
Q or bandwidth:
Measured cause:
Target or purpose:
Positions checked:
Headroom impact:
Verification trace: