Acoustic Crossover

Canonical Definition

An acoustic crossover is the measured magnitude, phase, and directional handoff between drivers after electrical filtering, driver response, enclosure or mounting, level, polarity, delay, acoustic center, and propagation have all combined.

Build the acoustic target, not matching software screens.

Two channels can both display LR24 at 3 kHz and still produce different slopes, phase, and coverage in the vehicle.

What Creates The Acoustic Result

Installed acoustic response =
  electrical filter
× driver transfer function
× enclosure / mounting / boundary response
× level and EQ
× polarity and delay
× acoustic-center geometry
× propagation and directivity

Because these factors multiply or add as complex quantities, a crossover cannot be judged from magnitude settings alone.

Complementary Acoustic Slopes

A well-integrated driver pair normally has:

enough clean bandwidth overlap to shape both paths
compatible magnitude through the overlap region
useful relative phase where both drivers contribute
safe excursion and distortion behavior
acceptable directivity and coverage through nearby positions

The target does not have to be a textbook Linkwitz-Riley shape, but it must be deliberate, measurable, and appropriate to the system goal.

Measurement Sequence

Fix microphone position and timing-reference method.
Measure Driver A alone with final mounting, polarity, delay, level, and initial filters.
Measure Driver B alone under the same conditions.
Overlay magnitude and phase through at least the useful overlap region.
Measure the normal-polarity sum.
Reverse one driver's polarity deliberately and measure the comparison.
Repeat at nearby positions or angles.
Adjust one variable at a time and document the result.

How To Read The Sum

Observation	Possible interpretation	Next check
Normal sum rises smoothly above each individual trace	Useful constructive summation	Check phase and nearby positions
Normal sum has a broad dip	Level, polarity, delay, filter, or acoustic-center mismatch	Compare individual phase and reverse-polarity result
Reverse-polarity trace creates a deep stable null	Drivers are closely aligned through that band	Return to intended polarity and check coverage
Reverse null is shallow or split	Slopes or phase do not track consistently	Adjust level, delay, filter shape, or all-pass correction
On-axis sum is good but nearby response collapses	Lobing or directivity mismatch	Review spacing, crossover region, and mounting angle

A reverse-polarity null is a diagnostic tool, not a universal scoring rule. Its useful depth and shape depend on the intended alignment, measurement geometry, smoothing, noise, and driver directivity.

Natural Rolloff Is Part Of The Design

Do not treat a driver's natural response as a problem that must always be flattened before crossover design. The natural slope can be combined with a gentler electrical filter, shaped with EQ, or used to form the target directly.

Conversely, breakup, resonances, or insufficient extension may make the chosen region unsuitable even when the software can create the requested filter.

Acoustic Center And Delay

Physical cone or dome location is only a starting geometry. The effective acoustic center may change with frequency, loading, horn geometry, and the chosen phase reference. Use delay to improve the measured relationship, but do not expect one delay value to erase every frequency-dependent difference.

When To Change The Design

Stop adjusting filters and reconsider the hardware or geometry when:

one driver is highly distorted or excursion-limited through the overlap
the larger driver is already too directional at the chosen frequency
center-to-center spacing produces unacceptable lobing
the required EQ or all-pass correction is extreme
the solution works only at one tiny microphone position