What does a crossover do?

Give each driver a suitable job

A woofer and tweeter have different strengths. A crossover limits their operating ranges and often adjusts sensitivity or response irregularities. There is a broad overlap around the chosen crossover frequency. Within it, both drivers radiate, so level, phase, timing and spatial separation all matter. The goal is one coherent loudspeaker, not merely two operating drivers.

Passive and active arrangements

A passive network operates after the power amplifier. Its inductors, capacitors and resistors interact with the actual driver impedance and may dissipate power. An active analogue or DSP crossover divides the signal before separate power-amplifier channels. Active control makes adjustments easier, but still requires suitable drivers, correct gain structure and acoustic verification.

The electrical curve is only part of the result

A driver already has its own amplitude and phase response. The baffle and mounting geometry add further effects. A 24 dB/oct electrical filter therefore does not guarantee a 24 dB/oct acoustic slope. For development, measure each driver in the intended enclosure, preserve consistent reference conditions and use its real electrical and acoustic data.

Why two quieter branches can sum flat

For ideal aligned fourth-order Linkwitz–Riley acoustic responses, each branch is about 6 dB down at crossover. Their complex sound pressures can still add to flat magnitude. Do not add decibel values or ignore phase. Two equally strong contributions arriving in opposition can instead produce a deep cancellation. Raising one driver does not resolve the underlying alignment problem.

Listen beyond one point

Vertically separated drivers have angle-dependent path differences. A flat on-axis sum can coexist with pronounced vertical cancellations. Directivity should also match reasonably through the transition: a narrowing woofer handing over to a much wider tweeter changes the energy sent into the room. A coaxial arrangement changes the geometry but does not automatically eliminate all acoustic issues.

Choose a safe overlap region

The crossover frequency is not a universal number inferred from diameter alone. Check tweeter resonance, excursion and recommended operation, and check woofer breakup and directivity. A shallow filter may leave substantial out-of-band energy. Electrical filter order, acoustic slope and permissible operating level belong in the same decision.

Develop, measure and repeat

Start with suitable drivers and a test enclosure. Define an acoustic target, adjust filtering and levels, then measure individual branches, the combined response and several angles. For passive designs also inspect impedance. Save intermediate states and level-match listening tests. A successful crossover usually becomes unobtrusive precisely because considerable work went into it.