Crossover
Canonical Definition
A crossover is a set of filters and level, polarity, or timing decisions that assigns frequency regions to drivers or channels and creates a controlled acoustic handoff between them.
The electrical filter combines with the driver, enclosure, mounting, level, polarity, delay, acoustic center, and listening geometry. The measured acoustic handoff is what the cabin hears.
Three Basic Filter Jobs
| Filter | Passes | Common use |
|---|---|---|
| High-pass | Frequencies above the transition region | Protect tweeters, mids, midbass, and ported subwoofers from excessive low-frequency demand |
| Low-pass | Frequencies below the transition region | Limit upper output from subwoofers, midbass, and midrange channels |
| Band-pass | A region between high-pass and low-pass limits | Define the usable band for midbass or midrange drivers |
“Crossover Frequency” Can Mean Different Things
- Electrical corner: the frequency entered in the DSP or defined by the filter transfer function.
- Driver intersection: where two measured driver magnitudes cross.
- Acoustic target frequency: the intended center of complementary acoustic slopes.
- Summation region: the wider band where both drivers contribute enough energy to interact.
Record which meaning is being used. A statement such as “crossed at 3 kHz” is incomplete without the filter type, order, measured response, polarity, delay, and driver pair.
Choose The Region Before The Alignment
A defensible crossover region exists where both drivers can operate cleanly enough to overlap.
- Measure or obtain reliable data for each driver's installed response and distortion.
- Check excursion, thermal, and power limits at the intended level.
- Check directivity: the larger driver should not be excessively narrow before the smaller driver takes over.
- Check center-to-center spacing and mounting geometry.
- Choose a region with useful overlap, then choose the electrical filters that produce the desired acoustic slopes.
The safe crossover depends on the specific driver, slope, level, distortion, excursion, loading, equalization, and manufacturer guidance.
What LR4 Actually Guarantees
An ideal fourth-order Linkwitz-Riley low-pass and high-pass pair is -6 dB at the transition frequency and has matching phase there. That mathematical result assumes the two paths actually achieve the intended complementary transfer functions.
In a real vehicle, selecting “LR24” on both channels does not guarantee an acoustic LR4 crossover. The result can miss the target because of:
- driver natural rolloff or breakup
- different acoustic-center locations
- level mismatch
- delay and propagation differences
- mounting and boundary effects
- directivity and observation angle
LR4 is a useful starting family, not an automatic “flat sum” button.
Protection And Integration Are Separate Checks
| Question | Evidence |
|---|---|
| Is the driver protected? | Excursion, distortion, thermal behavior, filter attenuation, and operating level |
| Do adjacent drivers sum? | Individual magnitude and phase, normal sum, reverse-polarity comparison, and timing reference |
| Is coverage acceptable? | Nearby-position or angle measurements through the overlap region |
| Is headroom preserved? | DSP and amplifier levels after crossover EQ, shelves, and channel gain are applied |
Practical Workflow
- Define the driver pair, listening positions, and required output.
- Measure each driver individually with safe protection.
- Choose a crossover region from usable bandwidth and coverage.
- Apply initial filter types, frequencies, slopes, levels, polarity, and delay.
- Measure individual acoustic slopes with a common timing reference.
- Measure the normal sum and a reverse-polarity comparison when appropriate.
- Correct level, polarity, delay, filter shape, or geometry before broad EQ.
- Repeat at nearby positions or angles.
- Recheck protection, distortion, and gain structure at the intended level.