Crossovers and multiway speakers
A crossover divides the audio spectrum between two or more drive units.
A typical two-way speaker sends low frequencies to a woofer and high frequencies to a tweeter. A three-way system adds a midrange.
Passive crossovers
A passive crossover is installed between the amplifier and drivers. It uses inductors, capacitors, and resistors.
Advantages:
- Only one amplifier
- No external power for the crossover
- Self-contained
Challenges:
- Components interact with changing driver impedance
- Large inductors and capacitors can be costly
- Component resistance affects damping and sensitivity
- Fine adjustment requires measurement
Active and DSP crossovers
An active crossover operates before the power amplifiers. Each driver or frequency band receives its own amplifier channel.
DSP can also provide:
- Precise filter slopes
- Time delay
- Equalization
- Limiters
- Driver protection
- Phase correction
Its flexibility does not remove the need for good acoustic measurements.
Crossover frequency
A suitable crossover frequency must fall within the safe operating ranges of both drivers.
Check:
- Tweeter resonance and excursion
- Woofer breakup
- Driver directivity
- Driver spacing relative to wavelength
- Maximum output
- Distortion
- Thermal limits
Linkwitz-Riley filters
Fourth-order Linkwitz-Riley acoustic filters are common because the two driver outputs are each 6 dB down at the crossover and sum flat when they are properly aligned and in phase.
A practical design process
- Mount the drivers in the intended enclosure.
- Measure each driver’s response and impedance.
- Choose a crossover region where both drivers behave well.
- Design the initial filters.
- Account for driver offset and polarity.
- Measure on-axis and off-axis summation.
- Adjust the network.
- Check impedance and maximum output.
- Verify the final system at several angles and levels.