Loudspeaker System Crossover Network

Building a passive crossover for a speaker involves designing a network of passive electrical components (resistors, capacitors, and inductors) that split an audio signal into different frequency ranges and direct those ranges to the appropriate drivers (such as woofers, midrange speakers, and tweeters) in a multi-driver speaker system.. Here the simple passive schematic diagram of audio crossover:

Loudspeaker System Crossover Network Notes:

• Capacitor must be non-polar capacitor types with a voltage rating of 50 volt or more (preferably 100 volt).
• Capacitor may be paralled to achieve specified values.
• Inductors should be air core. Do not mount inductors in top of each other.
• Resistors should be 100 Watts or more.

Passive crossover is made entirely of passive components, arranged most commonly in a Cauer topology to achieve a Butterworth filter. Passive filters use resistors combined with reactive components such as capacitors and inductors. Very high performance passive crossovers are likely to be more expensive than active crossovers since individual components capable of good performance at the high currents and voltages at which speaker systems are driven are hard to make. Polypropylene, metalized polyester foil, paper and electrolytic capacitors are common.

Inductors may have air cores, powdered metal cores, ferrite cores, or laminated silicon steel cores, and most are wound with enamelled copper wire. Some passive networks include devices such as fuses, PTC devices, bulbs or circuit breakers to protect the loudspeaker drivers from accidental overpowering. Modern passive crossovers increasingly incorporate equalization networks (e.g., Zobel networks) that compensate for the changes in impedance with frequency inherent in virtually all loudspeakers. The issue is complex, as part of the change in impedance is due to acoustic loading changes across a driver’s passband.