What Is Bass Crossover?

A bass crossover splits the bass signal into the different speakers of your subwoofer.

Bass crossover is an electronic filter that splits the bass frequency of an audio signal into separate bands that can be handled by individual speaker drivers optimized for those bands. Bass crossovers provide a fuller, more dynamic range of bass to an audio system.

Audio Crossovers

Audio crossovers are electronic filters that split the audio signal into separate frequency bands that can be handled by individual loudspeaker drivers optimized for those bands. A bass crossover is designed specifically to deal with the lower end of the audio spectrum, splitting the low- from the mid- and high-range frequencies and then directing that signal to a subwoofer for broadcast.

Crossover in Theory

Optimal audio crossover is relative to the signal and the task. If the separate bands are to be mixed back together again, the optimal crossover must then split the incoming audio signal into non-overlapping separate bands that do not interact. The resulting output signal will then be identical to the incoming signal in frequency, response and relative levels.

Purpose

Individual loudspeaker drivers cannot cover the entire range of an audio music signal. According to Linkwitz Lab, "[i]t is practically impossible for a single radiator to cover the 20 Hz to 20 kHz audio frequency range at adequate sound pressure levels," meaning that a single speaker cannot vibrate at all the frequencies necessary to produce adequate sound quality over the full audio spectrum. Audio systems without crossover suffer from a lack of acceptable volume and distortion, especially if the signal includes low frequencies to high frequencies. You may have noticed that bass amps used by bass players may have one large speaker on the bottom and one or more smaller speakers mounted above that: this is to accommodate the built-in bass crossover that is splitting the bass signal into its higher and lower ranges and sending those signals to the appropriate speaker.

Active vs. Passive Crossover

There are, generally, two types of crossover systems: active and passive. In a passive system, the crossover unit receives the audio signal from the amplifier and then splits the signal between the appropriate speakers. In an active system, the signal first goes to the crossover unit, is split, and then directed to separate amplifiers powering different speakers.

Optimal Bass Crossover Setting

Alan Lofft at Axiom Home Theaters recommends setting the crossover of subwoofers at 80hz (though he does advocate experimenting with different settings to achieve a smoother sound with digital signals) (see reference 2). However, the optimal crossover setting will depend on many factors, including the size of the room, the signal and your sound system. Audioholics recommends "setting the crossover frequency for at least 10Hz above the lowest frequency your main speakers can reproduce cleanly" (see reference 3), but goes on to say that experimenting with various settings is ultimately the ideal approach to finding the right crossover settings for your system.

References

• Linkwitz Lab: Crossovers
• Alan Lofft, Axiom Home Theaters: Receiver and Subwoofer Crossover Setup
• Audioholics: Selecting the Right Crossover for Your System