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Bandwidth measured at half-power points (gain -3 dB, 2/2, or about 0.707 relative to peak) on a diagram showing magnitude transfer function versus frequency for a band-pass filter.
A medium-complexity example of a band-pass filter.

A band-pass filter (also bandpass filter, BPF) is a device that passes frequencies within a certain range and rejects (attenuates) frequencies outside that range.









Q factorEdit

A band-pass filter can be characterized by its Q factor. The Q-factor is the reciprocal of the fractional bandwidth. A high-Q filter will have a narrow passband and a low-Q filter will have a wide passband. These are respectively referred to as narrow-band and wide-band filters.





Loudspeaker enclosuresEdit

Compound or band-passEdit

Compound or 4th order band-pass enclosure

A 4th order electrical bandpass filter can be simulated by a vented box in which the contribution from the rear face of the driver cone is trapped in a sealed box, and the radiation from the front surface of the cone is into a ported chamber. This modifies the resonance of the driver. In its simplest form a compound enclosure has two chambers. The dividing wall between the chambers holds the driver; typically only one chamber is ported.

If the enclosure on each side of the woofer has a port in it then the enclosure yields a 6th order band-pass response. These are considerably harder to design and tend to be very sensitive to driver characteristics. As in other reflex enclosures, the ports may generally be replaced by passive radiators if desired.

An eighth order bandpass box is another variation which also has a narrow frequency range. They are often used to achieve sound pressure levels in which case a bass tone of a specific frequency would be used versus anything musical. They are complicated to build and must be done quite precisely in order to perform nearly as intended.[3]

Other fieldsEdit



See alsoEdit


  3. ^

External linksEdit

  Media related to Bandpass filters at Wikimedia Commons