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Car Audio / Passive Crossovers, Second Order Filters, 12dB per Octave

Second Order Filters:
Second Order Low Pass
Second Order High Pass
Second Order Band Pass
Second Order Narrow Band Pass

top of page Second Order Low Pass Filters
Second order low pass filters consist of a coil in series followed by a capacitor in parallel to a loudspeaker. The coil must come before the capacitor. For a 100 Hz second order low pass filter for a 4 ohm load, L2 = 9.00 mHy and C2 = 281 fd. For a 50 Hz low pass filter for a 4 ohm load, L2 = 18.00 mHy and C2 = 562 fd. For a 100 Hz second order low pass filter for a 2 ohm load, a 4.5 mHy coil and a 562 fd capacitor are needed. To calculate values, use this calculator or the appropriate chart.

2nd Order Low Pass Filter (12 dB per Octave)

Using a 100 Hz second order low pass filter on a woofer or woofers, at 200 Hz or one octave above the crossover frequency, power to the woofer(s) will be reduced by 93.75.% or 12 dB.

2nd Order 100 Hz Low Pass Filter Curve

top of page Second Order High Pass Filters
Second order high pass filters consist of a capacitor in series followed by a parallel coil to a loudspeaker. The capacitor must come before the coil. For a 5000 Hz second order high pass filter for a 4 ohm load, C2 = 5.62 fd and L2 = .18 mHy. For a 4000 Hz high pass filter for a 4 ohm load, C2 = 7.03 fd and L2 = .23 mHy. For a 5000 Hz second order high pass filter for a 6 ohm load, an 11.25 fd capacitor and a .09 mHy coil are needed. To calculate values, use this calculator or the appropriate chart.

2nd Order High Pass Filter (12 dB per Octave)

Using a 5000 Hz second order high pass filter on a tweeter or tweeters, at 2500 Hz or one octave below the crossover frequency, power to the tweeter(s) will be reduced by 93.75.% or 12 dB.

2nd Order 5000 Hz High Pass Filter Curve

top of page Second Order Band Pass Filters
Second order band pass filters consist of a 12 dB high pass filter followed by a 12 dB low pass filter. Either the high pass or low pass filter may be first in line. This combination of high pass and low pass filters allow a band of frequencies between the two crossover frequencies to pass with a steeper rate of cut-off than a first order filter. The high pass crossover frequency point must be lower than the low pass crossover frequency point.

2nd Order Band Pass Filter (12 dB per Octave)

As with the second order low pass and high pass filters, power above and below the respective crossover frequncies will be reduced by 93.75.% or 12 dB. Remember if the low pass frequency is less than 20 times the high pass frequency use this calculator for narrow band pass filters. For all others, use this calculator or the appropriate chart.

top of page Second Order Narrow Band Pass Filters
A 2nd Order Narrow band pass filter consist of a capacitor and coil in series followed by a parallel capacitor and coil to the loudspeaker. The capacitor and coil values and configuration are not the same as a standard band pass filter. Use this calculator or the appropriate chart.

12 dB Narrow Band Pass Capacitor and Coil Indentification
<< Previous - First Order Filters Next - Third Order Filters >>

Passive Crossovers:
Low Pass Filters
High Pass Filters
Band Pass Filters
Narrow Band Pass Filters
Zobel Filter
Acoustical Output & Power
First Order Filters
Second Order Filters
Third Order Filters
Formulas & Calculators
2 Ohm Reference Charts
4 Ohm Reference Charts
8 Ohm Reference Charts
Car Audio and Mobile Video:
Glossary of Terms
Passive Crossovers
Passive Crossover Calculators
Recommended Wire Sizes
Subwoofer Enclosures
Subwoofer Enclosure Calculators
Thiele - Small Parameters
Help and Additional Resources:
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