Car Audio / Passive Crossovers, First Order Filters, 6dB per Octave

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First Order Filters:
• First Order Low Pass
• First Order High Pass
• First Order Band Pass
• First Order Narrow Band Pass

First Order Low Pass Filters

First order low pass filters consist of a coil in series with a loudspeaker. The larger the coil size (mHy), the lower the crossover frequency. For a 100 Hz first order low pass filter for a 4 ohm load, L1 = 6.36 mHy. For a 50 Hz low pass filter for a 4 ohm load, L1 = 12.73 mHy. For a 100 Hz first order low pass filter for a 2 ohm load, a 3.18 mHy coil is needed. To calculate values, use this calculator or the appropriate chart.

1st Order Low Pass Filter (6 dB per Octave)

1st Order Low Pass Filter (6 dB per Octave)

Using a 100 Hz first 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 75% or 6 dB. At 400 Hz, power is reduced by 93.75% or 12dB, and so on.

1st Order 100 Hz Low Pass Filter Curve

First Order High Pass Filters

First order high pass filters consist of a capacitor in series with a loudspeaker. The larger the capacitor size (µfd or mfd) is, the lower the crossover frequency. For a 5000 Hz first order high pass filter for a 4 ohm load, C1 = 7.96 µfd. For a 4000 Hz high pass filter for a 4 ohm load, C1 = 9.95 µfd. For a 5000 Hz first order high pass filter for a 6 ohm load, a 5.31 µfd capacitor is needed. To calculate values, use this calculator or the appropriate chart.

1st Order High Pass Filter (6 dB per Octave)

1st Order High Pass Filter (6 dB per Octave)

Using a 5000 Hz first 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 75% or 6 dB, and by 93.75 % at two octaves and so on.

1st Order 5000 Hz High Pass Filter Curve

1st Order 5000 Hz High Pass Filter Curve

First Order Band Pass Filters

First order band pass filters consist of a capacitor in series followed by a coil in series with a loudspeaker. Either the capacitor or coil may be first in line. This is a combination of a high pass filter and a low pass filter which allow the band of frequencies between the two crossover frequencies to pass. The high pass crossover frequency point must be lower than the low pass crossover frequency point.

1st Order Band Pass Filter (6 dB per Octave)

1st Order Band Pass Filter (6 dB per Octave)

As with the first order low pass and high pass filters, power above and below the respective crossover frequncies will be reduced by 75% or 6 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.

First Order Narrow Band Pass Filters

First order narrow band pass filters also consist of a capacitor in series followed by a coil in series with a loudspeaker. The capacitor and coil names are the same as a standard band pass filter, but use different values. Use this calculator or the appropriate chart.

6 dB Narrow Band Pass Capacitor and Coil Indentification

6 dB Narrow Band Pass Capacitor and Coil Indentification

<< Previous - Low Pass, Bandpass, Highpass Filters

Next - Second Order Filters >>

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Car Audio / Passive Crossovers, First Order Filters, 6dB per Octave

First Order Low Pass Filters

First Order High Pass Filters

First Order Band Pass Filters

First Order Narrow Band Pass Filters

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