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DLS SOUND HANDBOOK - PASSIVE X-OVER FILTERS
PASSIVE 6 dB LOW-PASS
A 6 dB x-over filter has a 6 dB slope / octave. The
output from an amplifier is only a quarter after falling
with 6 dB. A 6dB filter is also called 1:st order filter.
A common use for a 6 dB low-pass filter is for a
subwoofer to stop frequencies over, as for example,
100 Hz.
A 6 dB low-pass filter consists of a coil. The x-over
frequency is decided by the inductance value
measured in the unit Henry (H) and parts of a Henry.
For speakers we normally use coils with the unit mH.
1 H = 1000 mH.
1:st order 6 dB low-pass filter:
1 2 3 4 5 6
+
1 2 3 4 5 6
1 2 3 4 5 6
-
CALCULATION FORMULA:
L (mH) = 160 x Z
Fc
Z = speaker impedance in Ω
Fc = x-over frequency in Hz
L= Coil inductance in mH
When connecting coils in series the values are
added.
Use this formula when connecting in parallel:
1
1 + 1 + 1
=
L
L
L
L
Inductance values for different x-over frequencies:
Speaker impedance
X-over fq.
2Ω
Hz
L
(mH)
65
5
80
4
100
3,2
130
2,5
200
1,6
360
0,9
500
0,65
800
0,4
1000
0,32
X-over frequencies at given values:
10 mH
6,3 mH
2Ω
32 Hz
50 Hz
4Ω
64 Hz
101 Hz
8Ω
128 Hz
203 Hz
L
4Ω
8Ω
L
L
(mH)
(mH)
10
20
8
16
6,4
12,8
5
10
3,2
6,4
1,75
3,5
1,3
2,6
0,8
1,6
0,64
1,28
1,75 mH
183 Hz
365 Hz
730 Hz
PASSIVE 6 dB HIGH-PASS
A 6 dB high-pass x-over filter consists of a capacitor.
The crossover frequency varies with the capacitor
value that is measured in the unit Farad and parts of
Farad. Normally we use μF values for speakers.,
1 F = 1000 000 μF
Capacitor values from approx. 10 μF and up are
normally of bipolar electrolytic type. For lower values
we often use polyester capacitors. A capacitor as in
the drawing below let the high frequencies pass and
stops the lower.
1:st order 6 dB high-pass filter:
+
-
CALCULATION FORMULA:
C (μF) = 160000
Fc x Z
Z = speaker impedance in Ω
Fc = x-over frequency in Hz
C = Capacitor value in μF
When connecting capacitors in parallel the values
are added. Use this formula when connecting in
series.
1
1 + 1 + 1
=
C
C
C
C
Capacitor values for different x-over frequencies:
Speaker impedance
X-over fq.
2Ω
Hz
C
(μF)
80
1000
100
800
130
600
200
400
500
160
800
100
1000
80
2000
40
5000
16
X-over frequencies at given values:
300 μF
200 μF
2Ω
266 Hz
400 Hz
4Ω
133 Hz
200 Hz
8Ω
67 Hz
100 Hz
7
C
4Ω
8Ω
C
C
(μF)
(μF)
500
250
400
200
300
150
200
100
80
40
50
25
40
20
20
10
8
4
150 μF
50 μF
6,8 μF
533 Hz
1,6 kHz 11,7 kHz
266 Hz
800 Hz 5,85 kHz
133 Hz
400 Hz 2,92 kHz
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