DLS SOUND HANDBOOK Manual page 8

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