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DLS SOUND HANDBOOK - PASSIVE X-OVER FILTERS
CROSSOVERS
The ideal speaker, able to reproduce all frequencies
from lowest bass to highest treble, is not yet invented.
Instead we have to use two or more speakers where
each speaker is reproducing a part of the frequency
range.
To make this work the input signal to each speaker
driver must contain only the frequencies it´s desig-
ned for. For this purpose we need crossover filters.
ACTIVE CROSSOVERS
Crossovers can be ACTIVE or PASSIVE. An active
filter is connected before the amplifier line input. You
need one amplifier for each speaker pair which will
become rather expensive.
But the advantages are that it´s possible to mix
speakers with different impedance or sensitivity and
still be able to balance the system.
Most amplifiers are equipped with built-in active
crossovers that can be adjusted in frequency and also
switched in-out.
All DLS amplifiers have built-in active crossovers.
PASSIVE CROSSOVERS
Passive crossover consists of coils and capacitors,
and sometimes resistors for impedance adaption. A
passive filter is connected between the amplifier and
the speaker and is of LC-type, (coil and capacitor).
A coil stops the higher frequencies while the low pas-
ses through, a capacitor works in the opposite way.
By changing the component values, different cross-
over frequencies are obtained. The coils must be of
high quality with a large wire area to avoid losses
and distortion. Air coils without iron core are the best
but they can be rather big for high values. For high
values we often use coils with an iron core. The best
capacitors are of polyester type. For large
capacitance values bipolar electrolytic capacitors are
used.
Resistors are used in a filter for impedance adap-
tion. Read the part about conjugate compensation.
A passive filter steals more power than an active.
CROSSOVER FREQUENCIES:
In a two-way system with separate tweeter a cross-
over frequency from 3 - 8 kHz is normal.
In a three-way system it´s normal to split the sub at 200-
400 Hz and the tweeter at 3 - 8 kHz.
In a four-way system the x-over frequencies can be
as follows. To the subwoofer 80-130 Hz, mid-bass 400-
600 Hz and the tweeter 3 - 8 kHz.
This is a just a recommendation. Depending upon the
speaker data and where the different elements are
mounted in the car, other x-over frequencies could be
better.
CROSSOVER EXAMPLES:
(without conjugate compensation)
3-WAY SYSTEM:
12 dB filter slope
+
1 2 3
1 2 3
1 2 3
10 mH
1 2 3
300 μF
-
Sub-bass
0-80 Hz80 Hz - 5 kHz
4-WAY SYSTEM:
12 dB filter slope
+
300 μF
1 2 3
1 2 3
10 mH
1 2 3
1 2 3
1 2
1 2
1 2 1 2
-
Sub-bass
0-80 Hz80 - 520 Hz 520 - 5 kHz 5 kHz -
The systems above are shown without impedance
compensation. Read below about conjugate links.
PHASE SHIFT IN PASSIVE CROSSOVERS
All passive crossovers will phase shift the signal.
A 6 dB filter shifts 90 degrees and a 12 dB 180
degrees. Because of this you should always try to
phase reverse the tweeter in a system to see what
phase is creating the best sound. In a 3-way system
it´s normal to phase reverse the tweeter. All tweeters
used in a system must have the same polarity
(phase). Also subwoofers with a 12 dB crossover
should you try to phase reverse. If the subwoofer cone
is moving but you don´t achieve any good bass you
can try to phase reverse. If two subwoofers are
connected with different polarity (phase), the sound
from each speaker will kill the sound from the other,
resulting in a poor bass reproduction.
CONJUGATE COMPENSATION:
Conjugate compensation is a way to equal the spea-
ker load over the whole frequency range. A 4 ohm
speaker can have an impedance peak up to 25 times
the normal at the resonant frequency (Fs). To make
the calculated crossover filter to match, you can
connect a conjugate link in parallel with the speaker.
It´s normally made of a capacitor and a resistor. If
you cant calculate the exact component values for
the conjugate link you can use a 33 μF capacitor in
series with a 3,9 ohm resistor to most 4", 5,25" and
6,5" speakers.
6
300 μF
5,6 μF
1 2 1 2
1 2 1 2
0,18
1 2
10 mH
1 2
1 2
mH
Mid-range
Tweeter
5 kHz -
50 μF
5,6 μF
1 2 1 2
1 2
1,75 mH
1 2
1 2
1 2
1 2
1 2
1 2 1 2
1 2 1 2
Mid-bass
Mid-range
Tweeter
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