The filter design of the loudspeakers
1. Bass - Low Mid
f1= 160 Hz
2. Low Mid - High Mid
f1= 800 Hz
3. High Mid - High
f1= 4000 Hz
All filters consist of 2 second order Butterworth elements in cascade (Linkwitz-Riley). For compensation of the parasitic phase of the other filters the crossover frequencies of the low-mid to high-mid filters are modified to 850 Hz and 750 Hz. The gain of the two middle sections is increased by 7 % to get the overall amplitude response flat.
The difference
between the "normal" filter and the "cascade" filter is that in the latter
case the low-pass filter of the bass section is taken from the
output of the low-pass filter of the low-mid section and the
high-pass filter of the tweeter is taken from the output of the
high-pass filter of the high-mid section. In that case the slopes of
the bass and tweeter
filters is doubled out of band but with
extra phase errors as a result. Therefore this option was not
selected.
The calculated overall passband and the individual filters look like this :
Enlarged to show the overall characteristic in more detail :
The phase of the sum of the filters in both options :
It is completely reworked now to enable anybody to calculate any 4-way 4th order electronic crossover filters they like. All the following characteristics are graphically presented :
- Frequency response of
individual outputs
- Combined frequency response
-
Phase response of individual outputs
- Combined phase
response
- Group delay
You can calculate
resistors and capacitors based on corner frequencies and Q's or you
can calculate the circuit responses if you know the component
values.
The filters measured with SpeakerWorkshop :
The differences in peak levels take into account the different sensitivities of the drivers and the different gains of the power amplifiers per channel. The light blue curve is the summed output, which is flat as you can see. The slightly darker blue curve is the same frequency response, but now with the baffle step compensation switched in.
A picture of the printed circuit board :
A picture of the finished board :
A picture of the finished filter (one channel) :
A screen print of the filter PCB design (PCB design program Andreas Waldherr) :
If you have any questions regarding this project write me at luc.henderieckx@telenet.be