3 way loudspeaker series network
PrefaceThe first design was implemtented in 1999 and since it has been one modification after another. Through the years, I have tried out many different filter configurations for this loudspeaker system:
Currently, I am a believer in the serial filtering scheme because it is component-inexpensive and therefore requires fewer lossy components (which can consequently be better). The possiblities are many: You can have in-phase coherence of the drivers, any filter order you like, impedance compensation networks can be included and the sound is often much more "forward", depending on the filter Q which is very freely chosen for each of the drivers.
In short: an inexpensive design that often sounds better than the sophisticated ones...
Modelling the EnclosureThis design is based on the enclosure that I used for my first 3-way loudspeaker system. However, a small modification has been made, since I moved the tweeter from the cement ball down inside the midrange enclosure. This means that the tweeter is not perfectly time-aligned with the midrange driver longer due to my current setup.
Schematic of the loudspeaker and how it is used in the setup.
This changed arrangement of the tweeter meant that I could alter the apperance of the loudspeaker slightly, which I think was a major improvement of the WAF. (Wife acceptance Factor) A picture of the left channel and my stereo system can be seen here
I modelled the responses (acoustical and electrical) of the loudspeaker drivers mounted in the enclosure using matlab. Using these and electrical circuit models made in matlab, I was able to simulate both the electrical and acoustical characteristics of the loudspeaker system
The bass driver.
Simulated acoustical response of PL22 mounted in a sealed enclosure of 50 liters.
Simulated electrical response of PL22 mounted in a sealed enclosure of 50 liters.
The midrange driver.
Simulated acoustical response of PL27.
Simulated electrical response of PL11.
Simulated acoustical response of Scanspeak 9500 tweeter.
Simulated electrical response of Scanspeak 9500 tweeter.
The filter networkIn the design of the loudspeaker system, I used the models for the transducers which are depicted above. I wanted a system which was had a relatively constant acoustical frequency magnitude transfer function, a reasonably high impedance and a The circuit depicted below is what I came up with (twe tweeter is actually connected with opposite polarity as the bass and midrange, which I forgot when I made the drawing).
Electrical circuit diagram used in the loudspeaker system.
The electrical characteristics of this filter including the modelled electrical characteristics of the drivers is depicted below.
The electrical characteristics (with the tweeter connected in phase).
The impedance seen by the amplifier is not at all frequency independent due to the tweeter/midrange, but it is never the less higher than 4 Ohm for all frequencies.
The impedance seen by the amplfier.
The acoustical output is relatively constant for all frequencies and the drivers work in phase for all frequencies.
The acoustical characteristics of the loudspeaker system.