Electrical filtering of the audio bandwidth is
necessary. This can be done either through passive filtering or active
A passive crossovers is the traditional way to set up a filter design for speakers. Here, inductors and capacitors possibly in combination with resistors are used directly on the speaker terminals. The filter components must be calculated to handle the power requirement.
Active versus passive crossovers.
Active crossovers indicate the way in which electronic filtering before the power amplifier is applied. Usually opamps perform this task in combination with capacitors and resistors. Some differences between active filters and passive filters can be mentioned. This is just a limited list of differences and, in my opinion active filtering is actually always superior to passive filtering with the disadvantage of a more complex electronic filter/ amplifier system and thus more expensive.
- Less inter modulation distortion (IMD) because each power amplifier is used in a restricted bandwidth.
- Less low frequency overload of amplifier especially for the higher frequencies (above 100Hz).
- Increased dynamic range. A combination of a 60W and 30W amplifier (active) will reach comparable results on power and distortion level as one 175W amplifier with passive filtering.
- Improved impulse behavior for all frequencies.
- Prevention of high frequency resonance's that might be caused by passive filters.
- Better and more accurate filter results because of
the constant load of the amplifier with one single speaker without
This is also because active filtering allows easy manipulation of important quantities like amplitude, phase and group velocity.
- Improved subjective sound quality with active crossovers.
- Easy adaptation of SPL of each speaker to the room acoustics with active crossovers.
- Better coupling of low frequency amplifier to the
woofer. Speaker wiring is very short.
Implementation of the active crossovers.
In the speaker design on this web, active filtering is the key issue in the total design. All simulations on filter matching between speakers as described below are based on the mathematics of filters given on this website. The results of these simulations are shown in the graph for the complete speaker system.
The full crossover uses natural (second order) filtering via closed box design, Butterworth (BW) and Linkwitz-Riley (LR) filters. The audio set is combined with speakers specificly designed to work with the electronic filters. It uses a separate subwoofer and two speakers for the left and right channel (satellites) which, by itself can cover the full audio range.
The realisation of the active filters with its physical parameters is done using an own created program which calculates the (summing) reponses of the crossover (see picture above). Simulations on the electronic implementation is done using PSPICE. The graphs are shown below for the bass section. Different filter sections are displayed.
The blue curve in the amplitude-frequency characteristic indicates the resulting gain at the output of the filter. The green and red curve are from the high and low pass sections. The other graph shows the group velocity also for the same filter section. It can be observed that, for creating the correct amplitude curves, the group velocity rapidly increases near 25Hz (the yellow curve is the filter output). Nevertheless, this is already close to the inaudible bass range and will not negatively affect the bass perception.
The bass speaker is connected to the following three filtering parts:
The bass-mid speaker:
The high speaker:
Measurements on the electrical crossovers are indicated below. It shows a perfect match to the targeted calculations and simulations.